Ubuntu Security Notice 403-1 – The DBE and Render extensions in X.org were vulnerable to integer overflows, which could lead to memory overwrites. An authenticated user could make a specially crafted request and execute arbitrary code with root privileges.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/53569/USN-403-1.txt
Source: https://packetstormsecurity.com/files/53569/Ubuntu-Security-Notice-403-1.html