Nortel UNIStim protocol, as used in Communication Server 1000 and other products, uses predictable sequence numbers, which allows remote attackers to hijack sessions via sniffing or brute force attacks.
osvdb.org/44379
secunia.com/advisories/29747
support.nortel.com/go/main.jsp?cscat=BLTNDETAIL&id=713455
www.securityfocus.com/bid/28691
www.securitytracker.com/id?1019847
www.voipshield.com/research-details.php?id=27&s=4&threats_details=&threats_category=0&threats_vendor=0&limit=20&sort=discovered&sortby=DESC
exchange.xforce.ibmcloud.com/vulnerabilities/41801