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bc82eb79 AB |
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 |