IRC Services before 5.0.62, and 5.1 before 5.1pre3, allows remote attackers to disconnect users with guest nicknames by linking a guest nickname to a nickname that is already registered.
https://exchange.xforce.ibmcloud.com/vulnerabilities/34946
http://www.vupen.com/english/advisories/2007/2440
http://www.ircservices.za.net/Changes.txt
http://www.ircservices.za.net/
http://lists.ircservices.za.net/pipermail/ircservices/2007/005307.html
http://lists.ircservices.za.net/pipermail/ircservices/2007/005306.html
http://lists.ircservices.za.net/pipermail/ircservices/2007/005299.html