Cisco has updated its security advisory on the recent issue on some affected version of Cisco IOS can be crashed by certain crafted SIP packets destined to port 5060. The issue is compounded by a related bug which allows traffic to TCP 5060 and UDP port 5060 on devices not configured for SIP.

Cisco reported that there are data streams that could appear to be unintentionally triggering the vulnerability as well.

http://www.cisco.com/warp/public/707/cisco-sa-20070131-sip.shtml.