A buffer overflow flaw has been found in the X.org composite extension. The upstream bug has more details: http://bugs.freedesktop.org/show_bug.cgi?id=7447 By running a server at depth 16, it becomes possible for a local user to overflow a buffer by creating a window with depth 32, then resizing it.
FC6, F7, Fdevel, and rhels 5.0.z, 5.1 are not vulnerable because of this patch: localhost:~/vertigo/rpms/xorg-x11-server/RHEL-5% cat xorg-x11-server-1.1.0-dont-backfill-bg-none.patch Disable backfilling of windows created with bg=none, which otherwise would force a framebuffer readback. --- ./composite/compalloc.c.spiffiffity 2006-03-13 16:59:55.000000000 -0500 +++ ./composite/compalloc.c 2006-04-12 16:37:50.000000000 -0400 @@ -478,6 +478,7 @@ * Copy bits from the parent into the new pixmap so that it will * have "reasonable" contents in case for background None areas. */ +#if 0 if (pGC) { XID val = IncludeInferiors; @@ -492,6 +493,7 @@ w, h, 0, 0); FreeScratchGC (pGC); } +#endif return pPixmap; }
We are changing the severity here to moderate. Here is some additional information provided by Adam Jackson: - the Composite extension is not enabled by default in RHEL4, so the user would have had to go out of their way to turn it on. - we don't ship any compositing manager in RHEL4, so they'd need to have installed one. - the exploit requires the ability to authenticate to the X server, so the attacker would need to have already gained rights equivalent to the user.
For Red Hat Enterprise Linux 4, this issue was addressed in RHSA-2007:0898: https://rhn.redhat.com/errata/RHSA-2007-0898.html Red Hat Enterprise Linux 5 and current versions of Fedora were not affected as described in comment #2.