Secunia Security Advisory – Ubuntu has issued an update for gdm. This fixes a vulnerability, which can be exploited by malicious, local users to bypass certain security restrictions.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/47144/sa20552.txt
Source: https://packetstormsecurity.com/files/47144/Secunia-Security-Advisory-20552.html