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50 lines
2.2 KiB
50 lines
2.2 KiB
11 months ago
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commit eddedbfc14916aa06fc01ff04b38aeb30ae2e625
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Author: John MacFarlane <jgm@berkeley.edu>
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Date: Thu Jul 20 09:26:38 2023 -0700
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Fix new variant of the vulnerability in CVE-2023-35936.
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Guilhem Moulin noticed that the fix to CVE-2023-35936 was incomplete.
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An attacker could get around it by double-encoding the malicious
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extension to create or override arbitrary files.
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$ echo '' >b.md
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$ .cabal/bin/pandoc b.md --extract-media=bar
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<p><img
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src="bar/2a0eaa89f43fada3e6c577beea4f2f8f53ab6a1d.lua+%2f%2e%2e%2f%2e%2e%2fb%2elua" /></p>
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$ cat b.lua
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print "hello"
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$ find bar
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bar/
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bar/2a0eaa89f43fada3e6c577beea4f2f8f53ab6a1d.lua+
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This commit adds a test case for this more complex attack and fixes
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the vulnerability. (The fix is quite simple: if the URL-unescaped
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filename or extension contains a '%', we just use the sha1 hash of the
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contents as the canonical name, just as we do if the filename contains
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'..'.)
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--- pandoc-2.14.0.3/src/Text/Pandoc/MediaBag.hs.orig 2024-03-22 16:40:07.874200094 +0800
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+++ pandoc-2.14.0.3/src/Text/Pandoc/MediaBag.hs 2024-03-22 16:42:13.289905373 +0800
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@@ -85,16 +85,17 @@
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newpath = if isRelative fp''
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&& isNothing uri
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&& not (".." `T.isInfixOf` fp')
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+ && '%' `notElem` fp''
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then fp''
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- else showDigest (sha1 contents) <> "." <> ext
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+ else showDigest (sha1 contents) <> ext
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fallback = case takeExtension fp'' of
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".gz" -> getMimeTypeDef $ dropExtension fp''
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_ -> getMimeTypeDef fp''
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mt = fromMaybe fallback mbMime
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path = maybe fp'' (unEscapeString . uriPath) uri
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ext = case takeExtension path of
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- '.':e -> e
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- _ -> maybe "" T.unpack $ extensionFromMimeType mt
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+ '.':e | '%' `notElem` e -> '.':e
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+ _ -> maybe "" (\x -> '.':T.unpack x) $ extensionFromMimeType mt
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-- | Lookup a media item in a 'MediaBag', returning mime type and contents.
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