A libx11 security update has been released for Debian 6 LTS

Package : libx11
Version : 2:1.3.3-4+squeeze2
CVE ID : CVE-2013-7439

Abhishek Arya discovered a buffer overflow in the MakeBigReq macro
provided by libx11, which could result in denial of service or the
execution of arbitrary code.

Several other xorg packages (e.g. libxrender) will be recompiled against
the fixed package after the release of this update. For detailed
information on the status of recompiled packages please refer to the
Debian Security Tracker at
https://security-tracker.debian.org/tracker/CVE-2013-7439

For the oldstable distribution (squeeze), this problem has been fixed
in version 2:1.3.3-4+squeeze2.

For the stable distribution (wheezy), this problem has been fixed in
version 2:1.5.0-1+deb7u2.

  Libx11 security update for Debian 6 LTS