An assertion failure was found in BIND, which checks the validity of messages containing TSIG resource records. This flaw allows an attacker that knows or successfully guesses the name of the TSIG key used by the server to use a specially-crafted message, potentially causing a BIND server to reach an inconsistent state or cause a denial of service. A majority of BIND servers have an internally-generated TSIG session key whose name is trivially guessable, and that key exposes the vulnerability unless specifically disabled.