The CtcpParser::packedReply method in core/ctcpparser.cpp in Quassel before 0.7.3 allows remote attackers to cause a denial of service (crash) via a crafted Client-To-Client Protocol (CTCP) request, as demonstrated in the wild in September 2011.
https://exchange.xforce.ibmcloud.com/vulnerabilities/69682
https://bugs.gentoo.org/show_bug.cgi?id=382313
http://www.ubuntu.com/usn/USN-1200-1
http://www.securityfocus.com/bid/49526
http://www.openwall.com/lists/oss-security/2011/09/09/7
http://www.openwall.com/lists/oss-security/2011/09/08/7