xzgrep-ZDI-CAN-16587.patch (3488B)
1 From 69d1b3fc29677af8ade8dc15dba83f0589cb63d6 Mon Sep 17 00:00:00 2001 2 From: Lasse Collin <lasse.collin@tukaani.org> 3 Date: Tue, 29 Mar 2022 19:19:12 +0300 4 Subject: [PATCH] xzgrep: Fix escaping of malicious filenames (ZDI-CAN-16587). 5 6 Malicious filenames can make xzgrep to write to arbitrary files 7 or (with a GNU sed extension) lead to arbitrary code execution. 8 9 xzgrep from XZ Utils versions up to and including 5.2.5 are 10 affected. 5.3.1alpha and 5.3.2alpha are affected as well. 11 This patch works for all of them. 12 13 This bug was inherited from gzip's zgrep. gzip 1.12 includes 14 a fix for zgrep. 15 16 The issue with the old sed script is that with multiple newlines, 17 the N-command will read the second line of input, then the 18 s-commands will be skipped because it's not the end of the 19 file yet, then a new sed cycle starts and the pattern space 20 is printed and emptied. So only the last line or two get escaped. 21 22 One way to fix this would be to read all lines into the pattern 23 space first. However, the included fix is even simpler: All lines 24 except the last line get a backslash appended at the end. To ensure 25 that shell command substitution doesn't eat a possible trailing 26 newline, a colon is appended to the filename before escaping. 27 The colon is later used to separate the filename from the grep 28 output so it is fine to add it here instead of a few lines later. 29 30 The old code also wasn't POSIX compliant as it used \n in the 31 replacement section of the s-command. Using \<newline> is the 32 POSIX compatible method. 33 34 LC_ALL=C was added to the two critical sed commands. POSIX sed 35 manual recommends it when using sed to manipulate pathnames 36 because in other locales invalid multibyte sequences might 37 cause issues with some sed implementations. In case of GNU sed, 38 these particular sed scripts wouldn't have such problems but some 39 other scripts could have, see: 40 41 info '(sed)Locale Considerations' 42 43 This vulnerability was discovered by: 44 cleemy desu wayo working with Trend Micro Zero Day Initiative 45 46 Thanks to Jim Meyering and Paul Eggert discussing the different 47 ways to fix this and for coordinating the patch release schedule 48 with gzip. 49 --- 50 src/scripts/xzgrep.in | 20 ++++++++++++-------- 51 1 file changed, 12 insertions(+), 8 deletions(-) 52 53 diff --git a/src/scripts/xzgrep.in b/src/scripts/xzgrep.in 54 index b180936..e5186ba 100644 55 --- a/src/scripts/xzgrep.in 56 +++ b/src/scripts/xzgrep.in 57 @@ -180,22 +180,26 @@ for i; do 58 { test $# -eq 1 || test $no_filename -eq 1; }; then 59 eval "$grep" 60 else 61 + # Append a colon so that the last character will never be a newline 62 + # which would otherwise get lost in shell command substitution. 63 + i="$i:" 64 + 65 + # Escape & \ | and newlines only if such characters are present 66 + # (speed optimization). 67 case $i in 68 (*' 69 '* | *'&'* | *'\'* | *'|'*) 70 - i=$(printf '%s\n' "$i" | 71 - sed ' 72 - $!N 73 - $s/[&\|]/\\&/g 74 - $s/\n/\\n/g 75 - ');; 76 + i=$(printf '%s\n' "$i" | LC_ALL=C sed 's/[&\|]/\\&/g; $!s/$/\\/');; 77 esac 78 - sed_script="s|^|$i:|" 79 + 80 + # $i already ends with a colon so don't add it here. 81 + sed_script="s|^|$i|" 82 83 # Fail if grep or sed fails. 84 r=$( 85 exec 4>&1 86 - (eval "$grep" 4>&-; echo $? >&4) 3>&- | sed "$sed_script" >&3 4>&- 87 + (eval "$grep" 4>&-; echo $? >&4) 3>&- | 88 + LC_ALL=C sed "$sed_script" >&3 4>&- 89 ) || r=2 90 exit $r 91 fi >&3 5>&- 92 -- 93 2.35.1 94