Insecurity outfit VSR Security has warned that the Linux operating system contains a serious security flaw that can be exploited to gain superuser rights on a target system.
The vulnerability, in the Linux implementation of the Reliable Datagram Sockets (RDS) protocol, affects unpatched versions of the Linux kernel, starting from 2.6.30, where the RDS protocol was first included. VSR Security said that Linux installations are only vulnerable if the CONFIG_RDS kernel configuration option is set, and if there are no restrictions on unprivileged users loading packet family modules, as is the case on most stock distributions.
Kernel functions responsible for copying data between kernel and user space. If they don't verify that a user-provided address resided in the user segment, a local attacker could issue specially crafted socket function calls to write arbritrary values into kernel memory. Once they have done that it is a doddle to escalate privileges to root.
The outfit has been showing off a proof-of-concept exploit to demonstrate the severity of the vulnerability. The exploit was tested on Ubuntu 10.04 (64-bit) and opened a root shell. There is a patch available and the problem will be fixed in the next Kernel upgrade.