From SecurityFocus BID15536: "

Bugtraq ID: 15536
Class: Design Error
CVE: CVE-2005-3272
Remote: Yes
Local: No

Linux Kernel is susceptible to an information disclosure vulnerability in its network bridging functionality.
This issue allows attackers to poison the bridge forwarding table, causing packets to be incorrectly forwarded to the wrong interface. Information gained from the packets may aid the malicious user in further attacks. Kernel versions 2.6.11.11 and prior are vulnerable to this issue.

Solution: Kernel version 2.6.11.12 is available to address this issue.
Ubuntu has released advisory USN-219-1 to address various issues affecting the Linux kernel. Please see the referenced advisory for more information.".