From 8a20fba8eb1ac01a0de9355eff84af69d4636d96 Mon Sep 17 00:00:00 2001
From: wxiaoguang <wxiaoguang@gmail.com>
Date: Mon, 18 Nov 2024 13:25:42 +0800
Subject: [PATCH] Refactor markup render system (#32533)

Remove unmaintainable sanitizer rules. No need to add special "class"
regexp rules anymore, use RenderInternal.SafeAttr instead, more details
(and examples) are in the tests
---
 modules/html/html.go                          |  25 ---
 modules/htmlutil/html.go                      |  48 +++++
 modules/htmlutil/html_test.go                 |  15 ++
 modules/markup/asciicast/asciicast.go         |  15 +-
 modules/markup/common/html.go                 |  16 --
 modules/markup/common/linkify.go              |  18 +-
 modules/markup/console/console.go             |   7 +-
 modules/markup/csv/csv.go                     |  11 +-
 modules/markup/external/external.go           |   9 +-
 modules/markup/html.go                        | 110 ++++------
 modules/markup/html_codepreview.go            |  13 +-
 modules/markup/html_email.go                  |   2 +-
 modules/markup/html_emoji.go                  |  16 +-
 modules/markup/html_issue.go                  |  14 +-
 modules/markup/html_link.go                   |   6 +-
 modules/markup/html_mention.go                |   4 +-
 modules/markup/internal/finalprocessor.go     |  30 +++
 modules/markup/internal/internal_test.go      |  61 ++++++
 modules/markup/internal/renderinternal.go     |  82 ++++++++
 modules/markup/markdown/ast.go                |  30 +--
 modules/markup/markdown/goldmark.go           |  27 ++-
 modules/markup/markdown/markdown.go           | 188 ++++++++----------
 modules/markup/markdown/markdown_test.go      |  14 ++
 .../markup/markdown/math/block_renderer.go    |  12 +-
 .../markup/markdown/math/inline_renderer.go   |  12 +-
 modules/markup/markdown/math/math.go          |  39 +---
 modules/markup/markdown/meta_test.go          |   6 +-
 .../markup/markdown/transform_blockquote.go   |   7 +-
 modules/markup/markdown/transform_codespan.go |   3 +-
 modules/markup/markdown/transform_list.go     |   2 +-
 modules/markup/render.go                      |  79 ++++----
 modules/markup/sanitizer_custom.go            |  10 +-
 modules/markup/sanitizer_default.go           |  65 +-----
 modules/markup/sanitizer_default_test.go      |   3 -
 modules/setting/markup.go                     |  21 +-
 modules/svg/svg.go                            |   2 +-
 modules/templates/helper.go                   |  21 +-
 modules/templates/helper_test.go              |   4 -
 modules/templates/util_avatar.go              |   2 +-
 modules/templates/util_render.go              |   5 +-
 modules/templates/util_render_test.go         |  18 +-
 routers/web/repo/wiki.go                      |   2 +-
 42 files changed, 567 insertions(+), 507 deletions(-)
 delete mode 100644 modules/html/html.go
 create mode 100644 modules/htmlutil/html.go
 create mode 100644 modules/htmlutil/html_test.go
 delete mode 100644 modules/markup/common/html.go
 create mode 100644 modules/markup/internal/finalprocessor.go
 create mode 100644 modules/markup/internal/internal_test.go
 create mode 100644 modules/markup/internal/renderinternal.go

diff --git a/modules/html/html.go b/modules/html/html.go
deleted file mode 100644
index b1ebd584c6..0000000000
--- a/modules/html/html.go
+++ /dev/null
@@ -1,25 +0,0 @@
-// Copyright 2022 The Gitea Authors. All rights reserved.
-// SPDX-License-Identifier: MIT
-
-package html
-
-// ParseSizeAndClass get size and class from string with default values
-// If present, "others" expects the new size first and then the classes to use
-func ParseSizeAndClass(defaultSize int, defaultClass string, others ...any) (int, string) {
-	size := defaultSize
-	if len(others) >= 1 {
-		if v, ok := others[0].(int); ok && v != 0 {
-			size = v
-		}
-	}
-	class := defaultClass
-	if len(others) >= 2 {
-		if v, ok := others[1].(string); ok && v != "" {
-			if class != "" {
-				class += " "
-			}
-			class += v
-		}
-	}
-	return size, class
-}
diff --git a/modules/htmlutil/html.go b/modules/htmlutil/html.go
new file mode 100644
index 0000000000..9b5f5a92d8
--- /dev/null
+++ b/modules/htmlutil/html.go
@@ -0,0 +1,48 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package htmlutil
+
+import (
+	"fmt"
+	"html/template"
+	"slices"
+)
+
+// ParseSizeAndClass get size and class from string with default values
+// If present, "others" expects the new size first and then the classes to use
+func ParseSizeAndClass(defaultSize int, defaultClass string, others ...any) (int, string) {
+	size := defaultSize
+	if len(others) >= 1 {
+		if v, ok := others[0].(int); ok && v != 0 {
+			size = v
+		}
+	}
+	class := defaultClass
+	if len(others) >= 2 {
+		if v, ok := others[1].(string); ok && v != "" {
+			if class != "" {
+				class += " "
+			}
+			class += v
+		}
+	}
+	return size, class
+}
+
+func HTMLFormat(s string, rawArgs ...any) template.HTML {
+	args := slices.Clone(rawArgs)
+	for i, v := range args {
+		switch v := v.(type) {
+		case nil, bool, int, int8, int16, int32, int64, uint, uint8, uint16, uint32, uint64, float32, float64, template.HTML:
+			// for most basic types (including template.HTML which is safe), just do nothing and use it
+		case string:
+			args[i] = template.HTMLEscapeString(v)
+		case fmt.Stringer:
+			args[i] = template.HTMLEscapeString(v.String())
+		default:
+			args[i] = template.HTMLEscapeString(fmt.Sprint(v))
+		}
+	}
+	return template.HTML(fmt.Sprintf(s, args...))
+}
diff --git a/modules/htmlutil/html_test.go b/modules/htmlutil/html_test.go
new file mode 100644
index 0000000000..5ff05d75b3
--- /dev/null
+++ b/modules/htmlutil/html_test.go
@@ -0,0 +1,15 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package htmlutil
+
+import (
+	"html/template"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestHTMLFormat(t *testing.T) {
+	assert.Equal(t, template.HTML("<a>&lt; < 1</a>"), HTMLFormat("<a>%s %s %d</a>", "<", template.HTML("<"), 1))
+}
diff --git a/modules/markup/asciicast/asciicast.go b/modules/markup/asciicast/asciicast.go
index 0678062340..e92b78a4bc 100644
--- a/modules/markup/asciicast/asciicast.go
+++ b/modules/markup/asciicast/asciicast.go
@@ -7,7 +7,6 @@ import (
 	"fmt"
 	"io"
 	"net/url"
-	"regexp"
 
 	"code.gitea.io/gitea/modules/markup"
 	"code.gitea.io/gitea/modules/setting"
@@ -38,10 +37,7 @@ const (
 
 // SanitizerRules implements markup.Renderer
 func (Renderer) SanitizerRules() []setting.MarkupSanitizerRule {
-	return []setting.MarkupSanitizerRule{
-		{Element: "div", AllowAttr: "class", Regexp: regexp.MustCompile(playerClassName)},
-		{Element: "div", AllowAttr: playerSrcAttr},
-	}
+	return []setting.MarkupSanitizerRule{{Element: "div", AllowAttr: playerSrcAttr}}
 }
 
 // Render implements markup.Renderer
@@ -53,12 +49,5 @@ func (Renderer) Render(ctx *markup.RenderContext, _ io.Reader, output io.Writer)
 		ctx.Metas["BranchNameSubURL"],
 		url.PathEscape(ctx.RelativePath),
 	)
-
-	_, err := io.WriteString(output, fmt.Sprintf(
-		`<div class="%s" %s="%s"></div>`,
-		playerClassName,
-		playerSrcAttr,
-		rawURL,
-	))
-	return err
+	return ctx.RenderInternal.FormatWithSafeAttrs(output, `<div class="%s" %s="%s"></div>`, playerClassName, playerSrcAttr, rawURL)
 }
diff --git a/modules/markup/common/html.go b/modules/markup/common/html.go
deleted file mode 100644
index 5658839c6f..0000000000
--- a/modules/markup/common/html.go
+++ /dev/null
@@ -1,16 +0,0 @@
-// Copyright 2019 The Gitea Authors. All rights reserved.
-// SPDX-License-Identifier: MIT
-
-package common
-
-import (
-	"mvdan.cc/xurls/v2"
-)
-
-// NOTE: All below regex matching do not perform any extra validation.
-// Thus a link is produced even if the linked entity does not exist.
-// While fast, this is also incorrect and lead to false positives.
-// TODO: fix invalid linking issue
-
-// LinkRegex is a regexp matching a valid link
-var LinkRegex, _ = xurls.StrictMatchingScheme("https?://")
diff --git a/modules/markup/common/linkify.go b/modules/markup/common/linkify.go
index f84680205e..be6ab22b55 100644
--- a/modules/markup/common/linkify.go
+++ b/modules/markup/common/linkify.go
@@ -9,15 +9,27 @@ package common
 import (
 	"bytes"
 	"regexp"
+	"sync"
 
 	"github.com/yuin/goldmark"
 	"github.com/yuin/goldmark/ast"
 	"github.com/yuin/goldmark/parser"
 	"github.com/yuin/goldmark/text"
 	"github.com/yuin/goldmark/util"
+	"mvdan.cc/xurls/v2"
 )
 
-var wwwURLRegxp = regexp.MustCompile(`^www\.[-a-zA-Z0-9@:%._\+~#=]{2,256}\.[a-z]{2,6}((?:/|[#?])[-a-zA-Z0-9@:%_\+.~#!?&//=\(\);,'">\^{}\[\]` + "`" + `]*)?`)
+type GlobalVarsType struct {
+	wwwURLRegxp *regexp.Regexp
+	LinkRegex   *regexp.Regexp // fast matching a URL link, no any extra validation.
+}
+
+var GlobalVars = sync.OnceValue[*GlobalVarsType](func() *GlobalVarsType {
+	v := &GlobalVarsType{}
+	v.wwwURLRegxp = regexp.MustCompile(`^www\.[-a-zA-Z0-9@:%._\+~#=]{2,256}\.[a-z]{2,6}((?:/|[#?])[-a-zA-Z0-9@:%_\+.~#!?&//=\(\);,'">\^{}\[\]` + "`" + `]*)?`)
+	v.LinkRegex, _ = xurls.StrictMatchingScheme("https?://")
+	return v
+})
 
 type linkifyParser struct{}
 
@@ -60,10 +72,10 @@ func (s *linkifyParser) Parse(parent ast.Node, block text.Reader, pc parser.Cont
 	var protocol []byte
 	typ := ast.AutoLinkURL
 	if bytes.HasPrefix(line, protoHTTP) || bytes.HasPrefix(line, protoHTTPS) || bytes.HasPrefix(line, protoFTP) {
-		m = LinkRegex.FindSubmatchIndex(line)
+		m = GlobalVars().LinkRegex.FindSubmatchIndex(line)
 	}
 	if m == nil && bytes.HasPrefix(line, domainWWW) {
-		m = wwwURLRegxp.FindSubmatchIndex(line)
+		m = GlobalVars().wwwURLRegxp.FindSubmatchIndex(line)
 		protocol = []byte("http")
 	}
 	if m != nil {
diff --git a/modules/markup/console/console.go b/modules/markup/console/console.go
index d991527b80..06f3acfa68 100644
--- a/modules/markup/console/console.go
+++ b/modules/markup/console/console.go
@@ -6,8 +6,7 @@ package console
 import (
 	"bytes"
 	"io"
-	"path/filepath"
-	"regexp"
+	"path"
 
 	"code.gitea.io/gitea/modules/markup"
 	"code.gitea.io/gitea/modules/setting"
@@ -36,7 +35,7 @@ func (Renderer) Extensions() []string {
 // SanitizerRules implements markup.Renderer
 func (Renderer) SanitizerRules() []setting.MarkupSanitizerRule {
 	return []setting.MarkupSanitizerRule{
-		{Element: "span", AllowAttr: "class", Regexp: regexp.MustCompile(`^term-((fg[ix]?|bg)\d+|container)$`)},
+		{Element: "span", AllowAttr: "class", Regexp: `^term-((fg[ix]?|bg)\d+|container)$`},
 	}
 }
 
@@ -46,7 +45,7 @@ func (Renderer) CanRender(filename string, input io.Reader) bool {
 	if err != nil {
 		return false
 	}
-	if enry.GetLanguage(filepath.Base(filename), buf) != enry.OtherLanguage {
+	if enry.GetLanguage(path.Base(filename), buf) != enry.OtherLanguage {
 		return false
 	}
 	return bytes.ContainsRune(buf, '\x1b')
diff --git a/modules/markup/csv/csv.go b/modules/markup/csv/csv.go
index 3d952b0de4..a3e6bbaac6 100644
--- a/modules/markup/csv/csv.go
+++ b/modules/markup/csv/csv.go
@@ -7,7 +7,6 @@ import (
 	"bufio"
 	"html"
 	"io"
-	"regexp"
 	"strconv"
 
 	"code.gitea.io/gitea/modules/csv"
@@ -37,9 +36,9 @@ func (Renderer) Extensions() []string {
 // SanitizerRules implements markup.Renderer
 func (Renderer) SanitizerRules() []setting.MarkupSanitizerRule {
 	return []setting.MarkupSanitizerRule{
-		{Element: "table", AllowAttr: "class", Regexp: regexp.MustCompile(`data-table`)},
-		{Element: "th", AllowAttr: "class", Regexp: regexp.MustCompile(`line-num`)},
-		{Element: "td", AllowAttr: "class", Regexp: regexp.MustCompile(`line-num`)},
+		{Element: "table", AllowAttr: "class", Regexp: `^data-table$`},
+		{Element: "th", AllowAttr: "class", Regexp: `^line-num$`},
+		{Element: "td", AllowAttr: "class", Regexp: `^line-num$`},
 	}
 }
 
@@ -51,13 +50,13 @@ func writeField(w io.Writer, element, class, field string) error {
 		return err
 	}
 	if len(class) > 0 {
-		if _, err := io.WriteString(w, " class=\""); err != nil {
+		if _, err := io.WriteString(w, ` class="`); err != nil {
 			return err
 		}
 		if _, err := io.WriteString(w, class); err != nil {
 			return err
 		}
-		if _, err := io.WriteString(w, "\""); err != nil {
+		if _, err := io.WriteString(w, `"`); err != nil {
 			return err
 		}
 	}
diff --git a/modules/markup/external/external.go b/modules/markup/external/external.go
index 122517ed11..d28dc9fa5d 100644
--- a/modules/markup/external/external.go
+++ b/modules/markup/external/external.go
@@ -102,7 +102,7 @@ func (p *Renderer) Render(ctx *markup.RenderContext, input io.Reader, output io.
 
 		_, err = io.Copy(f, input)
 		if err != nil {
-			f.Close()
+			_ = f.Close()
 			return fmt.Errorf("%s write data to temp file when rendering %s failed: %w", p.Name(), p.Command, err)
 		}
 
@@ -113,10 +113,9 @@ func (p *Renderer) Render(ctx *markup.RenderContext, input io.Reader, output io.
 		args = append(args, f.Name())
 	}
 
-	if ctx == nil || ctx.Ctx == nil {
-		if ctx == nil {
-			log.Warn("RenderContext not provided defaulting to empty ctx")
-			ctx = &markup.RenderContext{}
+	if ctx.Ctx == nil {
+		if !setting.IsProd || setting.IsInTesting {
+			panic("RenderContext did not provide context")
 		}
 		log.Warn("RenderContext did not provide context, defaulting to Shutdown context")
 		ctx.Ctx = graceful.GetManager().ShutdownContext()
diff --git a/modules/markup/html.go b/modules/markup/html.go
index 16ccd4b406..e8799c401c 100644
--- a/modules/markup/html.go
+++ b/modules/markup/html.go
@@ -25,9 +25,6 @@ const (
 	IssueNameStyleRegexp       = "regexp"
 )
 
-// CSS class for action keywords (e.g. "closes: #1")
-const keywordClass = "issue-keyword"
-
 type globalVarsType struct {
 	hashCurrentPattern      *regexp.Regexp
 	shortLinkPattern        *regexp.Regexp
@@ -39,6 +36,7 @@ type globalVarsType struct {
 	emojiShortCodeRegex     *regexp.Regexp
 	issueFullPattern        *regexp.Regexp
 	filesChangedFullPattern *regexp.Regexp
+	codePreviewPattern      *regexp.Regexp
 
 	tagCleaner *regexp.Regexp
 	nulCleaner *strings.Replacer
@@ -88,6 +86,9 @@ var globalVars = sync.OnceValue[*globalVarsType](func() *globalVarsType {
 	// example: https://domain/org/repo/pulls/27/files#hash
 	v.filesChangedFullPattern = regexp.MustCompile(`https?://(?:\S+/)[\w_.-]+/[\w_.-]+/pulls/((?:\w{1,10}-)?[1-9][0-9]*)/files([\?|#](\S+)?)?\b`)
 
+	// codePreviewPattern matches "http://domain/.../{owner}/{repo}/src/commit/{commit}/{filepath}#L10-L20"
+	v.codePreviewPattern = regexp.MustCompile(`https?://\S+/([^\s/]+)/([^\s/]+)/src/commit/([0-9a-f]{7,64})(/\S+)#(L\d+(-L\d+)?)`)
+
 	v.tagCleaner = regexp.MustCompile(`<((?:/?\w+/\w+)|(?:/[\w ]+/)|(/?[hH][tT][mM][lL]\b)|(/?[hH][eE][aA][dD]\b))`)
 	v.nulCleaner = strings.NewReplacer("\000", "")
 	return v
@@ -129,7 +130,7 @@ func CustomLinkURLSchemes(schemes []string) {
 		}
 		withAuth = append(withAuth, s)
 	}
-	common.LinkRegex, _ = xurls.StrictMatchingScheme(strings.Join(withAuth, "|"))
+	common.GlobalVars().LinkRegex, _ = xurls.StrictMatchingScheme(strings.Join(withAuth, "|"))
 }
 
 type postProcessError struct {
@@ -164,11 +165,7 @@ var defaultProcessors = []processor{
 // emails with HTML links, parsing shortlinks in the format of [[Link]], like
 // MediaWiki, linking issues in the format #ID, and mentions in the format
 // @user, and others.
-func PostProcess(
-	ctx *RenderContext,
-	input io.Reader,
-	output io.Writer,
-) error {
+func PostProcess(ctx *RenderContext, input io.Reader, output io.Writer) error {
 	return postProcess(ctx, defaultProcessors, input, output)
 }
 
@@ -189,10 +186,7 @@ var commitMessageProcessors = []processor{
 // RenderCommitMessage will use the same logic as PostProcess, but will disable
 // the shortLinkProcessor and will add a defaultLinkProcessor if defaultLink is
 // set, which changes every text node into a link to the passed default link.
-func RenderCommitMessage(
-	ctx *RenderContext,
-	content string,
-) (string, error) {
+func RenderCommitMessage(ctx *RenderContext, content string) (string, error) {
 	procs := commitMessageProcessors
 	return renderProcessString(ctx, procs, content)
 }
@@ -219,10 +213,7 @@ var emojiProcessors = []processor{
 // RenderCommitMessage, but will disable the shortLinkProcessor and
 // emailAddressProcessor, will add a defaultLinkProcessor if defaultLink is set,
 // which changes every text node into a link to the passed default link.
-func RenderCommitMessageSubject(
-	ctx *RenderContext,
-	defaultLink, content string,
-) (string, error) {
+func RenderCommitMessageSubject(ctx *RenderContext, defaultLink, content string) (string, error) {
 	procs := slices.Clone(commitMessageSubjectProcessors)
 	procs = append(procs, func(ctx *RenderContext, node *html.Node) {
 		ch := &html.Node{Parent: node, Type: html.TextNode, Data: node.Data}
@@ -236,10 +227,7 @@ func RenderCommitMessageSubject(
 }
 
 // RenderIssueTitle to process title on individual issue/pull page
-func RenderIssueTitle(
-	ctx *RenderContext,
-	title string,
-) (string, error) {
+func RenderIssueTitle(ctx *RenderContext, title string) (string, error) {
 	// do not render other issue/commit links in an issue's title - which in most cases is already a link.
 	return renderProcessString(ctx, []processor{
 		emojiShortCodeProcessor,
@@ -257,10 +245,7 @@ func renderProcessString(ctx *RenderContext, procs []processor, content string)
 
 // RenderDescriptionHTML will use similar logic as PostProcess, but will
 // use a single special linkProcessor.
-func RenderDescriptionHTML(
-	ctx *RenderContext,
-	content string,
-) (string, error) {
+func RenderDescriptionHTML(ctx *RenderContext, content string) (string, error) {
 	return renderProcessString(ctx, []processor{
 		descriptionLinkProcessor,
 		emojiShortCodeProcessor,
@@ -270,10 +255,7 @@ func RenderDescriptionHTML(
 
 // RenderEmoji for when we want to just process emoji and shortcodes
 // in various places it isn't already run through the normal markdown processor
-func RenderEmoji(
-	ctx *RenderContext,
-	content string,
-) (string, error) {
+func RenderEmoji(ctx *RenderContext, content string) (string, error) {
 	return renderProcessString(ctx, emojiProcessors, content)
 }
 
@@ -333,6 +315,17 @@ func postProcess(ctx *RenderContext, procs []processor, input io.Reader, output
 	return nil
 }
 
+func isEmojiNode(node *html.Node) bool {
+	if node.Type == html.ElementNode && node.Data == atom.Span.String() {
+		for _, attr := range node.Attr {
+			if (attr.Key == "class" || attr.Key == "data-attr-class") && strings.Contains(attr.Val, "emoji") {
+				return true
+			}
+		}
+	}
+	return false
+}
+
 func visitNode(ctx *RenderContext, procs []processor, node *html.Node) *html.Node {
 	// Add user-content- to IDs and "#" links if they don't already have them
 	for idx, attr := range node.Attr {
@@ -346,47 +339,27 @@ func visitNode(ctx *RenderContext, procs []processor, node *html.Node) *html.Nod
 		if attr.Key == "href" && strings.HasPrefix(attr.Val, "#") && notHasPrefix {
 			node.Attr[idx].Val = "#user-content-" + val
 		}
-
-		if attr.Key == "class" && attr.Val == "emoji" {
-			procs = nil
-		}
 	}
 
 	switch node.Type {
 	case html.TextNode:
-		processTextNodes(ctx, procs, node)
+		for _, proc := range procs {
+			proc(ctx, node) // it might add siblings
+		}
+
 	case html.ElementNode:
-		if node.Data == "code" || node.Data == "pre" {
-			// ignore code and pre nodes
+		if isEmojiNode(node) {
+			// TextNode emoji will be converted to `<span class="emoji">`, then the next iteration will visit the "span"
+			// if we don't stop it, it will go into the TextNode again and create an infinite recursion
 			return node.NextSibling
+		} else if node.Data == "code" || node.Data == "pre" {
+			return node.NextSibling // ignore code and pre nodes
 		} else if node.Data == "img" {
 			return visitNodeImg(ctx, node)
 		} else if node.Data == "video" {
 			return visitNodeVideo(ctx, node)
 		} else if node.Data == "a" {
-			// Restrict text in links to emojis
-			procs = emojiProcessors
-		} else if node.Data == "i" {
-			for _, attr := range node.Attr {
-				if attr.Key != "class" {
-					continue
-				}
-				classes := strings.Split(attr.Val, " ")
-				for i, class := range classes {
-					if class == "icon" {
-						classes[0], classes[i] = classes[i], classes[0]
-						attr.Val = strings.Join(classes, " ")
-
-						// Remove all children of icons
-						child := node.FirstChild
-						for child != nil {
-							node.RemoveChild(child)
-							child = node.FirstChild
-						}
-						break
-					}
-				}
-			}
+			procs = emojiProcessors // Restrict text in links to emojis
 		}
 		for n := node.FirstChild; n != nil; {
 			n = visitNode(ctx, procs, n)
@@ -396,22 +369,17 @@ func visitNode(ctx *RenderContext, procs []processor, node *html.Node) *html.Nod
 	return node.NextSibling
 }
 
-// processTextNodes runs the passed node through various processors, in order to handle
-// all kinds of special links handled by the post-processing.
-func processTextNodes(ctx *RenderContext, procs []processor, node *html.Node) {
-	for _, p := range procs {
-		p(ctx, node)
-	}
-}
-
 // createKeyword() renders a highlighted version of an action keyword
-func createKeyword(content string) *html.Node {
+func createKeyword(ctx *RenderContext, content string) *html.Node {
+	// CSS class for action keywords (e.g. "closes: #1")
+	const keywordClass = "issue-keyword"
+
 	span := &html.Node{
 		Type: html.ElementNode,
 		Data: atom.Span.String(),
 		Attr: []html.Attribute{},
 	}
-	span.Attr = append(span.Attr, html.Attribute{Key: "class", Val: keywordClass})
+	span.Attr = append(span.Attr, ctx.RenderInternal.NodeSafeAttr("class", keywordClass))
 
 	text := &html.Node{
 		Type: html.TextNode,
@@ -422,7 +390,7 @@ func createKeyword(content string) *html.Node {
 	return span
 }
 
-func createLink(href, content, class string) *html.Node {
+func createLink(ctx *RenderContext, href, content, class string) *html.Node {
 	a := &html.Node{
 		Type: html.ElementNode,
 		Data: atom.A.String(),
@@ -432,7 +400,7 @@ func createLink(href, content, class string) *html.Node {
 		a.Attr = append(a.Attr, html.Attribute{Key: "data-markdown-generated-content"})
 	}
 	if class != "" {
-		a.Attr = append(a.Attr, html.Attribute{Key: "class", Val: class})
+		a.Attr = append(a.Attr, ctx.RenderInternal.NodeSafeAttr("class", class))
 	}
 
 	text := &html.Node{
diff --git a/modules/markup/html_codepreview.go b/modules/markup/html_codepreview.go
index 5ab9290b3e..5c88481d76 100644
--- a/modules/markup/html_codepreview.go
+++ b/modules/markup/html_codepreview.go
@@ -6,7 +6,6 @@ package markup
 import (
 	"html/template"
 	"net/url"
-	"regexp"
 	"strconv"
 	"strings"
 
@@ -16,9 +15,6 @@ import (
 	"golang.org/x/net/html"
 )
 
-// codePreviewPattern matches "http://domain/.../{owner}/{repo}/src/commit/{commit}/{filepath}#L10-L20"
-var codePreviewPattern = regexp.MustCompile(`https?://\S+/([^\s/]+)/([^\s/]+)/src/commit/([0-9a-f]{7,64})(/\S+)#(L\d+(-L\d+)?)`)
-
 type RenderCodePreviewOptions struct {
 	FullURL   string
 	OwnerName string
@@ -30,7 +26,7 @@ type RenderCodePreviewOptions struct {
 }
 
 func renderCodeBlock(ctx *RenderContext, node *html.Node) (urlPosStart, urlPosStop int, htm template.HTML, err error) {
-	m := codePreviewPattern.FindStringSubmatchIndex(node.Data)
+	m := globalVars().codePreviewPattern.FindStringSubmatchIndex(node.Data)
 	if m == nil {
 		return 0, 0, "", nil
 	}
@@ -66,8 +62,8 @@ func codePreviewPatternProcessor(ctx *RenderContext, node *html.Node) {
 			node = node.NextSibling
 			continue
 		}
-		urlPosStart, urlPosEnd, h, err := renderCodeBlock(ctx, node)
-		if err != nil || h == "" {
+		urlPosStart, urlPosEnd, renderedCodeBlock, err := renderCodeBlock(ctx, node)
+		if err != nil || renderedCodeBlock == "" {
 			if err != nil {
 				log.Error("Unable to render code preview: %v", err)
 			}
@@ -84,7 +80,8 @@ func codePreviewPatternProcessor(ctx *RenderContext, node *html.Node) {
 		//    then it is resolved as: "<p>{TextBefore}</p><div NewNode/><p>{TextAfter}</p>",
 		//    so unless it could correctly replace the parent "p/li" node, it is very difficult to eliminate the "TextBefore" empty node.
 		node.Data = textBefore
-		node.Parent.InsertBefore(&html.Node{Type: html.RawNode, Data: string(h)}, next)
+		renderedCodeNode := &html.Node{Type: html.RawNode, Data: string(ctx.RenderInternal.ProtectSafeAttrs(renderedCodeBlock))}
+		node.Parent.InsertBefore(renderedCodeNode, next)
 		if textAfter != "" {
 			node.Parent.InsertBefore(&html.Node{Type: html.TextNode, Data: textAfter}, next)
 		}
diff --git a/modules/markup/html_email.go b/modules/markup/html_email.go
index 32d0285eb4..cbfae8b829 100644
--- a/modules/markup/html_email.go
+++ b/modules/markup/html_email.go
@@ -15,7 +15,7 @@ func emailAddressProcessor(ctx *RenderContext, node *html.Node) {
 		}
 
 		mail := node.Data[m[2]:m[3]]
-		replaceContent(node, m[2], m[3], createLink("mailto:"+mail, mail, "mailto"))
+		replaceContent(node, m[2], m[3], createLink(ctx, "mailto:"+mail, mail, "" /*mailto*/))
 		node = node.NextSibling.NextSibling
 	}
 }
diff --git a/modules/markup/html_emoji.go b/modules/markup/html_emoji.go
index 6eacb2067f..c638065425 100644
--- a/modules/markup/html_emoji.go
+++ b/modules/markup/html_emoji.go
@@ -13,15 +13,13 @@ import (
 	"golang.org/x/net/html/atom"
 )
 
-func createEmoji(content, class, name string) *html.Node {
+func createEmoji(ctx *RenderContext, content, name string) *html.Node {
 	span := &html.Node{
 		Type: html.ElementNode,
 		Data: atom.Span.String(),
 		Attr: []html.Attribute{},
 	}
-	if class != "" {
-		span.Attr = append(span.Attr, html.Attribute{Key: "class", Val: class})
-	}
+	span.Attr = append(span.Attr, ctx.RenderInternal.NodeSafeAttr("class", "emoji"))
 	if name != "" {
 		span.Attr = append(span.Attr, html.Attribute{Key: "aria-label", Val: name})
 	}
@@ -35,13 +33,13 @@ func createEmoji(content, class, name string) *html.Node {
 	return span
 }
 
-func createCustomEmoji(alias string) *html.Node {
+func createCustomEmoji(ctx *RenderContext, alias string) *html.Node {
 	span := &html.Node{
 		Type: html.ElementNode,
 		Data: atom.Span.String(),
 		Attr: []html.Attribute{},
 	}
-	span.Attr = append(span.Attr, html.Attribute{Key: "class", Val: "emoji"})
+	span.Attr = append(span.Attr, ctx.RenderInternal.NodeSafeAttr("class", "emoji"))
 	span.Attr = append(span.Attr, html.Attribute{Key: "aria-label", Val: alias})
 
 	img := &html.Node{
@@ -77,7 +75,7 @@ func emojiShortCodeProcessor(ctx *RenderContext, node *html.Node) {
 		if converted == nil {
 			// check if this is a custom reaction
 			if _, exist := setting.UI.CustomEmojisMap[alias]; exist {
-				replaceContent(node, m[0], m[1], createCustomEmoji(alias))
+				replaceContent(node, m[0], m[1], createCustomEmoji(ctx, alias))
 				node = node.NextSibling.NextSibling
 				start = 0
 				continue
@@ -85,7 +83,7 @@ func emojiShortCodeProcessor(ctx *RenderContext, node *html.Node) {
 			continue
 		}
 
-		replaceContent(node, m[0], m[1], createEmoji(converted.Emoji, "emoji", converted.Description))
+		replaceContent(node, m[0], m[1], createEmoji(ctx, converted.Emoji, converted.Description))
 		node = node.NextSibling.NextSibling
 		start = 0
 	}
@@ -107,7 +105,7 @@ func emojiProcessor(ctx *RenderContext, node *html.Node) {
 		start = m[1]
 		val := emoji.FromCode(codepoint)
 		if val != nil {
-			replaceContent(node, m[0], m[1], createEmoji(codepoint, "emoji", val.Description))
+			replaceContent(node, m[0], m[1], createEmoji(ctx, codepoint, val.Description))
 			node = node.NextSibling.NextSibling
 			start = 0
 		}
diff --git a/modules/markup/html_issue.go b/modules/markup/html_issue.go
index 2acf154ad2..7341af7eb6 100644
--- a/modules/markup/html_issue.go
+++ b/modules/markup/html_issue.go
@@ -57,10 +57,10 @@ func fullIssuePatternProcessor(ctx *RenderContext, node *html.Node) {
 		matchRepo := linkParts[len(linkParts)-3]
 
 		if matchOrg == ctx.Metas["user"] && matchRepo == ctx.Metas["repo"] {
-			replaceContent(node, m[0], m[1], createLink(link, text, "ref-issue"))
+			replaceContent(node, m[0], m[1], createLink(ctx, link, text, "ref-issue"))
 		} else {
 			text = matchOrg + "/" + matchRepo + text
-			replaceContent(node, m[0], m[1], createLink(link, text, "ref-issue"))
+			replaceContent(node, m[0], m[1], createLink(ctx, link, text, "ref-issue"))
 		}
 		node = node.NextSibling.NextSibling
 	}
@@ -129,16 +129,16 @@ func issueIndexPatternProcessor(ctx *RenderContext, node *html.Node) {
 				log.Error("unable to expand template vars for ref %s, err: %v", ref.Issue, err)
 			}
 
-			link = createLink(res, reftext, "ref-issue ref-external-issue")
+			link = createLink(ctx, res, reftext, "ref-issue ref-external-issue")
 		} else {
 			// Path determines the type of link that will be rendered. It's unknown at this point whether
 			// the linked item is actually a PR or an issue. Luckily it's of no real consequence because
 			// Gitea will redirect on click as appropriate.
 			issuePath := util.Iif(ref.IsPull, "pulls", "issues")
 			if ref.Owner == "" {
-				link = createLink(util.URLJoin(ctx.Links.Prefix(), ctx.Metas["user"], ctx.Metas["repo"], issuePath, ref.Issue), reftext, "ref-issue")
+				link = createLink(ctx, util.URLJoin(ctx.Links.Prefix(), ctx.Metas["user"], ctx.Metas["repo"], issuePath, ref.Issue), reftext, "ref-issue")
 			} else {
-				link = createLink(util.URLJoin(ctx.Links.Prefix(), ref.Owner, ref.Name, issuePath, ref.Issue), reftext, "ref-issue")
+				link = createLink(ctx, util.URLJoin(ctx.Links.Prefix(), ref.Owner, ref.Name, issuePath, ref.Issue), reftext, "ref-issue")
 			}
 		}
 
@@ -151,7 +151,7 @@ func issueIndexPatternProcessor(ctx *RenderContext, node *html.Node) {
 		// Decorate action keywords if actionable
 		var keyword *html.Node
 		if references.IsXrefActionable(ref, hasExtTrackFormat) {
-			keyword = createKeyword(node.Data[ref.ActionLocation.Start:ref.ActionLocation.End])
+			keyword = createKeyword(ctx, node.Data[ref.ActionLocation.Start:ref.ActionLocation.End])
 		} else {
 			keyword = &html.Node{
 				Type: html.TextNode,
@@ -177,7 +177,7 @@ func commitCrossReferencePatternProcessor(ctx *RenderContext, node *html.Node) {
 		}
 
 		reftext := ref.Owner + "/" + ref.Name + "@" + base.ShortSha(ref.CommitSha)
-		link := createLink(util.URLJoin(ctx.Links.Prefix(), ref.Owner, ref.Name, "commit", ref.CommitSha), reftext, "commit")
+		link := createLink(ctx, util.URLJoin(ctx.Links.Prefix(), ref.Owner, ref.Name, "commit", ref.CommitSha), reftext, "commit")
 
 		replaceContent(node, ref.RefLocation.Start, ref.RefLocation.End, link)
 		node = node.NextSibling.NextSibling
diff --git a/modules/markup/html_link.go b/modules/markup/html_link.go
index b7562d0aa6..32aa7dc614 100644
--- a/modules/markup/html_link.go
+++ b/modules/markup/html_link.go
@@ -189,13 +189,13 @@ func shortLinkProcessor(ctx *RenderContext, node *html.Node) {
 func linkProcessor(ctx *RenderContext, node *html.Node) {
 	next := node.NextSibling
 	for node != nil && node != next {
-		m := common.LinkRegex.FindStringIndex(node.Data)
+		m := common.GlobalVars().LinkRegex.FindStringIndex(node.Data)
 		if m == nil {
 			return
 		}
 
 		uri := node.Data[m[0]:m[1]]
-		replaceContent(node, m[0], m[1], createLink(uri, uri, "link"))
+		replaceContent(node, m[0], m[1], createLink(ctx, uri, uri, "" /*link*/))
 		node = node.NextSibling.NextSibling
 	}
 }
@@ -204,7 +204,7 @@ func linkProcessor(ctx *RenderContext, node *html.Node) {
 func descriptionLinkProcessor(ctx *RenderContext, node *html.Node) {
 	next := node.NextSibling
 	for node != nil && node != next {
-		m := common.LinkRegex.FindStringIndex(node.Data)
+		m := common.GlobalVars().LinkRegex.FindStringIndex(node.Data)
 		if m == nil {
 			return
 		}
diff --git a/modules/markup/html_mention.go b/modules/markup/html_mention.go
index 3f0692e05f..f7e2ad50f1 100644
--- a/modules/markup/html_mention.go
+++ b/modules/markup/html_mention.go
@@ -33,7 +33,7 @@ func mentionProcessor(ctx *RenderContext, node *html.Node) {
 		if ok && strings.Contains(mention, "/") {
 			mentionOrgAndTeam := strings.Split(mention, "/")
 			if mentionOrgAndTeam[0][1:] == ctx.Metas["org"] && strings.Contains(teams, ","+strings.ToLower(mentionOrgAndTeam[1])+",") {
-				replaceContent(node, loc.Start, loc.End, createLink(util.URLJoin(ctx.Links.Prefix(), "org", ctx.Metas["org"], "teams", mentionOrgAndTeam[1]), mention, "mention"))
+				replaceContent(node, loc.Start, loc.End, createLink(ctx, util.URLJoin(ctx.Links.Prefix(), "org", ctx.Metas["org"], "teams", mentionOrgAndTeam[1]), mention, "" /*mention*/))
 				node = node.NextSibling.NextSibling
 				start = 0
 				continue
@@ -44,7 +44,7 @@ func mentionProcessor(ctx *RenderContext, node *html.Node) {
 		mentionedUsername := mention[1:]
 
 		if DefaultProcessorHelper.IsUsernameMentionable != nil && DefaultProcessorHelper.IsUsernameMentionable(ctx.Ctx, mentionedUsername) {
-			replaceContent(node, loc.Start, loc.End, createLink(util.URLJoin(ctx.Links.Prefix(), mentionedUsername), mention, "mention"))
+			replaceContent(node, loc.Start, loc.End, createLink(ctx, util.URLJoin(ctx.Links.Prefix(), mentionedUsername), mention, "" /*mention*/))
 			node = node.NextSibling.NextSibling
 			start = 0
 		} else {
diff --git a/modules/markup/internal/finalprocessor.go b/modules/markup/internal/finalprocessor.go
new file mode 100644
index 0000000000..14d46a161f
--- /dev/null
+++ b/modules/markup/internal/finalprocessor.go
@@ -0,0 +1,30 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package internal
+
+import (
+	"bytes"
+	"io"
+)
+
+type finalProcessor struct {
+	renderInternal *RenderInternal
+
+	output io.Writer
+	buf    bytes.Buffer
+}
+
+func (p *finalProcessor) Write(data []byte) (int, error) {
+	p.buf.Write(data)
+	return len(data), nil
+}
+
+func (p *finalProcessor) Close() error {
+	// TODO: reading the whole markdown isn't a problem at the moment,
+	// because "postProcess" already does so. In the future we could optimize the code to process data on the fly.
+	buf := p.buf.Bytes()
+	buf = bytes.ReplaceAll(buf, []byte(` data-attr-class="`+p.renderInternal.secureIDPrefix), []byte(` class="`))
+	_, err := p.output.Write(buf)
+	return err
+}
diff --git a/modules/markup/internal/internal_test.go b/modules/markup/internal/internal_test.go
new file mode 100644
index 0000000000..98ff3bc079
--- /dev/null
+++ b/modules/markup/internal/internal_test.go
@@ -0,0 +1,61 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package internal
+
+import (
+	"bytes"
+	"html/template"
+	"io"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestRenderInternal(t *testing.T) {
+	cases := []struct {
+		input, protected, recovered string
+	}{
+		{
+			input:     `<div class="test">class="content"</div>`,
+			protected: `<div data-attr-class="sec:test">class="content"</div>`,
+			recovered: `<div class="test">class="content"</div>`,
+		},
+		{
+			input:     "<div\nclass=\"test\" data-xxx></div>",
+			protected: `<div data-attr-class="sec:test" data-xxx></div>`,
+			recovered: `<div class="test" data-xxx></div>`,
+		},
+	}
+	for _, c := range cases {
+		var r RenderInternal
+		out := &bytes.Buffer{}
+		in := r.init("sec", out)
+		protected := r.ProtectSafeAttrs(template.HTML(c.input))
+		assert.EqualValues(t, c.protected, protected)
+		_, _ = io.WriteString(in, string(protected))
+		_ = in.Close()
+		assert.EqualValues(t, c.recovered, out.String())
+	}
+
+	var r1, r2 RenderInternal
+	protected := r1.ProtectSafeAttrs(`<div class="test"></div>`)
+	assert.EqualValues(t, `<div class="test"></div>`, protected, "non-initialized RenderInternal should not protect any attributes")
+	_ = r1.init("sec", nil)
+	protected = r1.ProtectSafeAttrs(`<div class="test"></div>`)
+	assert.EqualValues(t, `<div data-attr-class="sec:test"></div>`, protected)
+	assert.EqualValues(t, "data-attr-class", r1.SafeAttr("class"))
+	assert.EqualValues(t, "sec:val", r1.SafeValue("val"))
+	recovered, ok := r1.RecoverProtectedValue("sec:val")
+	assert.True(t, ok)
+	assert.EqualValues(t, "val", recovered)
+	recovered, ok = r1.RecoverProtectedValue("other:val")
+	assert.False(t, ok)
+	assert.Empty(t, recovered)
+
+	out2 := &bytes.Buffer{}
+	in2 := r2.init("sec-other", out2)
+	_, _ = io.WriteString(in2, string(protected))
+	_ = in2.Close()
+	assert.EqualValues(t, `<div data-attr-class="sec:test"></div>`, out2.String(), "different secureID should not recover the value")
+}
diff --git a/modules/markup/internal/renderinternal.go b/modules/markup/internal/renderinternal.go
new file mode 100644
index 0000000000..4775fecfc7
--- /dev/null
+++ b/modules/markup/internal/renderinternal.go
@@ -0,0 +1,82 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package internal
+
+import (
+	"crypto/rand"
+	"encoding/base64"
+	"html/template"
+	"io"
+	"regexp"
+	"strings"
+	"sync"
+
+	"code.gitea.io/gitea/modules/htmlutil"
+
+	"golang.org/x/net/html"
+)
+
+var reAttrClass = sync.OnceValue[*regexp.Regexp](func() *regexp.Regexp {
+	// TODO: it isn't a problem at the moment because our HTML contents are always well constructed
+	return regexp.MustCompile(`(<[^>]+)\s+class="([^"]+)"([^>]*>)`)
+})
+
+// RenderInternal also works without initialization
+// If no initialization (no secureID), it will not protect any attributes and return the original name&value
+type RenderInternal struct {
+	secureID       string
+	secureIDPrefix string
+}
+
+func (r *RenderInternal) Init(output io.Writer) io.WriteCloser {
+	buf := make([]byte, 12)
+	_, err := rand.Read(buf)
+	if err != nil {
+		panic("unable to generate secure id")
+	}
+	return r.init(base64.URLEncoding.EncodeToString(buf), output)
+}
+
+func (r *RenderInternal) init(secID string, output io.Writer) io.WriteCloser {
+	r.secureID = secID
+	r.secureIDPrefix = r.secureID + ":"
+	return &finalProcessor{renderInternal: r, output: output}
+}
+
+func (r *RenderInternal) RecoverProtectedValue(v string) (string, bool) {
+	if !strings.HasPrefix(v, r.secureIDPrefix) {
+		return "", false
+	}
+	return v[len(r.secureIDPrefix):], true
+}
+
+func (r *RenderInternal) SafeAttr(name string) string {
+	if r.secureID == "" {
+		return name
+	}
+	return "data-attr-" + name
+}
+
+func (r *RenderInternal) SafeValue(val string) string {
+	if r.secureID == "" {
+		return val
+	}
+	return r.secureID + ":" + val
+}
+
+func (r *RenderInternal) NodeSafeAttr(attr, val string) html.Attribute {
+	return html.Attribute{Key: r.SafeAttr(attr), Val: r.SafeValue(val)}
+}
+
+func (r *RenderInternal) ProtectSafeAttrs(content template.HTML) template.HTML {
+	if r.secureID == "" {
+		return content
+	}
+	return template.HTML(reAttrClass().ReplaceAllString(string(content), `$1 data-attr-class="`+r.secureIDPrefix+`$2"$3`))
+}
+
+func (r *RenderInternal) FormatWithSafeAttrs(w io.Writer, fmt string, a ...any) error {
+	_, err := w.Write([]byte(r.ProtectSafeAttrs(htmlutil.HTMLFormat(fmt, a...))))
+	return err
+}
diff --git a/modules/markup/markdown/ast.go b/modules/markup/markdown/ast.go
index 624c35d945..ca165b1ba0 100644
--- a/modules/markup/markdown/ast.go
+++ b/modules/markup/markdown/ast.go
@@ -34,13 +34,6 @@ func NewDetails() *Details {
 	}
 }
 
-// IsDetails returns true if the given node implements the Details interface,
-// otherwise false.
-func IsDetails(node ast.Node) bool {
-	_, ok := node.(*Details)
-	return ok
-}
-
 // Summary is a block that contains the summary of details block
 type Summary struct {
 	ast.BaseBlock
@@ -66,13 +59,6 @@ func NewSummary() *Summary {
 	}
 }
 
-// IsSummary returns true if the given node implements the Summary interface,
-// otherwise false.
-func IsSummary(node ast.Node) bool {
-	_, ok := node.(*Summary)
-	return ok
-}
-
 // TaskCheckBoxListItem is a block that represents a list item of a markdown block with a checkbox
 type TaskCheckBoxListItem struct {
 	*ast.ListItem
@@ -103,14 +89,7 @@ func NewTaskCheckBoxListItem(listItem *ast.ListItem) *TaskCheckBoxListItem {
 	}
 }
 
-// IsTaskCheckBoxListItem returns true if the given node implements the TaskCheckBoxListItem interface,
-// otherwise false.
-func IsTaskCheckBoxListItem(node ast.Node) bool {
-	_, ok := node.(*TaskCheckBoxListItem)
-	return ok
-}
-
-// Icon is an inline for a fomantic icon
+// Icon is an inline for a Fomantic UI icon
 type Icon struct {
 	ast.BaseInline
 	Name []byte
@@ -139,13 +118,6 @@ func NewIcon(name string) *Icon {
 	}
 }
 
-// IsIcon returns true if the given node implements the Icon interface,
-// otherwise false.
-func IsIcon(node ast.Node) bool {
-	_, ok := node.(*Icon)
-	return ok
-}
-
 // ColorPreview is an inline for a color preview
 type ColorPreview struct {
 	ast.BaseInline
diff --git a/modules/markup/markdown/goldmark.go b/modules/markup/markdown/goldmark.go
index c837b21e78..47dcfa8b5a 100644
--- a/modules/markup/markdown/goldmark.go
+++ b/modules/markup/markdown/goldmark.go
@@ -7,9 +7,11 @@ import (
 	"fmt"
 	"regexp"
 	"strings"
+	"sync"
 
 	"code.gitea.io/gitea/modules/container"
 	"code.gitea.io/gitea/modules/markup"
+	"code.gitea.io/gitea/modules/markup/internal"
 	"code.gitea.io/gitea/modules/setting"
 
 	"github.com/yuin/goldmark/ast"
@@ -23,11 +25,13 @@ import (
 
 // ASTTransformer is a default transformer of the goldmark tree.
 type ASTTransformer struct {
+	renderInternal *internal.RenderInternal
 	attentionTypes container.Set[string]
 }
 
-func NewASTTransformer() *ASTTransformer {
+func NewASTTransformer(renderInternal *internal.RenderInternal) *ASTTransformer {
 	return &ASTTransformer{
+		renderInternal: renderInternal,
 		attentionTypes: container.SetOf("note", "tip", "important", "warning", "caution"),
 	}
 }
@@ -109,12 +113,16 @@ func (g *ASTTransformer) Transform(node *ast.Document, reader text.Reader, pc pa
 	}
 }
 
-// NewHTMLRenderer creates a HTMLRenderer to render
-// in the gitea form.
-func NewHTMLRenderer(opts ...html.Option) renderer.NodeRenderer {
+// it is copied from old code, which is quite doubtful whether it is correct
+var reValidIconName = sync.OnceValue[*regexp.Regexp](func() *regexp.Regexp {
+	return regexp.MustCompile(`^[-\w]+$`) // old: regexp.MustCompile("^[a-z ]+$")
+})
+
+// NewHTMLRenderer creates a HTMLRenderer to render in the gitea form.
+func NewHTMLRenderer(renderInternal *internal.RenderInternal, opts ...html.Option) renderer.NodeRenderer {
 	r := &HTMLRenderer{
-		Config:      html.NewConfig(),
-		reValidName: regexp.MustCompile("^[a-z ]+$"),
+		renderInternal: renderInternal,
+		Config:         html.NewConfig(),
 	}
 	for _, opt := range opts {
 		opt.SetHTMLOption(&r.Config)
@@ -126,7 +134,7 @@ func NewHTMLRenderer(opts ...html.Option) renderer.NodeRenderer {
 // renders gitea specific features.
 type HTMLRenderer struct {
 	html.Config
-	reValidName *regexp.Regexp
+	renderInternal *internal.RenderInternal
 }
 
 // RegisterFuncs implements renderer.NodeRenderer.RegisterFuncs.
@@ -214,12 +222,13 @@ func (r *HTMLRenderer) renderIcon(w util.BufWriter, source []byte, node ast.Node
 		return ast.WalkContinue, nil
 	}
 
-	if !r.reValidName.MatchString(name) {
+	if !reValidIconName().MatchString(name) {
 		// skip this
 		return ast.WalkContinue, nil
 	}
 
-	_, err := w.WriteString(fmt.Sprintf(`<i class="icon %s"></i>`, name))
+	// FIXME: the "icon xxx" is from Fomantic UI, it's really questionable whether it still works correctly
+	err := r.renderInternal.FormatWithSafeAttrs(w, `<i class="icon %s"></i>`, name)
 	if err != nil {
 		return ast.WalkStop, err
 	}
diff --git a/modules/markup/markdown/markdown.go b/modules/markup/markdown/markdown.go
index 6af0deb27b..a3915ad439 100644
--- a/modules/markup/markdown/markdown.go
+++ b/modules/markup/markdown/markdown.go
@@ -9,7 +9,6 @@ import (
 	"html/template"
 	"io"
 	"strings"
-	"sync"
 
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/markup"
@@ -29,11 +28,6 @@ import (
 	"github.com/yuin/goldmark/util"
 )
 
-var (
-	specMarkdown     goldmark.Markdown
-	specMarkdownOnce sync.Once
-)
-
 var (
 	renderContextKey = parser.NewContextKey()
 	renderConfigKey  = parser.NewContextKey()
@@ -68,85 +62,95 @@ func newParserContext(ctx *markup.RenderContext) parser.Context {
 	return pc
 }
 
+type GlodmarkRender struct {
+	ctx *markup.RenderContext
+
+	goldmarkMarkdown goldmark.Markdown
+}
+
+func (r *GlodmarkRender) Convert(source []byte, writer io.Writer, opts ...parser.ParseOption) error {
+	return r.goldmarkMarkdown.Convert(source, writer, opts...)
+}
+
+func (r *GlodmarkRender) Renderer() renderer.Renderer {
+	return r.goldmarkMarkdown.Renderer()
+}
+
+func (r *GlodmarkRender) highlightingRenderer(w util.BufWriter, c highlighting.CodeBlockContext, entering bool) {
+	if entering {
+		language, _ := c.Language()
+		if language == nil {
+			language = []byte("text")
+		}
+
+		languageStr := string(language)
+
+		preClasses := []string{"code-block"}
+		if languageStr == "mermaid" || languageStr == "math" {
+			preClasses = append(preClasses, "is-loading")
+		}
+
+		err := r.ctx.RenderInternal.FormatWithSafeAttrs(w, `<pre class="%s">`, strings.Join(preClasses, " "))
+		if err != nil {
+			return
+		}
+
+		// include language-x class as part of commonmark spec
+		// the "display" class is used by "js/markup/math.js" to render the code element as a block
+		err = r.ctx.RenderInternal.FormatWithSafeAttrs(w, `<code class="chroma language-%s display">`, string(language))
+		if err != nil {
+			return
+		}
+	} else {
+		_, err := w.WriteString("</code></pre>")
+		if err != nil {
+			return
+		}
+	}
+}
+
 // SpecializedMarkdown sets up the Gitea specific markdown extensions
-func SpecializedMarkdown() goldmark.Markdown {
-	specMarkdownOnce.Do(func() {
-		specMarkdown = goldmark.New(
-			goldmark.WithExtensions(
-				extension.NewTable(
-					extension.WithTableCellAlignMethod(extension.TableCellAlignAttribute)),
-				extension.Strikethrough,
-				extension.TaskList,
-				extension.DefinitionList,
-				common.FootnoteExtension,
-				highlighting.NewHighlighting(
-					highlighting.WithFormatOptions(
-						chromahtml.WithClasses(true),
-						chromahtml.PreventSurroundingPre(true),
-					),
-					highlighting.WithWrapperRenderer(func(w util.BufWriter, c highlighting.CodeBlockContext, entering bool) {
-						if entering {
-							language, _ := c.Language()
-							if language == nil {
-								language = []byte("text")
-							}
-
-							languageStr := string(language)
-
-							preClasses := []string{"code-block"}
-							if languageStr == "mermaid" || languageStr == "math" {
-								preClasses = append(preClasses, "is-loading")
-							}
-
-							_, err := w.WriteString(`<pre class="` + strings.Join(preClasses, " ") + `">`)
-							if err != nil {
-								return
-							}
-
-							// include language-x class as part of commonmark spec
-							// the "display" class is used by "js/markup/math.js" to render the code element as a block
-							_, err = w.WriteString(`<code class="chroma language-` + string(language) + ` display">`)
-							if err != nil {
-								return
-							}
-						} else {
-							_, err := w.WriteString("</code></pre>")
-							if err != nil {
-								return
-							}
-						}
-					}),
-				),
-				math.NewExtension(
-					math.Enabled(setting.Markdown.EnableMath),
-				),
-				meta.Meta,
-			),
-			goldmark.WithParserOptions(
-				parser.WithAttribute(),
-				parser.WithAutoHeadingID(),
-				parser.WithASTTransformers(
-					util.Prioritized(NewASTTransformer(), 10000),
+func SpecializedMarkdown(ctx *markup.RenderContext) *GlodmarkRender {
+	// TODO: it could use a pool to cache the renderers to reuse them with different contexts
+	// at the moment it is fast enough (see the benchmarks)
+	r := &GlodmarkRender{ctx: ctx}
+	r.goldmarkMarkdown = goldmark.New(
+		goldmark.WithExtensions(
+			extension.NewTable(extension.WithTableCellAlignMethod(extension.TableCellAlignAttribute)),
+			extension.Strikethrough,
+			extension.TaskList,
+			extension.DefinitionList,
+			common.FootnoteExtension,
+			highlighting.NewHighlighting(
+				highlighting.WithFormatOptions(
+					chromahtml.WithClasses(true),
+					chromahtml.PreventSurroundingPre(true),
 				),
+				highlighting.WithWrapperRenderer(r.highlightingRenderer),
 			),
-			goldmark.WithRendererOptions(
-				html.WithUnsafe(),
-			),
-		)
-
-		// Override the original Tasklist renderer!
-		specMarkdown.Renderer().AddOptions(
-			renderer.WithNodeRenderers(
-				util.Prioritized(NewHTMLRenderer(), 10),
-			),
-		)
-	})
-	return specMarkdown
+			math.NewExtension(&ctx.RenderInternal, math.Enabled(setting.Markdown.EnableMath)),
+			meta.Meta,
+		),
+		goldmark.WithParserOptions(
+			parser.WithAttribute(),
+			parser.WithAutoHeadingID(),
+			parser.WithASTTransformers(util.Prioritized(NewASTTransformer(&ctx.RenderInternal), 10000)),
+		),
+		goldmark.WithRendererOptions(html.WithUnsafe()),
+	)
+
+	// Override the original Tasklist renderer!
+	r.goldmarkMarkdown.Renderer().AddOptions(
+		renderer.WithNodeRenderers(util.Prioritized(NewHTMLRenderer(&ctx.RenderInternal), 10)),
+	)
+
+	return r
 }
 
-// actualRender renders Markdown to HTML without handling special links.
-func actualRender(ctx *markup.RenderContext, input io.Reader, output io.Writer) error {
-	converter := SpecializedMarkdown()
+// render calls goldmark render to convert Markdown to HTML
+// NOTE: The output of this method MUST get sanitized separately!!!
+func render(ctx *markup.RenderContext, input io.Reader, output io.Writer) error {
+	converter := SpecializedMarkdown(ctx)
 	lw := &limitWriter{
 		w:     output,
 		limit: setting.UI.MaxDisplayFileSize * 3,
@@ -160,8 +164,8 @@ func actualRender(ctx *markup.RenderContext, input io.Reader, output io.Writer)
 		}
 
 		log.Warn("Unable to render markdown due to panic in goldmark: %v", err)
-		if log.IsDebug() {
-			log.Debug("Panic in markdown: %v\n%s", err, log.Stack(2))
+		if (!setting.IsProd && !setting.IsInTesting) || log.IsDebug() {
+			log.Error("Panic in markdown: %v\n%s", err, log.Stack(2))
 		}
 	}()
 
@@ -200,26 +204,6 @@ func actualRender(ctx *markup.RenderContext, input io.Reader, output io.Writer)
 	return nil
 }
 
-// Note: The output of this method must get sanitized.
-func render(ctx *markup.RenderContext, input io.Reader, output io.Writer) error {
-	defer func() {
-		err := recover()
-		if err == nil {
-			return
-		}
-
-		log.Warn("Unable to render markdown due to panic in goldmark - will return raw bytes")
-		if log.IsDebug() {
-			log.Debug("Panic in markdown: %v\n%s", err, log.Stack(2))
-		}
-		_, err = io.Copy(output, input)
-		if err != nil {
-			log.Error("io.Copy failed: %v", err)
-		}
-	}()
-	return actualRender(ctx, input, output)
-}
-
 // MarkupName describes markup's name
 var MarkupName = "markdown"
 
diff --git a/modules/markup/markdown/markdown_test.go b/modules/markup/markdown/markdown_test.go
index 780df8727f..e4889a75e5 100644
--- a/modules/markup/markdown/markdown_test.go
+++ b/modules/markup/markdown/markdown_test.go
@@ -1051,3 +1051,17 @@ func TestAttention(t *testing.T) {
 	// legacy GitHub style
 	test(`> **warning**`, renderAttention("warning", "octicon-alert")+"\n</blockquote>")
 }
+
+func BenchmarkSpecializedMarkdown(b *testing.B) {
+	// 240856	      4719 ns/op
+	for i := 0; i < b.N; i++ {
+		markdown.SpecializedMarkdown(&markup.RenderContext{})
+	}
+}
+
+func BenchmarkMarkdownRender(b *testing.B) {
+	// 23202	     50840 ns/op
+	for i := 0; i < b.N; i++ {
+		_, _ = markdown.RenderString(&markup.RenderContext{Ctx: context.Background()}, "https://example.com\n- a\n- b\n")
+	}
+}
diff --git a/modules/markup/markdown/math/block_renderer.go b/modules/markup/markdown/math/block_renderer.go
index 84817ef1e4..0d2a966102 100644
--- a/modules/markup/markdown/math/block_renderer.go
+++ b/modules/markup/markdown/math/block_renderer.go
@@ -4,17 +4,21 @@
 package math
 
 import (
+	"code.gitea.io/gitea/modules/markup/internal"
+
 	gast "github.com/yuin/goldmark/ast"
 	"github.com/yuin/goldmark/renderer"
 	"github.com/yuin/goldmark/util"
 )
 
 // BlockRenderer represents a renderer for math Blocks
-type BlockRenderer struct{}
+type BlockRenderer struct {
+	renderInternal *internal.RenderInternal
+}
 
 // NewBlockRenderer creates a new renderer for math Blocks
-func NewBlockRenderer() renderer.NodeRenderer {
-	return &BlockRenderer{}
+func NewBlockRenderer(renderInternal *internal.RenderInternal) renderer.NodeRenderer {
+	return &BlockRenderer{renderInternal: renderInternal}
 }
 
 // RegisterFuncs registers the renderer for math Blocks
@@ -33,7 +37,7 @@ func (r *BlockRenderer) writeLines(w util.BufWriter, source []byte, n gast.Node)
 func (r *BlockRenderer) renderBlock(w util.BufWriter, source []byte, node gast.Node, entering bool) (gast.WalkStatus, error) {
 	n := node.(*Block)
 	if entering {
-		_, _ = w.WriteString(`<pre class="code-block is-loading"><code class="chroma language-math display">`)
+		_ = r.renderInternal.FormatWithSafeAttrs(w, `<pre class="code-block is-loading"><code class="chroma language-math display">`)
 		r.writeLines(w, source, n)
 	} else {
 		_, _ = w.WriteString(`</code></pre>` + "\n")
diff --git a/modules/markup/markdown/math/inline_renderer.go b/modules/markup/markdown/math/inline_renderer.go
index 96848099cc..0cff4f1e74 100644
--- a/modules/markup/markdown/math/inline_renderer.go
+++ b/modules/markup/markdown/math/inline_renderer.go
@@ -6,17 +6,21 @@ package math
 import (
 	"bytes"
 
+	"code.gitea.io/gitea/modules/markup/internal"
+
 	"github.com/yuin/goldmark/ast"
 	"github.com/yuin/goldmark/renderer"
 	"github.com/yuin/goldmark/util"
 )
 
 // InlineRenderer is an inline renderer
-type InlineRenderer struct{}
+type InlineRenderer struct {
+	renderInternal *internal.RenderInternal
+}
 
 // NewInlineRenderer returns a new renderer for inline math
-func NewInlineRenderer() renderer.NodeRenderer {
-	return &InlineRenderer{}
+func NewInlineRenderer(renderInternal *internal.RenderInternal) renderer.NodeRenderer {
+	return &InlineRenderer{renderInternal: renderInternal}
 }
 
 func (r *InlineRenderer) renderInline(w util.BufWriter, source []byte, n ast.Node, entering bool) (ast.WalkStatus, error) {
@@ -25,7 +29,7 @@ func (r *InlineRenderer) renderInline(w util.BufWriter, source []byte, n ast.Nod
 		if _, ok := n.(*InlineBlock); ok {
 			extraClass = "display "
 		}
-		_, _ = w.WriteString(`<code class="language-math ` + extraClass + `is-loading">`)
+		_ = r.renderInternal.FormatWithSafeAttrs(w, `<code class="language-math %sis-loading">`, extraClass)
 		for c := n.FirstChild(); c != nil; c = c.NextSibling() {
 			segment := c.(*ast.Text).Segment
 			value := util.EscapeHTML(segment.Value(source))
diff --git a/modules/markup/markdown/math/math.go b/modules/markup/markdown/math/math.go
index 3d9f376bc6..7e8defcd4a 100644
--- a/modules/markup/markdown/math/math.go
+++ b/modules/markup/markdown/math/math.go
@@ -4,6 +4,8 @@
 package math
 
 import (
+	"code.gitea.io/gitea/modules/markup/internal"
+
 	"github.com/yuin/goldmark"
 	"github.com/yuin/goldmark/parser"
 	"github.com/yuin/goldmark/renderer"
@@ -12,6 +14,7 @@ import (
 
 // Extension is a math extension
 type Extension struct {
+	renderInternal    *internal.RenderInternal
 	enabled           bool
 	parseDollarInline bool
 	parseDollarBlock  bool
@@ -39,38 +42,10 @@ func Enabled(enable ...bool) Option {
 	})
 }
 
-// WithInlineDollarParser enables or disables the parsing of $...$
-func WithInlineDollarParser(enable ...bool) Option {
-	value := true
-	if len(enable) > 0 {
-		value = enable[0]
-	}
-	return extensionFunc(func(e *Extension) {
-		e.parseDollarInline = value
-	})
-}
-
-// WithBlockDollarParser enables or disables the parsing of $$...$$
-func WithBlockDollarParser(enable ...bool) Option {
-	value := true
-	if len(enable) > 0 {
-		value = enable[0]
-	}
-	return extensionFunc(func(e *Extension) {
-		e.parseDollarBlock = value
-	})
-}
-
-// Math represents a math extension with default rendered delimiters
-var Math = &Extension{
-	enabled:           true,
-	parseDollarBlock:  true,
-	parseDollarInline: true,
-}
-
 // NewExtension creates a new math extension with the provided options
-func NewExtension(opts ...Option) *Extension {
+func NewExtension(renderInternal *internal.RenderInternal, opts ...Option) *Extension {
 	r := &Extension{
+		renderInternal:    renderInternal,
 		enabled:           true,
 		parseDollarBlock:  true,
 		parseDollarInline: true,
@@ -102,7 +77,7 @@ func (e *Extension) Extend(m goldmark.Markdown) {
 	m.Parser().AddOptions(parser.WithInlineParsers(inlines...))
 
 	m.Renderer().AddOptions(renderer.WithNodeRenderers(
-		util.Prioritized(NewBlockRenderer(), 501),
-		util.Prioritized(NewInlineRenderer(), 502),
+		util.Prioritized(NewBlockRenderer(e.renderInternal), 501),
+		util.Prioritized(NewInlineRenderer(e.renderInternal), 502),
 	))
 }
diff --git a/modules/markup/markdown/meta_test.go b/modules/markup/markdown/meta_test.go
index 6949966328..278c33f1d2 100644
--- a/modules/markup/markdown/meta_test.go
+++ b/modules/markup/markdown/meta_test.go
@@ -11,10 +11,8 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
-/*
-IssueTemplate is a legacy to keep the unit tests working.
-Copied from structs.IssueTemplate, the original type has been changed a lot to support yaml template.
-*/
+// IssueTemplate is a legacy to keep the unit tests working.
+// Copied from structs.IssueTemplate, the original type has been changed a lot to support yaml template.
 type IssueTemplate struct {
 	Name   string   `json:"name" yaml:"name"`
 	Title  string   `json:"title" yaml:"title"`
diff --git a/modules/markup/markdown/transform_blockquote.go b/modules/markup/markdown/transform_blockquote.go
index 92dc500e69..2651d44a69 100644
--- a/modules/markup/markdown/transform_blockquote.go
+++ b/modules/markup/markdown/transform_blockquote.go
@@ -32,7 +32,8 @@ func (r *HTMLRenderer) renderAttention(w util.BufWriter, source []byte, node ast
 		default: // including "note"
 			octiconName = "info"
 		}
-		_, _ = w.WriteString(string(svg.RenderHTML("octicon-"+octiconName, 16, "attention-icon attention-"+n.AttentionType)))
+		svgHTML := svg.RenderHTML("octicon-"+octiconName, 16, "attention-icon attention-"+n.AttentionType)
+		_, _ = w.WriteString(string(r.renderInternal.ProtectSafeAttrs(svgHTML)))
 	}
 	return ast.WalkContinue, nil
 }
@@ -128,13 +129,13 @@ func (g *ASTTransformer) transformBlockquote(v *ast.Blockquote, reader text.Read
 	}
 
 	// color the blockquote
-	v.SetAttributeString("class", []byte("attention-header attention-"+attentionType))
+	v.SetAttributeString(g.renderInternal.SafeAttr("class"), []byte(g.renderInternal.SafeValue("attention-header attention-"+attentionType)))
 
 	// create an emphasis to make it bold
 	attentionParagraph := ast.NewParagraph()
 	g.applyElementDir(attentionParagraph)
 	emphasis := ast.NewEmphasis(2)
-	emphasis.SetAttributeString("class", []byte("attention-"+attentionType))
+	emphasis.SetAttributeString(g.renderInternal.SafeAttr("class"), []byte(g.renderInternal.SafeValue("attention-"+attentionType)))
 
 	attentionAstString := ast.NewString([]byte(cases.Title(language.English).String(attentionType)))
 
diff --git a/modules/markup/markdown/transform_codespan.go b/modules/markup/markdown/transform_codespan.go
index ff7d24eec9..bccc43aad2 100644
--- a/modules/markup/markdown/transform_codespan.go
+++ b/modules/markup/markdown/transform_codespan.go
@@ -5,7 +5,6 @@ package markdown
 
 import (
 	"bytes"
-	"fmt"
 	"strings"
 
 	"code.gitea.io/gitea/modules/markup"
@@ -40,7 +39,7 @@ func (r *HTMLRenderer) renderCodeSpan(w util.BufWriter, source []byte, n ast.Nod
 					r.Writer.RawWrite(w, value)
 				}
 			case *ColorPreview:
-				_, _ = w.WriteString(fmt.Sprintf(`<span class="color-preview" style="background-color: %v"></span>`, string(v.Color)))
+				_ = r.renderInternal.FormatWithSafeAttrs(w, `<span class="color-preview" style="background-color: %s"></span>`, string(v.Color))
 			}
 		}
 		return ast.WalkSkipChildren, nil
diff --git a/modules/markup/markdown/transform_list.go b/modules/markup/markdown/transform_list.go
index b982fd4a83..c89ad2f2cf 100644
--- a/modules/markup/markdown/transform_list.go
+++ b/modules/markup/markdown/transform_list.go
@@ -72,7 +72,7 @@ func (g *ASTTransformer) transformList(_ *markup.RenderContext, v *ast.List, rc
 			}
 			newChild := NewTaskCheckBoxListItem(listItem)
 			newChild.IsChecked = taskCheckBox.IsChecked
-			newChild.SetAttributeString("class", []byte("task-list-item"))
+			newChild.SetAttributeString(g.renderInternal.SafeAttr("class"), []byte(g.renderInternal.SafeValue("task-list-item")))
 			segments := newChild.FirstChild().Lines()
 			if segments.Len() > 0 {
 				segment := segments.At(0)
diff --git a/modules/markup/render.go b/modules/markup/render.go
index 1977dc73f5..f05cb62626 100644
--- a/modules/markup/render.go
+++ b/modules/markup/render.go
@@ -9,14 +9,15 @@ import (
 	"io"
 	"net/url"
 	"strings"
-	"sync"
 
 	"code.gitea.io/gitea/modules/git"
 	"code.gitea.io/gitea/modules/gitrepo"
+	"code.gitea.io/gitea/modules/markup/internal"
 	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/util"
 
 	"github.com/yuin/goldmark/ast"
+	"golang.org/x/sync/errgroup"
 )
 
 type RenderMetaMode string
@@ -65,6 +66,8 @@ type RenderContext struct {
 	SidebarTocNode   ast.Node
 	RenderMetaAs     RenderMetaMode
 	InStandalonePage bool // used by external render. the router "/org/repo/render/..." will output the rendered content in a standalone page
+
+	RenderInternal internal.RenderInternal
 }
 
 // Cancel runs any cleanup functions that have been registered for this Ctx
@@ -156,59 +159,53 @@ sandbox="allow-scripts"
 	return err
 }
 
-func render(ctx *RenderContext, renderer Renderer, input io.Reader, output io.Writer) error {
-	var wg sync.WaitGroup
-	var err error
+func pipes() (io.ReadCloser, io.WriteCloser, func()) {
 	pr, pw := io.Pipe()
-	defer func() {
+	return pr, pw, func() {
 		_ = pr.Close()
 		_ = pw.Close()
-	}()
-
-	var pr2 io.ReadCloser
-	var pw2 io.WriteCloser
-
-	var sanitizerDisabled bool
-	if r, ok := renderer.(ExternalRenderer); ok {
-		sanitizerDisabled = r.SanitizerDisabled()
 	}
+}
 
-	if !sanitizerDisabled {
-		pr2, pw2 = io.Pipe()
-		defer func() {
-			_ = pr2.Close()
-			_ = pw2.Close()
-		}()
-
-		wg.Add(1)
-		go func() {
-			err = SanitizeReader(pr2, renderer.Name(), output)
-			_ = pr2.Close()
-			wg.Done()
-		}()
-	} else {
-		pw2 = util.NopCloser{Writer: output}
+func render(ctx *RenderContext, renderer Renderer, input io.Reader, output io.Writer) error {
+	finalProcessor := ctx.RenderInternal.Init(output)
+	defer finalProcessor.Close()
+
+	// input -> (pw1=pr1) -> renderer -> (pw2=pr2) -> SanitizeReader -> finalProcessor -> output
+	// no sanitizer: input -> (pw1=pr1) -> renderer -> pw2(finalProcessor) -> output
+	pr1, pw1, close1 := pipes()
+	defer close1()
+
+	eg, _ := errgroup.WithContext(ctx.Ctx)
+	var pw2 io.WriteCloser = util.NopCloser{Writer: finalProcessor}
+
+	if r, ok := renderer.(ExternalRenderer); !ok || !r.SanitizerDisabled() {
+		var pr2 io.ReadCloser
+		var close2 func()
+		pr2, pw2, close2 = pipes()
+		defer close2()
+		eg.Go(func() error {
+			defer pr2.Close()
+			return SanitizeReader(pr2, renderer.Name(), finalProcessor)
+		})
 	}
 
-	wg.Add(1)
-	go func() {
+	eg.Go(func() (err error) {
 		if r, ok := renderer.(PostProcessRenderer); ok && r.NeedPostProcess() {
-			err = PostProcess(ctx, pr, pw2)
+			err = PostProcess(ctx, pr1, pw2)
 		} else {
-			_, err = io.Copy(pw2, pr)
+			_, err = io.Copy(pw2, pr1)
 		}
-		_ = pr.Close()
-		_ = pw2.Close()
-		wg.Done()
-	}()
+		_, _ = pr1.Close(), pw2.Close()
+		return err
+	})
 
-	if err1 := renderer.Render(ctx, input, pw); err1 != nil {
-		return err1
+	if err := renderer.Render(ctx, input, pw1); err != nil {
+		return err
 	}
-	_ = pw.Close()
+	_ = pw1.Close()
 
-	wg.Wait()
-	return err
+	return eg.Wait()
 }
 
 // Init initializes the render global variables
diff --git a/modules/markup/sanitizer_custom.go b/modules/markup/sanitizer_custom.go
index 7978973166..7f96556fd7 100644
--- a/modules/markup/sanitizer_custom.go
+++ b/modules/markup/sanitizer_custom.go
@@ -4,6 +4,9 @@
 package markup
 
 import (
+	"regexp"
+	"strings"
+
 	"code.gitea.io/gitea/modules/setting"
 
 	"github.com/microcosm-cc/bluemonday"
@@ -15,8 +18,11 @@ func (st *Sanitizer) addSanitizerRules(policy *bluemonday.Policy, rules []settin
 			policy.AllowDataURIImages()
 		}
 		if rule.Element != "" {
-			if rule.Regexp != nil {
-				policy.AllowAttrs(rule.AllowAttr).Matching(rule.Regexp).OnElements(rule.Element)
+			if rule.Regexp != "" {
+				if !strings.HasPrefix(rule.Regexp, "^") || !strings.HasSuffix(rule.Regexp, "$") {
+					panic("Markup sanitizer rule regexp must start with ^ and end with $ to be strict")
+				}
+				policy.AllowAttrs(rule.AllowAttr).Matching(regexp.MustCompile(rule.Regexp)).OnElements(rule.Element)
 			} else {
 				policy.AllowAttrs(rule.AllowAttr).OnElements(rule.Element)
 			}
diff --git a/modules/markup/sanitizer_default.go b/modules/markup/sanitizer_default.go
index 476ae5e26f..0fa54efd45 100644
--- a/modules/markup/sanitizer_default.go
+++ b/modules/markup/sanitizer_default.go
@@ -16,36 +16,11 @@ import (
 func (st *Sanitizer) createDefaultPolicy() *bluemonday.Policy {
 	policy := bluemonday.UGCPolicy()
 
-	// For JS code copy and Mermaid loading state
-	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^code-block( is-loading)?$`)).OnElements("pre")
-
-	// For code preview
-	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^code-preview-[-\w]+( file-content)?$`)).Globally()
-	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^lines-num$`)).OnElements("td")
-	policy.AllowAttrs("data-line-number").OnElements("span")
-	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^lines-code chroma$`)).OnElements("td")
-	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^code-inner$`)).OnElements("div")
-
-	// For code preview (unicode escape)
-	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^file-view( unicode-escaped)?$`)).OnElements("table")
-	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^lines-escape$`)).OnElements("td")
-	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^toggle-escape-button btn interact-bg$`)).OnElements("a") // don't use button, button might submit a form
-	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^(ambiguous-code-point|escaped-code-point|broken-code-point)$`)).OnElements("span")
-	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^char$`)).OnElements("span")
-	policy.AllowAttrs("data-tooltip-content", "data-escaped").OnElements("span")
-
-	// For color preview
-	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^color-preview$`)).OnElements("span")
-
-	// For attention
-	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^attention-header attention-\w+$`)).OnElements("blockquote")
-	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^attention-\w+$`)).OnElements("strong")
-	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^attention-icon attention-\w+ svg octicon-[\w-]+$`)).OnElements("svg")
-	policy.AllowAttrs("viewBox", "width", "height", "aria-hidden").OnElements("svg")
-	policy.AllowAttrs("fill-rule", "d").OnElements("path")
+	// NOTICE: DO NOT add special "class" regexp rules here anymore, use RenderInternal.SafeAttr instead
 
-	// For Chroma markdown plugin
-	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^(chroma )?language-[\w-]+( display)?( is-loading)?$`)).OnElements("code")
+	// General safe SVG attributes
+	policy.AllowAttrs("viewBox", "width", "height", "aria-hidden", "data-attr-class").OnElements("svg")
+	policy.AllowAttrs("fill-rule", "d").OnElements("path")
 
 	// Checkboxes
 	policy.AllowAttrs("type").Matching(regexp.MustCompile(`^checkbox$`)).OnElements("input")
@@ -66,28 +41,15 @@ func (st *Sanitizer) createDefaultPolicy() *bluemonday.Policy {
 		policy.AllowURLSchemeWithCustomPolicy("data", disallowScheme)
 	}
 
-	// Allow classes for anchors
-	policy.AllowAttrs("class").Matching(regexp.MustCompile(`ref-issue( ref-external-issue)?`)).OnElements("a")
-
-	// Allow classes for task lists
-	policy.AllowAttrs("class").Matching(regexp.MustCompile(`task-list-item`)).OnElements("li")
-
 	// Allow classes for org mode list item status.
 	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^(unchecked|checked|indeterminate)$`)).OnElements("li")
 
-	// Allow icons
-	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^icon(\s+[\p{L}\p{N}_-]+)+$`)).OnElements("i")
-
-	// Allow classes for emojis
-	policy.AllowAttrs("class").Matching(regexp.MustCompile(`emoji`)).OnElements("img")
-
-	// Allow icons, emojis, chroma syntax and keyword markup on span
-	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^((icon(\s+[\p{L}\p{N}_-]+)+)|(emoji)|(language-math display)|(language-math inline))$|^([a-z][a-z0-9]{0,2})$|^` + keywordClass + `$`)).OnElements("span")
-
 	// Allow 'color' and 'background-color' properties for the style attribute on text elements.
 	policy.AllowStyles("color", "background-color").OnElements("span", "p")
 
-	// Allow generally safe attributes
+	policy.AllowAttrs("src", "autoplay", "controls").OnElements("video")
+
+	// Allow generally safe attributes (reference: https://github.com/jch/html-pipeline)
 	generalSafeAttrs := []string{
 		"abbr", "accept", "accept-charset",
 		"accesskey", "action", "align", "alt",
@@ -106,10 +68,9 @@ func (st *Sanitizer) createDefaultPolicy() *bluemonday.Policy {
 		"selected", "shape", "size", "span",
 		"start", "summary", "tabindex", "target",
 		"title", "type", "usemap", "valign", "value",
-		"vspace", "width", "itemprop",
-		"data-markdown-generated-content",
+		"vspace", "width", "itemprop", "itemscope", "itemtype",
+		"data-markdown-generated-content", "data-attr-class",
 	}
-
 	generalSafeElements := []string{
 		"h1", "h2", "h3", "h4", "h5", "h6", "h7", "h8", "br", "b", "i", "strong", "em", "a", "pre", "code", "img", "tt",
 		"div", "ins", "del", "sup", "sub", "p", "ol", "ul", "table", "thead", "tbody", "tfoot", "blockquote", "label",
@@ -117,14 +78,8 @@ func (st *Sanitizer) createDefaultPolicy() *bluemonday.Policy {
 		"details", "caption", "figure", "figcaption",
 		"abbr", "bdo", "cite", "dfn", "mark", "small", "span", "time", "video", "wbr",
 	}
-
-	policy.AllowAttrs(generalSafeAttrs...).OnElements(generalSafeElements...)
-
-	policy.AllowAttrs("src", "autoplay", "controls").OnElements("video")
-
-	policy.AllowAttrs("itemscope", "itemtype").OnElements("div")
-
 	// FIXME: Need to handle longdesc in img but there is no easy way to do it
+	policy.AllowAttrs(generalSafeAttrs...).OnElements(generalSafeElements...)
 
 	// Custom keyword markup
 	defaultSanitizer.addSanitizerRules(policy, setting.ExternalSanitizerRules)
diff --git a/modules/markup/sanitizer_default_test.go b/modules/markup/sanitizer_default_test.go
index 20370509c1..c5c43695ea 100644
--- a/modules/markup/sanitizer_default_test.go
+++ b/modules/markup/sanitizer_default_test.go
@@ -19,7 +19,6 @@ func TestSanitizer(t *testing.T) {
 		// Code highlighting class
 		`<code class="random string"></code>`, `<code></code>`,
 		`<code class="language-random ui tab active menu attached animating sidebar following bar center"></code>`, `<code></code>`,
-		`<code class="language-go"></code>`, `<code class="language-go"></code>`,
 
 		// Input checkbox
 		`<input type="hidden">`, ``,
@@ -38,10 +37,8 @@ func TestSanitizer(t *testing.T) {
 		// <kbd> tags
 		`<kbd>Ctrl + C</kbd>`, `<kbd>Ctrl + C</kbd>`,
 		`<i class="dropdown icon">NAUGHTY</i>`, `<i>NAUGHTY</i>`,
-		`<i class="icon dropdown"></i>`, `<i class="icon dropdown"></i>`,
 		`<input type="checkbox" disabled=""/>unchecked`, `<input type="checkbox" disabled=""/>unchecked`,
 		`<span class="emoji dropdown">NAUGHTY</span>`, `<span>NAUGHTY</span>`,
-		`<span class="emoji">contents</span>`, `<span class="emoji">contents</span>`,
 
 		// Color property
 		`<span style="color: red">Hello World</span>`, `<span style="color: red">Hello World</span>`,
diff --git a/modules/setting/markup.go b/modules/setting/markup.go
index 6c2246342b..dfce8afa77 100644
--- a/modules/setting/markup.go
+++ b/modules/setting/markup.go
@@ -54,7 +54,7 @@ type MarkupRenderer struct {
 type MarkupSanitizerRule struct {
 	Element            string
 	AllowAttr          string
-	Regexp             *regexp.Regexp
+	Regexp             string
 	AllowDataURIImages bool
 }
 
@@ -117,15 +117,24 @@ func createMarkupSanitizerRule(name string, sec ConfigSection) (MarkupSanitizerR
 
 		regexpStr := sec.Key("REGEXP").Value()
 		if regexpStr != "" {
-			// Validate when parsing the config that this is a valid regular
-			// expression. Then we can use regexp.MustCompile(...) later.
-			compiled, err := regexp.Compile(regexpStr)
+			hasPrefix := strings.HasPrefix(regexpStr, "^")
+			hasSuffix := strings.HasSuffix(regexpStr, "$")
+			if !hasPrefix || !hasSuffix {
+				log.Error("In markup.%s: REGEXP must start with ^ and end with $ to be strict", name)
+				// to avoid breaking existing user configurations and satisfy the strict requirement in addSanitizerRules
+				if !hasPrefix {
+					regexpStr = "^.*" + regexpStr
+				}
+				if !hasSuffix {
+					regexpStr += ".*$"
+				}
+			}
+			_, err := regexp.Compile(regexpStr)
 			if err != nil {
 				log.Error("In markup.%s: REGEXP (%s) failed to compile: %v", name, regexpStr, err)
 				return rule, false
 			}
-
-			rule.Regexp = compiled
+			rule.Regexp = regexpStr
 		}
 
 		ok = true
diff --git a/modules/svg/svg.go b/modules/svg/svg.go
index 8132978cac..fded9d0873 100644
--- a/modules/svg/svg.go
+++ b/modules/svg/svg.go
@@ -9,7 +9,7 @@ import (
 	"path"
 	"strings"
 
-	gitea_html "code.gitea.io/gitea/modules/html"
+	gitea_html "code.gitea.io/gitea/modules/htmlutil"
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/public"
 )
diff --git a/modules/templates/helper.go b/modules/templates/helper.go
index 3ef11772dc..d5b32358da 100644
--- a/modules/templates/helper.go
+++ b/modules/templates/helper.go
@@ -10,12 +10,12 @@ import (
 	"html/template"
 	"net/url"
 	"reflect"
-	"slices"
 	"strings"
 	"time"
 
 	user_model "code.gitea.io/gitea/models/user"
 	"code.gitea.io/gitea/modules/base"
+	"code.gitea.io/gitea/modules/htmlutil"
 	"code.gitea.io/gitea/modules/markup"
 	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/svg"
@@ -39,7 +39,7 @@ func NewFuncMap() template.FuncMap {
 		"Iif":          iif,
 		"Eval":         evalTokens,
 		"SafeHTML":     safeHTML,
-		"HTMLFormat":   HTMLFormat,
+		"HTMLFormat":   htmlutil.HTMLFormat,
 		"HTMLEscape":   htmlEscape,
 		"QueryEscape":  queryEscape,
 		"JSEscape":     jsEscapeSafe,
@@ -184,23 +184,6 @@ func NewFuncMap() template.FuncMap {
 	}
 }
 
-func HTMLFormat(s string, rawArgs ...any) template.HTML {
-	args := slices.Clone(rawArgs)
-	for i, v := range args {
-		switch v := v.(type) {
-		case nil, bool, int, int8, int16, int32, int64, uint, uint8, uint16, uint32, uint64, float32, float64, template.HTML:
-			// for most basic types (including template.HTML which is safe), just do nothing and use it
-		case string:
-			args[i] = template.HTMLEscapeString(v)
-		case fmt.Stringer:
-			args[i] = template.HTMLEscapeString(v.String())
-		default:
-			args[i] = template.HTMLEscapeString(fmt.Sprint(v))
-		}
-	}
-	return template.HTML(fmt.Sprintf(s, args...))
-}
-
 // safeHTML render raw as HTML
 func safeHTML(s any) template.HTML {
 	switch v := s.(type) {
diff --git a/modules/templates/helper_test.go b/modules/templates/helper_test.go
index b9fabb7016..3e17e86c66 100644
--- a/modules/templates/helper_test.go
+++ b/modules/templates/helper_test.go
@@ -61,10 +61,6 @@ func TestJSEscapeSafe(t *testing.T) {
 	assert.EqualValues(t, `\u0026\u003C\u003E\'\"`, jsEscapeSafe(`&<>'"`))
 }
 
-func TestHTMLFormat(t *testing.T) {
-	assert.Equal(t, template.HTML("<a>&lt; < 1</a>"), HTMLFormat("<a>%s %s %d</a>", "<", template.HTML("<"), 1))
-}
-
 func TestSanitizeHTML(t *testing.T) {
 	assert.Equal(t, template.HTML(`<a href="/" rel="nofollow">link</a> xss <div>inline</div>`), SanitizeHTML(`<a href="/">link</a> <a href="javascript:">xss</a> <div style="dangerous">inline</div>`))
 }
diff --git a/modules/templates/util_avatar.go b/modules/templates/util_avatar.go
index afc1091516..f7dd408ee2 100644
--- a/modules/templates/util_avatar.go
+++ b/modules/templates/util_avatar.go
@@ -14,7 +14,7 @@ import (
 	"code.gitea.io/gitea/models/organization"
 	repo_model "code.gitea.io/gitea/models/repo"
 	user_model "code.gitea.io/gitea/models/user"
-	gitea_html "code.gitea.io/gitea/modules/html"
+	gitea_html "code.gitea.io/gitea/modules/htmlutil"
 	"code.gitea.io/gitea/modules/setting"
 )
 
diff --git a/modules/templates/util_render.go b/modules/templates/util_render.go
index 8e443446bd..5776eefced 100644
--- a/modules/templates/util_render.go
+++ b/modules/templates/util_render.go
@@ -16,6 +16,7 @@ import (
 
 	issues_model "code.gitea.io/gitea/models/issues"
 	"code.gitea.io/gitea/modules/emoji"
+	"code.gitea.io/gitea/modules/htmlutil"
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/markup"
 	"code.gitea.io/gitea/modules/markup/markdown"
@@ -140,7 +141,7 @@ func (ut *RenderUtils) RenderLabel(label *issues_model.Label) template.HTML {
 
 	if labelScope == "" {
 		// Regular label
-		return HTMLFormat(`<div class="ui label %s" style="color: %s !important; background-color: %s !important;" data-tooltip-content title="%s">%s</div>`,
+		return htmlutil.HTMLFormat(`<div class="ui label %s" style="color: %s !important; background-color: %s !important;" data-tooltip-content title="%s">%s</div>`,
 			extraCSSClasses, textColor, label.Color, descriptionText, ut.RenderEmoji(label.Name))
 	}
 
@@ -174,7 +175,7 @@ func (ut *RenderUtils) RenderLabel(label *issues_model.Label) template.HTML {
 	itemColor := "#" + hex.EncodeToString(itemBytes)
 	scopeColor := "#" + hex.EncodeToString(scopeBytes)
 
-	return HTMLFormat(`<span class="ui label %s scope-parent" data-tooltip-content title="%s">`+
+	return htmlutil.HTMLFormat(`<span class="ui label %s scope-parent" data-tooltip-content title="%s">`+
 		`<div class="ui label scope-left" style="color: %s !important; background-color: %s !important">%s</div>`+
 		`<div class="ui label scope-right" style="color: %s !important; background-color: %s !important">%s</div>`+
 		`</span>`,
diff --git a/modules/templates/util_render_test.go b/modules/templates/util_render_test.go
index 529507e7ea..cf6d839cbf 100644
--- a/modules/templates/util_render_test.go
+++ b/modules/templates/util_render_test.go
@@ -113,34 +113,34 @@ func TestRenderCommitBody(t *testing.T) {
 	}
 
 	expected := `/just/a/path.bin
-<a href="https://example.com/file.bin" class="link">https://example.com/file.bin</a>
+<a href="https://example.com/file.bin">https://example.com/file.bin</a>
 [local link](file.bin)
-[remote link](<a href="https://example.com" class="link">https://example.com</a>)
+[remote link](<a href="https://example.com">https://example.com</a>)
 [[local link|file.bin]]
-[[remote link|<a href="https://example.com" class="link">https://example.com</a>]]
+[[remote link|<a href="https://example.com">https://example.com</a>]]
 ![local image](image.jpg)
-![remote image](<a href="https://example.com/image.jpg" class="link">https://example.com/image.jpg</a>)
+![remote image](<a href="https://example.com/image.jpg">https://example.com/image.jpg</a>)
 [[local image|image.jpg]]
-[[remote link|<a href="https://example.com/image.jpg" class="link">https://example.com/image.jpg</a>]]
+[[remote link|<a href="https://example.com/image.jpg">https://example.com/image.jpg</a>]]
 <a href="https://example.com/user/repo/compare/88fc37a3c0a4dda553bdcfc80c178a58247f42fb...12fc37a3c0a4dda553bdcfc80c178a58247f42fb#hash" class="compare"><code class="nohighlight">88fc37a3c0...12fc37a3c0 (hash)</code></a>
 com 88fc37a3c0a4dda553bdcfc80c178a58247f42fb...12fc37a3c0a4dda553bdcfc80c178a58247f42fb pare
 <a href="https://example.com/user/repo/commit/88fc37a3c0a4dda553bdcfc80c178a58247f42fb" class="commit"><code class="nohighlight">88fc37a3c0</code></a>
 com 88fc37a3c0a4dda553bdcfc80c178a58247f42fb mit
 <span class="emoji" aria-label="thumbs up">👍</span>
-<a href="mailto:mail@domain.com" class="mailto">mail@domain.com</a>
-<a href="/mention-user" class="mention">@mention-user</a> test
+<a href="mailto:mail@domain.com">mail@domain.com</a>
+<a href="/mention-user">@mention-user</a> test
 <a href="/user13/repo11/issues/123" class="ref-issue">#123</a>
   space`
 	assert.EqualValues(t, expected, string(newTestRenderUtils().RenderCommitBody(testInput(), testMetas)))
 }
 
 func TestRenderCommitMessage(t *testing.T) {
-	expected := `space <a href="/mention-user" data-markdown-generated-content="" class="mention">@mention-user</a>  `
+	expected := `space <a href="/mention-user" data-markdown-generated-content="">@mention-user</a>  `
 	assert.EqualValues(t, expected, newTestRenderUtils().RenderCommitMessage(testInput(), testMetas))
 }
 
 func TestRenderCommitMessageLinkSubject(t *testing.T) {
-	expected := `<a href="https://example.com/link" class="muted">space </a><a href="/mention-user" data-markdown-generated-content="" class="mention">@mention-user</a>`
+	expected := `<a href="https://example.com/link" class="muted">space </a><a href="/mention-user" data-markdown-generated-content="">@mention-user</a>`
 	assert.EqualValues(t, expected, newTestRenderUtils().RenderCommitMessageLinkSubject(testInput(), "https://example.com/link", testMetas))
 }
 
diff --git a/routers/web/repo/wiki.go b/routers/web/repo/wiki.go
index 13f6b69493..2732a67e71 100644
--- a/routers/web/repo/wiki.go
+++ b/routers/web/repo/wiki.go
@@ -326,7 +326,7 @@ func renderViewPage(ctx *context.Context) (*git.Repository, *git.TreeEntry) {
 
 	if rctx.SidebarTocNode != nil {
 		sb := &strings.Builder{}
-		err = markdown.SpecializedMarkdown().Renderer().Render(sb, nil, rctx.SidebarTocNode)
+		err = markdown.SpecializedMarkdown(rctx).Renderer().Render(sb, nil, rctx.SidebarTocNode)
 		if err != nil {
 			log.Error("Failed to render wiki sidebar TOC: %v", err)
 		} else {
-- 
2.39.5