Nortel Multimedia Communication Server (MSC) 5100 3.0.13 does not verify credentials during call placement, which allows remote attackers to spoof and redirect VoIP calls, possibly related to the snoop command.
https://exchange.xforce.ibmcloud.com/vulnerabilities/45752
http://www.vupen.com/english/advisories/2008/2779
http://www.securityfocus.com/bid/31640
http://voipshield.com/research-details.php?id=119
http://support.nortel.com/go/main.jsp?cscat=BLTNDETAIL&id=775223