Asterisk crashes when handed an otherwise valid request message but with no URI and no SIP-version in the request-line of the message. Asterisk versions 1.2.15 and 1.4.0, along with prior versions, are affected.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/54963/MU-200703-01.txt
Source: https://packetstormsecurity.com/files/54963/MU-Security-Advisory-2007-03.01.html