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|
--[[
Copyright (c) 2022, Vsevolod Stakhov <vsevolod@rspamd.com>
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
]]--
-- Misc rules
local E = {}
local fun = require "fun"
local rspamd_util = require "rspamd_util"
local rspamd_parsers = require "rspamd_parsers"
local rspamd_regexp = require "rspamd_regexp"
local lua_util = require "lua_util"
local bit = require "bit"
local rspamd_url = require "rspamd_url"
local url_flags_tab = rspamd_url.flags
-- Different text parts
rspamd_config.R_PARTS_DIFFER = {
callback = function(task)
local distance = task:get_mempool():get_variable('parts_distance', 'double')
if distance then
local nd = tonumber(distance)
-- ND is relation of different words to total words
if nd >= 0.5 then
local tw = task:get_mempool():get_variable('total_words', 'int')
if tw then
local score
if tw > 30 then
-- We are confident about difference
score = (nd - 0.5) * 2.0
else
-- We are not so confident about difference
score = (nd - 0.5)
end
task:insert_result('R_PARTS_DIFFER', score,
string.format('%.1f%%', tostring(100.0 * nd)))
end
end
end
return false
end,
score = 1.0,
description = 'Text and HTML parts differ',
group = 'body'
}
-- Date issues
local date_id = rspamd_config:register_symbol({
name = 'DATE_CB',
type = 'callback,mime',
callback = function(task)
local date_time = task:get_header('Date')
if date_time == nil or date_time == '' then
task:insert_result('MISSING_DATE', 1.0)
return
end
local dm, err = rspamd_parsers.parse_smtp_date(date_time)
if err then
task:insert_result('INVALID_DATE', 1.0)
return
end
local dt = task:get_date({ format = 'connect', gmt = true })
local date_diff = dt - dm
if date_diff > 86400 then
-- Older than a day
task:insert_result('DATE_IN_PAST', 1.0, tostring(math.floor(date_diff / 3600)))
elseif -date_diff > 7200 then
-- More than 2 hours in the future
task:insert_result('DATE_IN_FUTURE', 1.0, tostring(math.floor(-date_diff / 3600)))
end
end
})
rspamd_config:register_symbol({
name = 'MISSING_DATE',
score = 1.0,
description = 'Date header is missing',
group = 'headers',
type = 'virtual',
parent = date_id,
})
rspamd_config:register_symbol({
name = 'INVALID_DATE',
score = 1.5,
description = 'Malformed Date header',
group = 'headers',
type = 'virtual',
parent = date_id,
})
rspamd_config:register_symbol({
name = 'DATE_IN_FUTURE',
score = 4.0,
description = 'Message date is in the future',
group = 'headers',
type = 'virtual',
parent = date_id,
})
rspamd_config:register_symbol({
name = 'DATE_IN_PAST',
score = 1.0,
description = 'Message date is in the past',
group = 'headers',
type = 'virtual',
parent = date_id,
})
local obscured_id = rspamd_config:register_symbol {
callback = function(task)
local susp_urls = task:get_urls_filtered({ 'obscured', 'zw_spaces' })
if susp_urls and susp_urls[1] then
local obs_flag = url_flags_tab.obscured
local zw_flag = url_flags_tab.zw_spaces
for _, u in ipairs(susp_urls) do
local fl = u:get_flags_num()
if bit.band(fl, obs_flag) ~= 0 then
task:insert_result('R_SUSPICIOUS_URL', 1.0, u:get_host())
end
if bit.band(fl, zw_flag) ~= 0 then
task:insert_result('ZERO_WIDTH_SPACE_URL', 1.0, u:get_host())
end
end
end
return false
end,
name = 'R_SUSPICIOUS_URL',
score = 5.0,
one_shot = true,
description = 'A message has been identified to contain an obfuscated or suspicious URL',
group = 'url'
}
rspamd_config:register_symbol {
type = 'virtual',
name = 'ZERO_WIDTH_SPACE_URL',
score = 7.0,
one_shot = true,
description = 'Zero width space in URL',
group = 'url',
parent = obscured_id,
}
rspamd_config.ENVFROM_PRVS = {
callback = function(task)
--[[
Detect PRVS/BATV addresses to avoid FORGED_SENDER
https://en.wikipedia.org/wiki/Bounce_Address_Tag_Validation
Signature syntax:
prvs=TAG=USER@example.com BATV draft (https://tools.ietf.org/html/draft-levine-smtp-batv-01)
prvs=USER=TAG@example.com
btv1==TAG==USER@example.com Barracuda appliance
msprvs1=TAG=USER@example.com Sparkpost email delivery service
]]--
if not (task:has_from(1) and task:has_from(2)) then
return false
end
local envfrom = task:get_from(1)
local re_text = '^(?:(prvs|msprvs1)=([^=]+)=|btv1==[^=]+==)(.+@(.+))$'
local re = rspamd_regexp.create_cached(re_text)
local c = re:search(envfrom[1].addr:lower(), false, true)
if not c then
return false
end
local ef = c[1][4]
-- See if it matches the From header
local from = task:get_from(2)
if ef == from[1].addr:lower() then
return true
end
-- Check for prvs=USER=TAG@example.com
local t = c[1][2]
if t == 'prvs' then
local efr = c[1][3] .. '@' .. c[1][5]
if efr == from[1].addr:lower() then
return true
end
end
return false
end,
score = 0.0,
description = "Envelope From is a PRVS address that matches the From address",
group = 'headers',
type = 'mime',
}
rspamd_config.ENVFROM_VERP = {
callback = function(task)
if not (task:has_from(1) and task:has_recipients(1)) then
return false
end
local envfrom = task:get_from(1)
local envrcpts = task:get_recipients(1)
-- VERP only works for single recipient messages
if #envrcpts > 1 then
return false
end
-- Get recipient and compute VERP address
local rcpt = envrcpts[1].addr:lower()
local verp = rcpt:gsub('@', '=')
-- Get the user portion of the envfrom
local ef_user = envfrom[1].user:lower()
-- See if the VERP representation of the recipient appears in it
if ef_user:find(verp, 1, true)
and not ef_user:find('+caf_=' .. verp, 1, true) -- Google Forwarding
and not ef_user:find('^srs[01]=') -- SRS
then
return true
end
return false
end,
score = 0.0,
description = "Envelope From is a VERP address",
group = "headers",
type = 'mime',
}
local check_rcvd = rspamd_config:register_symbol {
name = 'CHECK_RCVD',
group = 'headers',
callback = function(task)
local rcvds = task:get_received_headers()
if not rcvds or #rcvds == 0 then
return false
end
local all_tls = fun.all(function(rc)
return rc.flags and rc.flags['ssl']
end, fun.filter(function(rc)
return rc.by_hostname and rc.by_hostname ~= 'localhost'
end, rcvds))
-- See if only the last hop was encrypted
if all_tls then
task:insert_result('RCVD_TLS_ALL', 1.0)
else
local rcvd = rcvds[1]
if rcvd.by_hostname and rcvd.by_hostname == 'localhost' then
-- Ignore artificial header from Rmilter
rcvd = rcvds[2] or {}
end
if rcvd.flags and rcvd.flags['ssl'] then
task:insert_result('RCVD_TLS_LAST', 1.0)
else
task:insert_result('RCVD_NO_TLS_LAST', 1.0)
end
end
local auth = fun.any(function(rc)
return rc.flags and rc.flags['authenticated']
end, rcvds)
if auth then
task:insert_result('RCVD_VIA_SMTP_AUTH', 1.0)
end
end,
type = 'callback,mime',
}
rspamd_config:register_symbol {
type = 'virtual',
parent = check_rcvd,
name = 'RCVD_TLS_ALL',
description = 'All hops used encrypted transports',
score = 0.0,
group = 'headers'
}
rspamd_config:register_symbol {
type = 'virtual',
parent = check_rcvd,
name = 'RCVD_TLS_LAST',
description = 'Last hop used encrypted transports',
score = 0.0,
group = 'headers'
}
rspamd_config:register_symbol {
type = 'virtual',
parent = check_rcvd,
name = 'RCVD_NO_TLS_LAST',
description = 'Last hop did not use encrypted transports',
score = 0.1,
group = 'headers'
}
rspamd_config:register_symbol {
type = 'virtual',
parent = check_rcvd,
name = 'RCVD_VIA_SMTP_AUTH',
-- NB This does not mean sender was authenticated; see task:get_user()
description = 'Authenticated hand-off was seen in Received headers',
score = 0.0,
group = 'headers'
}
rspamd_config.RCVD_HELO_USER = {
callback = function(task)
-- Check HELO argument from MTA
local helo = task:get_helo()
if (helo and helo:lower():find('^user$')) then
return true
end
-- Check Received headers
local rcvds = task:get_header_full('Received')
if not rcvds then
return false
end
for _, rcvd in ipairs(rcvds) do
local r = rcvd['decoded']:lower()
if (r:find("^%s*from%suser%s")) then
return true
end
if (r:find("helo[%s=]user[%s%)]")) then
return true
end
end
end,
description = 'HELO User spam pattern',
group = 'headers',
type = 'mime',
score = 3.0
}
rspamd_config.URI_COUNT_ODD = {
callback = function(task)
local ct = task:get_header('Content-Type')
if (ct and ct:lower():find('^multipart/alternative')) then
local urls = task:get_urls_filtered(nil, { 'subject', 'html_displayed', 'special' }) or {}
local nurls = fun.foldl(function(acc, val)
return acc + val:get_count()
end, 0, urls)
if nurls % 2 == 1 then
return true, 1.0, tostring(nurls)
end
end
end,
description = 'Odd number of URIs in multipart/alternative message',
score = 1.0,
group = 'url',
}
rspamd_config.HAS_ATTACHMENT = {
callback = function(task)
local parts = task:get_parts()
if parts and #parts > 1 then
for _, p in ipairs(parts) do
local cd = p:get_header('Content-Disposition')
if (cd and cd:lower():match('^attachment')) then
return true
end
end
end
end,
description = 'Message contains attachments',
group = 'body',
}
-- Requires freemail maps loaded in multimap
local function freemail_reply_neq_from(task)
if not task:has_symbol('FREEMAIL_REPLYTO') or not task:has_symbol('FREEMAIL_FROM') then
return false
end
local frt = task:get_symbol('FREEMAIL_REPLYTO')
local ff = task:get_symbol('FREEMAIL_FROM')
local frt_opts = frt[1]['options']
local ff_opts = ff[1]['options']
return (frt_opts and ff_opts and frt_opts[1] ~= ff_opts[1])
end
rspamd_config:register_symbol({
name = 'FREEMAIL_REPLYTO_NEQ_FROM_DOM',
callback = freemail_reply_neq_from,
description = 'The From and Reply-To addresses in the email are from different freemail services',
score = 3.0,
group = 'headers',
})
rspamd_config:register_dependency('FREEMAIL_REPLYTO_NEQ_FROM_DOM', 'FREEMAIL_REPLYTO')
rspamd_config:register_dependency('FREEMAIL_REPLYTO_NEQ_FROM_DOM', 'FREEMAIL_FROM')
rspamd_config.OMOGRAPH_URL = {
callback = function(task)
local urls = task:get_urls()
if urls then
local bad_omographs = 0
local single_bad_omograps = 0
local bad_urls = {}
local seen = {}
fun.each(function(u)
if u:is_phished() then
local h1 = u:get_host()
local h2 = u:get_phished()
if h2 then
-- Due to changes of the phished flag in 2.8
h2 = h2:get_host()
end
if h1 and h2 then
local selt = string.format('%s->%s', h1, h2)
if not seen[selt] and rspamd_util.is_utf_spoofed(h1, h2) then
bad_urls[#bad_urls + 1] = selt
bad_omographs = bad_omographs + 1
end
seen[selt] = true
end
end
if not u:is_html_displayed() then
local h = u:get_tld()
if h then
if not seen[h] and rspamd_util.is_utf_spoofed(h) then
bad_urls[#bad_urls + 1] = h
single_bad_omograps = single_bad_omograps + 1
end
seen[h] = true
end
end
end, urls)
if bad_omographs > 0 then
return true, 1.0, bad_urls
elseif single_bad_omograps > 0 then
return true, 0.5, bad_urls
end
end
return false
end,
score = 5.0,
group = 'url',
description = 'URL contains both latin and non-latin characters'
}
rspamd_config.URL_IN_SUBJECT = {
callback = function(task)
local urls = task:get_urls()
if urls then
for _, u in ipairs(urls) do
local flags = u:get_flags()
if flags.subject then
if flags.schemaless then
return true, 0.1, u:get_host()
end
local subject = task:get_subject()
if subject then
if tostring(u) == subject then
return true, 1.0, u:get_host()
end
end
return true, 0.25, u:get_host()
end
end
end
return false
end,
score = 4.0,
group = 'subject',
type = 'mime',
description = 'Subject contains URL'
}
local aliases_id = rspamd_config:register_symbol {
type = 'prefilter',
name = 'EMAIL_PLUS_ALIASES',
callback = function(task)
local function check_from(type)
if task:has_from(type) then
local addr = task:get_from(type)[1]
local na, tags = lua_util.remove_email_aliases(addr)
if na then
task:set_from(type, addr, 'alias')
task:insert_result('TAGGED_FROM', 1.0, fun.totable(
fun.filter(function(t)
return t and #t > 0
end, tags)))
end
end
end
check_from('smtp')
check_from('mime')
local function check_rcpt(type)
if task:has_recipients(type) then
local modified = false
local all_tags = {}
local addrs = task:get_recipients(type)
for _, addr in ipairs(addrs) do
local na, tags = lua_util.remove_email_aliases(addr)
if na then
modified = true
fun.each(function(t)
table.insert(all_tags, t)
end,
fun.filter(function(t)
return t and #t > 0
end, tags))
end
end
if modified then
task:set_recipients(type, addrs, 'alias')
task:insert_result('TAGGED_RCPT', 1.0, all_tags)
end
end
end
check_rcpt('smtp')
check_rcpt('mime')
end,
priority = lua_util.symbols_priorities.top + 1,
description = 'Removes plus aliases from the email',
group = 'headers',
}
rspamd_config:register_symbol {
type = 'virtual',
parent = aliases_id,
name = 'TAGGED_RCPT',
description = 'SMTP recipients have plus tags',
group = 'headers',
score = 0.0,
}
rspamd_config:register_symbol {
type = 'virtual',
parent = aliases_id,
name = 'TAGGED_FROM',
description = 'SMTP from has plus tags',
group = 'headers',
score = 0.0,
}
local check_from_display_name = rspamd_config:register_symbol {
type = 'callback,mime',
name = 'FROM_DISPLAY_CALLBACK',
callback = function(task)
local from = task:get_from(2)
if not (from and from[1] and from[1].name) then
return false
end
-- See if we can parse an email address from the name
local parsed = rspamd_parsers.parse_mail_address(from[1].name, task:get_mempool())
if not parsed then
return false
end
if not (parsed[1] and parsed[1]['addr']) then
return false
end
-- Make sure we did not mistake e.g. <something>@<name> for an email address
if not parsed[1]['domain'] or not parsed[1]['domain']:find('%.') then
return false
end
-- See if the parsed domains differ
if not rspamd_util.strequal_caseless(from[1]['domain'], parsed[1]['domain']) then
-- See if the destination domain is the same as the spoof
local mto = task:get_recipients(2)
local sto = task:get_recipients(1)
if mto then
for _, to in ipairs(mto) do
if to['domain'] ~= '' and rspamd_util.strequal_caseless(to['domain'], parsed[1]['domain']) then
task:insert_result('SPOOF_DISPLAY_NAME', 1.0, from[1]['domain'], parsed[1]['domain'])
return false
end
end
end
if sto then
for _, to in ipairs(sto) do
if to['domain'] ~= '' and rspamd_util.strequal_caseless(to['domain'], parsed[1]['domain']) then
task:insert_result('SPOOF_DISPLAY_NAME', 1.0, from[1]['domain'], parsed[1]['domain'])
return false
end
end
end
task:insert_result('FROM_NEQ_DISPLAY_NAME', 1.0, from[1]['domain'], parsed[1]['domain'])
end
return false
end,
group = 'headers',
}
rspamd_config:register_symbol {
type = 'virtual',
parent = check_from_display_name,
name = 'SPOOF_DISPLAY_NAME',
description = 'Display name is being used to spoof and trick the recipient',
group = 'headers',
score = 8.0,
}
rspamd_config:register_symbol {
type = 'virtual',
parent = check_from_display_name,
name = 'FROM_NEQ_DISPLAY_NAME',
group = 'headers',
description = 'Display name contains an email address different to the From address',
score = 4.0,
}
rspamd_config.SPOOF_REPLYTO = {
callback = function(task)
-- First check for a Reply-To header
local rt = task:get_header_full('Reply-To')
if not rt or not rt[1] then
return false
end
-- Get From and To headers
rt = rt[1]['value']
local from = task:get_from(2)
local to = task:get_recipients(2)
if not (from and from[1] and from[1].addr) then
return false
end
if (to and to[1] and to[1].addr) then
-- Handle common case for Web Contact forms of From = To
if rspamd_util.strequal_caseless(from[1].addr, to[1].addr) then
return false
end
end
-- SMTP recipients must contain From domain
to = task:get_recipients(1)
if not to then
return false
end
-- Try mitigate some possible FPs on mailing list posts
if #to == 1 and rspamd_util.strequal_caseless(to[1].addr, from[1].addr) then
return false
end
local found_fromdom = false
for _, t in ipairs(to) do
if rspamd_util.strequal_caseless(t.domain, from[1].domain) then
found_fromdom = true
break
end
end
if not found_fromdom then
return false
end
-- Parse Reply-To header
local parsed = ((rspamd_parsers.parse_mail_address(rt, task:get_mempool()) or E)[1] or E).domain
if not parsed then
return false
end
-- Reply-To domain must be different to From domain
if not rspamd_util.strequal_caseless(parsed, from[1].domain) then
return true, from[1].domain, parsed
end
return false
end,
group = 'headers',
type = 'mime',
description = 'Reply-To is being used to spoof and trick the recipient to send an off-domain reply',
score = 6.0
}
rspamd_config.INFO_TO_INFO_LU = {
callback = function(task)
if not task:has_header('List-Unsubscribe') then
return false
end
local from = task:get_from('mime')
if not (from and from[1] and rspamd_util.strequal_caseless(from[1].user, 'info')) then
return false
end
local to = task:get_recipients('smtp')
if not to then
return false
end
local found = false
for _, r in ipairs(to) do
if rspamd_util.strequal_caseless(r['user'], 'info') then
found = true
end
end
if found then
return true
end
return false
end,
description = 'info@ From/To address with List-Unsubscribe headers',
group = 'headers',
score = 2.0,
type = 'mime',
}
-- Detects bad content-transfer-encoding for text parts
rspamd_config.R_BAD_CTE_7BIT = {
callback = function(task)
local tp = task:get_text_parts() or {}
for _, p in ipairs(tp) do
local cte = p:get_mimepart():get_cte() or ''
if cte ~= '8bit' and p:has_8bit_raw() then
local _, _, attrs = p:get_mimepart():get_type_full()
local mul = 1.0
local params = { cte }
if attrs then
if attrs.charset and attrs.charset:lower() == "utf-8" then
-- Penalise rule as people don't know that utf8 is surprisingly
-- eight bit encoding
mul = 0.3
table.insert(params, "utf8")
end
end
return true, mul, params
end
end
return false
end,
score = 3.5,
description = 'Detects bad Content-Transfer-Encoding for text parts',
group = 'headers',
type = 'mime',
}
local check_encrypted_name = rspamd_config:register_symbol {
name = 'BOGUS_ENCRYPTED_AND_TEXT',
callback = function(task)
local parts = task:get_parts() or {}
local seen_encrypted, seen_text
local opts = {}
local function check_part(part)
if part:is_multipart() then
local children = part:get_children() or {}
local text_kids = {}
for _, cld in ipairs(children) do
if cld:is_multipart() then
check_part(cld)
elseif cld:is_text() then
seen_text = true
text_kids[#text_kids + 1] = cld
else
local type, subtype, _ = cld:get_type_full()
if type:lower() == 'application' then
if string.find(subtype:lower(), 'pkcs7%-mime') then
-- S/MIME encrypted part
seen_encrypted = true
table.insert(opts, 'smime part')
task:insert_result('ENCRYPTED_SMIME', 1.0)
elseif string.find(subtype:lower(), 'pkcs7%-signature') then
task:insert_result('SIGNED_SMIME', 1.0)
elseif string.find(subtype:lower(), 'pgp%-encrypted') then
-- PGP/GnuPG encrypted part
seen_encrypted = true
table.insert(opts, 'pgp part')
task:insert_result('ENCRYPTED_PGP', 1.0)
elseif string.find(subtype:lower(), 'pgp%-signature') then
task:insert_result('SIGNED_PGP', 1.0)
end
end
end
if seen_text and seen_encrypted then
-- Ensure that our seen text is not really part of pgp #3205
for _, tp in ipairs(text_kids) do
local t, _ = tp:get_type()
seen_text = false -- reset temporary
if t and t == 'text' then
seen_text = true
break
end
end
end
end
end
end
for _, part in ipairs(parts) do
check_part(part)
end
if seen_text and seen_encrypted then
return true, 1.0, opts
end
return false
end,
score = 10.0,
description = 'Bogus mix of encrypted and text/html payloads',
group = 'mime_types',
}
rspamd_config:register_symbol {
type = 'virtual',
parent = check_encrypted_name,
name = 'ENCRYPTED_PGP',
description = 'Message is encrypted with PGP',
group = 'mime_types',
score = -0.5,
one_shot = true
}
rspamd_config:register_symbol {
type = 'virtual',
parent = check_encrypted_name,
name = 'ENCRYPTED_SMIME',
description = 'Message is encrypted with S/MIME',
group = 'mime_types',
score = -0.5,
one_shot = true
}
rspamd_config:register_symbol {
type = 'virtual',
parent = check_encrypted_name,
name = 'SIGNED_PGP',
description = 'Message is signed with PGP',
group = 'mime_types',
score = -2.0,
one_shot = true
}
rspamd_config:register_symbol {
type = 'virtual',
parent = check_encrypted_name,
name = 'SIGNED_SMIME',
description = 'Message is signed with S/MIME',
group = 'mime_types',
score = -2.0,
one_shot = true
}
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