The SIP module in Ingate Firewall before 4.6.1 and SIParator before 4.6.1 does not reuse SIP media ports in unspecified call hold and send-only stream scenarios, which allows remote attackers to cause a denial of service (port exhaustion) via unspecified vectors.
http://www.vupen.com/english/advisories/2008/0108
http://www.securitytracker.com/id?1019177
http://www.securitytracker.com/id?1019176
http://www.securityfocus.com/bid/27222
http://www.ingate.com/relnote-461.php