The 2.4 and 2.6 kernels contain a vulnerability in the iso9660 (CDROM) filesystem which can be used by a local attacker to obtain root privileges. The exploit requires creating a specially-crafted filesystem and getting the kernel to mount it. Many systems are configured to automatically mount CDs on insertion, however, so the possibility of this vulnerability being exploited by users with physical access to the system is real. The 2.4.26 kernel contains the fix, which will also be merged into the upcoming 2.6.6 release.
Source : http://lwn.net/Articles/80480/