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Date: Fri, 16 Dec 2011 13:02:37 +0100 From: vladz <vladz@...zero.fr> To: full-disclosure@...ts.grok.org.uk Subject: X server wrapper permission bypass (CVE-2011-4613) Hi all, On Debian systems, the X wrapper (/usr/bin/X) is a setuid-root binary that checks for some security requirements before launching Xorg with root privileges. In its default configuration, it only allows users whose controlling TTY (console) to start the X server (see Xwrapper.config(5) for more informations). I recently found a way to bypass this permission[1] and so, it allows any user to start the X server. This is of course a minor security issue[2], but what is more critical is that the attack against CVE-2011-4029[3] (which allows any user to set the read permission on any arbitrary file thanks to a race condition in Xorg), can now be launched from a remote session and not even from a real TTY! I have updated the PoC[4] in consequence. And hope to get this "old" problem (CVE-2011-4029) fixed in Squeeze. [1] http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=652249 [2] http://security-tracker.debian.org/tracker/CVE-2011-4613 [3] http://security-tracker.debian.org/tracker/CVE-2011-4029 [4] http://vladz.devzero.fr/exploits/Xorg-CVE-2011-4029_inotify.c.txt Regards, -- http://vladz.devzero.fr PGP key 8F7E2D3C from pgp.mit.edu _______________________________________________ Full-Disclosure - We believe in it. Charter: http://lists.grok.org.uk/full-disclosure-charter.html Hosted and sponsored by Secunia - http://secunia.com/
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