[$] The TCP SACK panic

Selective
acknowledgment (SACK) is a technique used by TCP to help alleviate
congestion
that can arise due to the retransmission of dropped packets. It allows
the endpoints to describe which pieces of the data they have received,
so that only the missing pieces need to be retransmitted. However, a bug
was recently found in the Linux implementation of SACK that allows remote
attackers to panic the system by sending crafted SACK information.