The Linux kernel had a root access exploit back in 2007, it was fixed, it came back and now it's fixed again.
"The vulnerability in a component of the operating system that translates values from 64 bits to 32 bits (and vice versa) was fixed once before in 2007 with the release of version 126.96.36.199," The Register's Dan Goodin reported. "But several months later, developers inadvertently rolled back the change, once again leaving the OS open to attacks that allow unprivileged users to gain full root access."This bug has been festering in the kernel for years. It's not network exploitable, a hacker needs a valid account on the machine before root access can be gained, but for many corporations and government agencies that use Linux - it's a big deal.