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--[[
Copyright (c) 2019, Vsevolod Stakhov <vsevolod@highsecure.ru>
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.
]]--
--[[[
-- @module lua_magic/heuristics
-- This module contains heuristics for some specific cases
--]]
local rspamd_trie = require "rspamd_trie"
local rspamd_util = require "rspamd_util"
local lua_util = require "lua_util"
local bit = require "bit"
local fun = require "fun"
local N = "lua_magic"
local msoffice_trie
local msoffice_patterns = {
doc = {[[WordDocument]]},
xls = {[[Workbook]], [[Book]]},
ppt = {[[PowerPoint Document]], [[Current User]]},
vsd = {[[VisioDocument]]},
}
local msoffice_trie_clsid
local msoffice_clsids = {
doc = {[[0609020000000000c000000000000046]]},
xls = {[[1008020000000000c000000000000046]], [[2008020000000000c000000000000046]]},
ppt = {[[108d81649b4fcf1186ea00aa00b929e8]]},
msg = {[[46f0060000000000c000000000000046]], [[0b0d020000000000c000000000000046]]},
msi = {[[84100c0000000000c000000000000046]]},
}
local zip_trie
local zip_patterns = {
-- https://lists.oasis-open.org/archives/office/200505/msg00006.html
odt = {
[[mimetypeapplication/vnd\.oasis\.opendocument.text]],
[[mimetypeapplication/vnd\.oasis.opendocument\.image]],
[[mimetypeapplication/vnd\.oasis\.opendocument\.graphic]]
},
ods = {
[[mimetypeapplication/vnd\.oasis\.opendocument\.spreadsheet]],
[[mimetypeapplication/vnd\.oasis\.opendocument.formula]],
[[mimetypeapplication/vnd\.oasis\.opendocument\.chart]]
},
odp = {[[mimetypeapplication/vnd\.oasis\.opendocument\.presentation]]},
epub = {[[epub\+zip]]}
}
local txt_trie
local txt_patterns = {
html = {
[[(?i)\s*<html]],
[[(?i)\s*<\!DOCTYPE HTML]],
[[(?i)\s*<xml]],
[[(?i)\s*<body]],
[[(?i)\s*<table]],
[[(?i)\s*<a]],
[[(?i)\s*<p]],
[[(?i)\s*<div]],
[[(?i)\s*<span]],
},
csv = {
[[(?:[-a-zA-Z0-9_]+\s*,){2,}(?:[-a-zA-Z0-9_]+[\r\n])]]
},
js = {
[[\s*function\s*\(]],
},
}
-- Used to match pattern index and extension
local msoffice_clsid_indexes = {}
local msoffice_patterns_indexes = {}
local zip_patterns_indexes = {}
local txt_patterns_indexes = {}
local exports = {}
local function compile_tries()
local function compile_pats(patterns, indexes, transform_func)
local strs = {}
for ext,pats in pairs(patterns) do
for _,pat in ipairs(pats) do
-- These are utf16 strings in fact...
strs[#strs + 1] = transform_func(pat)
indexes[#indexes + 1] = ext
end
end
return rspamd_trie.create(strs, rspamd_trie.flags.re)
end
if not msoffice_trie then
-- Directory names
local function msoffice_pattern_transform(pat)
return '^' ..
table.concat(
fun.totable(
fun.map(function(c) return c .. [[\x{00}]] end,
fun.iter(pat))))
end
local function msoffice_clsid_transform(pat)
local hex_table = {}
for i=1,#pat,2 do
local subc = pat:sub(i, i + 1)
hex_table[#hex_table + 1] = string.format('\\x{%s}', subc)
end
return '^' .. table.concat(hex_table) .. '$'
end
-- Directory entries
msoffice_trie = compile_pats(msoffice_patterns, msoffice_patterns_indexes,
msoffice_pattern_transform)
-- Clsids
msoffice_trie_clsid = compile_pats(msoffice_clsids, msoffice_clsid_indexes,
msoffice_clsid_transform)
-- Misc zip patterns at the initial fragment
zip_trie = compile_pats(zip_patterns, zip_patterns_indexes,
function(pat) return pat end)
-- Text patterns at the initial fragment
txt_trie = compile_pats(txt_patterns, txt_patterns_indexes,
function(pat) return pat end)
end
end
-- Call immediately on require
compile_tries()
local function detect_ole_format(input, log_obj)
local inplen = #input
if inplen < 0x31 + 4 then
lua_util.debugm(N, log_obj, "short length: %s", inplen)
return nil
end
local bom,sec_size = rspamd_util.unpack('<I2<I2', input:span(29, 4))
if bom == 0xFFFE then
bom = '<'
else
lua_util.debugm(N, log_obj, "bom file!: %s", bom)
bom = '>'; sec_size = bit.bswap(sec_size)
end
if sec_size < 7 or sec_size > 31 then
lua_util.debugm(N, log_obj, "bad sec_size: %s", sec_size)
return nil
end
sec_size = 2 ^ sec_size
-- SecID of first sector of the directory stream
local directory_offset = (rspamd_util.unpack(bom .. 'I4', input:span(0x31, 4)))
* sec_size + 512 + 1
lua_util.debugm(N, log_obj, "directory: %s", directory_offset)
if inplen < directory_offset then
lua_util.debugm(N, log_obj, "short length: %s", inplen)
return nil
end
local function process_dir_entry(offset)
local dtype = input:at(offset + 66)
lua_util.debugm(N, log_obj, "dtype: %s, offset: %s", dtype, offset)
if dtype == 5 then
-- Extract clsid
local matches = msoffice_trie_clsid:match(input:span(offset + 80, 16))
if matches then
for n,_ in pairs(matches) do
if msoffice_clsid_indexes[n] then
lua_util.debugm(N, log_obj, "found valid clsid for %s",
msoffice_clsid_indexes[n])
return true,msoffice_clsid_indexes[n]
end
end
end
return true,nil
elseif dtype == 2 then
local matches = msoffice_trie:match(input:span(offset, 64))
if matches then
for n,_ in pairs(matches) do
if msoffice_patterns_indexes[n] then
return true,msoffice_patterns_indexes[n]
end
end
end
return true,nil
elseif dtype >= 0 and dtype < 5 then
-- Bad type
return true,nil
end
return false,nil
end
repeat
local res,ext = process_dir_entry(directory_offset)
if res and ext then
return ext,60
end
if not res then
break
end
directory_offset = directory_offset + 128
until directory_offset >= inplen
end
exports.ole_format_heuristic = detect_ole_format
local function process_top_detected(res)
local extensions = lua_util.keys(res)
if #extensions > 0 then
table.sort(extensions, function(ex1, ex2)
return res[ex1] > res[ex2]
end)
return extensions[1],res[extensions[1]]
end
return nil
end
local function detect_archive_flaw(part, arch, log_obj)
local arch_type = arch:get_type()
local res = {
docx = 0,
xlsx = 0,
pptx = 0,
jar = 0,
odt = 0,
odp = 0,
ods = 0
} -- ext + confidence pairs
-- General msoffice patterns
local function add_msoffice_confidence(incr)
res.docx = res.docx + incr
res.xlsx = res.xlsx + incr
res.pptx = res.pptx + incr
end
if arch_type == 'zip' then
-- Find specific files/folders in zip file
local files = arch:get_files() or {}
for _,file in ipairs(files) do
if file == '[Content_Types].xml' then
add_msoffice_confidence(10)
elseif file:sub(1, 3) == 'xl/' then
res.xlsx = res.xlsx + 30
elseif file:sub(1, 5) == 'word/' then
res.docx = res.docx + 30
elseif file:sub(1, 4) == 'ppt/' then
res.pptx = res.pptx + 30
elseif file == 'META-INF/MANIFEST.MF' then
res.jar = res.jar + 40
end
end
local ext,weight = process_top_detected(res)
if weight >= 40 then
return ext,weight
end
-- Apply misc Zip detection logic
local content = part:get_content()
if #content > 128 then
local start_span = content:span(1, 128)
local matches = zip_trie:match(start_span)
if matches then
for n,_ in pairs(matches) do
if zip_patterns_indexes[n] then
lua_util.debugm(N, log_obj, "found zip pattern for %s",
zip_patterns_indexes[n])
return zip_patterns_indexes[n],40
end
end
end
end
end
return arch_type:lower(),40
end
exports.mime_part_heuristic = function(part, log_obj)
if part:is_image() then
local img = part:get_image()
return img:get_type():lower(),60
end
if part:is_archive() then
local arch = part:get_archive()
return detect_archive_flaw(part, arch, log_obj)
end
return nil
end
exports.text_part_heuristic = function(part, log_obj)
-- We get some span of data and check it
local function is_span_text(span)
local function rough_utf8_check(b)
if b >= 127 then
if bit.band(b, 0xe0) == 0xc0 or bit.band(b, 0xf0) == 0xe0 or bit.band(b, 0xf8) == 0xf0 then
return true
end
return false
else
return true
end
end
-- Convert to string as LuaJIT can optimise string.sub (and fun.iter) but not C calls
local tlen = #span
local non_printable = 0
for _,b in ipairs(span:bytes()) do
if ((b < 0x20) and not (b == 0x0d or b == 0x0a or b == 0x09))
or (not rough_utf8_check(b)) then
non_printable = non_printable + 1
end
end
lua_util.debugm(N, log_obj, "text part check: %s printable, %s non-printable, %s total",
tlen - non_printable, non_printable, tlen)
if non_printable / tlen > 0.0625 then
return false
end
return true
end
local content = part:get_content()
local clen = #content
local is_text
if clen > 0 then
if clen > 80 * 3 then
-- Use chunks
is_text = is_span_text(content:span(1, 160)) and is_span_text(content:span(clen - 80, 80))
else
is_text = is_span_text(content)
end
if is_text then
-- Try patterns
local span_len = math.min(160, clen)
local start_span = content:span(1, span_len)
local matches = txt_trie:match(start_span)
local res = {}
if matches then
-- Require at least 2 occurrences of those patterns
for n,positions in pairs(matches) do
local ext = txt_patterns_indexes[n]
if ext then
res[ext] = (res[ext] or 0) + 20 * #positions
lua_util.debugm(N, log_obj, "found txt pattern for %s: %s",
ext, #positions)
end
end
if res.html and res.html >= 40 then
-- HTML has priority over something like js...
return 'html',res.html
end
local ext,weight = process_top_detected(res)
if weight and weight >= 40 then
return ext,weight
end
end
return 'txt',40
end
end
end
return exports
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