KSR[T] Advisory #011
Date: June 25, 1999
ID #: accelx-bo-011
Affected Program: Xi Graphics, Inc.'s Accelerated-X Server 4.x, 5.x
(and possibly earlier versions).
Author: Jordan Ritter <jpr5at_private>
Operating System(s): UNIX (Linux, FreeBSD, Solaris/x86, SCO)
Summary: Local users can gain administrative privileges by
exploiting multiple buffer overflows (stack
overwrites) in the Accelerated-X X server.
Problem Description: Accelerated-X Server is a commercial X server
available from http://www.xig.com/. By default,
the X server is installed setuid root so that
when it is executed by a user it still retains enough
privilege to load drivers, manipulate the
display, and log information.
However, due to insufficient bounds checking on
command-line parameters, an attacker can overflow
the X server by specifying a 48 byte display string,
or through a long string passed into the -query
command line parameter.
Compromise: Local users that can execute the Accelerated-X
Xserver can obtain root privileges.
Notes: We would like to thank Chris Evans for pointing
out the -query buffer overflow as well as additional
security holes relating to command line parameters.
Patch/Fix: For AccelX 5.x: XiG has made a patch available for
5.0.1 which corrects these and other potential
command line interface security holes. Users
running 5.0.0 have to apply the 5.0.1 patch prior
to applying the 5.0.2 patch. The patch is
available at ftp://ftp.xig.com/pub/updates.
For AccelX 4.x: Patch will be made available shortly.
An interim solution is to use an X server wrapper,
or to limit access to the Xaccel binary via a
special group.
The upcoming release of Maximum CDE 2.1 comes with
the 5.0.2 X Server, and is not vulnerable to these
attacks.
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