A sign extension issue was found in libFS, X.Org X11 libFS runtime library. The FSOpenServer() function did not check the sign of the returned data, leading to negative numbers being used in memory size calculations. This can result in allocating too little memory and then writing the returned data past the end of the buffer. When a X client is connected to a malcicious X server , (modified to return invalid values), it can cause arbirary code execution with the privileges of the user running the X client.
Public via: http://www.openwall.com/lists/oss-security/2013/05/23/3
Created libFS tracking bugs for this issue Affects: fedora-all [bug 966828]
libFS-1.0.4-6.20130524git26dc23446.fc18 has been pushed to the Fedora 18 stable repository. If problems still persist, please make note of it in this bug report.
This issue affects the version of libFS as shipped with Red Hat Enterprise Linux 5.
Statement: This issue affects the libFS package in Red Hat Enterprise Linux 5. Red Hat Product Security has rated this issue as having Moderate security impact. This issue is not planned to be fixed in Red Hat Enterprise Linux 5 as it is now in Production 3 Phase of the support and maintenance life cycle: https://access.redhat.com/support/policy/updates/errata/
libFS-1.0.5-1.fc19 has been pushed to the Fedora 19 stable repository. If problems still persist, please make note of it in this bug report.
External References: http://www.x.org/wiki/Development/Security/Advisory-2013-05-23