A buffer overflow flaw has been found in the X.org composite extension. The
upstream bug has more details:
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:
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.
XID val = IncludeInferiors;
@@ -492,6 +493,7 @@
w, h, 0, 0);
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
- 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:
Red Hat Enterprise Linux 5 and current versions of Fedora were not affected as
described in comment #2.