A vulnerability exists in the SIP channel driver (channels/chan_sip.c) in all versions of Asterisk prior to 1.2.13. Local and remote attackers are able to cause a denial of service (resource consumption) via unspecified vectors that result in the creation of “a real pvt structure” that uses more resources than necessary.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/51625/asterisk-bugtraq.asc
Source: https://packetstormsecurity.com/files/51625/asterisk-bugtraq.asc.html