95 lines
3.4 KiB
Diff
95 lines
3.4 KiB
Diff
From 69d1b3fc29677af8ade8dc15dba83f0589cb63d6 Mon Sep 17 00:00:00 2001
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From: Lasse Collin <lasse.collin@tukaani.org>
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Date: Tue, 29 Mar 2022 19:19:12 +0300
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Subject: [PATCH] xzgrep: Fix escaping of malicious filenames (ZDI-CAN-16587).
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Malicious filenames can make xzgrep to write to arbitrary files
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or (with a GNU sed extension) lead to arbitrary code execution.
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xzgrep from XZ Utils versions up to and including 5.2.5 are
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affected. 5.3.1alpha and 5.3.2alpha are affected as well.
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This patch works for all of them.
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This bug was inherited from gzip's zgrep. gzip 1.12 includes
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a fix for zgrep.
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The issue with the old sed script is that with multiple newlines,
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the N-command will read the second line of input, then the
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s-commands will be skipped because it's not the end of the
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file yet, then a new sed cycle starts and the pattern space
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is printed and emptied. So only the last line or two get escaped.
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One way to fix this would be to read all lines into the pattern
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space first. However, the included fix is even simpler: All lines
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except the last line get a backslash appended at the end. To ensure
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that shell command substitution doesn't eat a possible trailing
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newline, a colon is appended to the filename before escaping.
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The colon is later used to separate the filename from the grep
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output so it is fine to add it here instead of a few lines later.
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The old code also wasn't POSIX compliant as it used \n in the
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replacement section of the s-command. Using \<newline> is the
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POSIX compatible method.
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LC_ALL=C was added to the two critical sed commands. POSIX sed
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manual recommends it when using sed to manipulate pathnames
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because in other locales invalid multibyte sequences might
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cause issues with some sed implementations. In case of GNU sed,
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these particular sed scripts wouldn't have such problems but some
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other scripts could have, see:
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info '(sed)Locale Considerations'
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This vulnerability was discovered by:
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cleemy desu wayo working with Trend Micro Zero Day Initiative
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Thanks to Jim Meyering and Paul Eggert discussing the different
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ways to fix this and for coordinating the patch release schedule
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with gzip.
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---
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src/scripts/xzgrep.in | 20 ++++++++++++--------
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1 file changed, 12 insertions(+), 8 deletions(-)
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diff --git a/src/scripts/xzgrep.in b/src/scripts/xzgrep.in
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index b180936..e5186ba 100644
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--- a/src/scripts/xzgrep.in
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+++ b/src/scripts/xzgrep.in
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@@ -180,22 +180,26 @@ for i; do
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{ test $# -eq 1 || test $no_filename -eq 1; }; then
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eval "$grep"
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else
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+ # Append a colon so that the last character will never be a newline
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+ # which would otherwise get lost in shell command substitution.
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+ i="$i:"
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+
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+ # Escape & \ | and newlines only if such characters are present
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+ # (speed optimization).
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case $i in
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(*'
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'* | *'&'* | *'\'* | *'|'*)
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- i=$(printf '%s\n' "$i" |
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- sed '
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- $!N
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- $s/[&\|]/\\&/g
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- $s/\n/\\n/g
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- ');;
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+ i=$(printf '%s\n' "$i" | LC_ALL=C sed 's/[&\|]/\\&/g; $!s/$/\\/');;
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esac
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- sed_script="s|^|$i:|"
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+
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+ # $i already ends with a colon so don't add it here.
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+ sed_script="s|^|$i|"
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# Fail if grep or sed fails.
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r=$(
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exec 4>&1
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- (eval "$grep" 4>&-; echo $? >&4) 3>&- | sed "$sed_script" >&3 4>&-
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+ (eval "$grep" 4>&-; echo $? >&4) 3>&- |
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+ LC_ALL=C sed "$sed_script" >&3 4>&-
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) || r=2
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exit $r
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fi >&3 5>&-
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--
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2.35.1
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