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94 lines
3.4 KiB
94 lines
3.4 KiB
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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