There is a NULL pointer dereference flaw in the Linux kernel that can be exploited by attackers to gain root access to a vulnerable machine. The vulnerability is in version 2.6.21 of the kernel and some Linux vendors already have taken steps to fix the vulnerability. Red Hat has released a fix for the flaw in several versions of its Linux distributions. There have not been any public exploits released for the vulnerability, which was identified in mid-October and so far, no public exploits have been released.
Source: https://threatpost.com/critical-flaw-found-linux-kernel-110509/73037/