ctcphandler.cpp in Quassel before 0.6.3 and 0.7.x before 0.7.1 allows remote attackers to cause a denial of service (unresponsive IRC) via multiple Client-To-Client Protocol (CTCP) requests in a PRIVMSG message.
http://ubuntu.com/usn/usn-991-1
http://security.gentoo.org/glsa/glsa-201311-03.xml
http://secunia.com/advisories/55581
http://quassel-irc.org/node/115