Local DoS and possible privilege escalation via routing sockets

What FreeBSD says

The rtsock_msg_buffer() function serializes routing information into a buffer. As a part of this, it copies sockaddr structures into a sockaddr_storage structure on the stack. It assumes that the source sockaddr length field had already been validated, but this is not necessarily the case, and it's possible for a malicious userspace program to craft a request which triggers a 127-byte overflow. In practice, this overflow immediately overwrites the canary for the rtsock_msg_buffer() stack frame, resulting in a panic once the function returns.

Impact

The bug allows an unprivileged user to crash the kernel by triggering a stack buffer overflow in rtsock_msg_buffer(). In particular, the overflow will corrupt a stack canary value that is verified when the function returns; this mitigates the impact of the stack overflow by triggering a kernel panic. Other kernel bugs may exist which allow userspace to find the canary value and thus defeat the mitigation, at which point local privilege escalation may be possible.

Excerpt from the FreeBSD advisory. Read the original for the full text and the fix.