The onReadyRead function in core/coreauthhandler.cpp in Quassel before 0.12.4 allows remote attackers to cause a denial of service (NULL pointer dereference and crash) via invalid handshake data.
https://github.com/quassel/quassel/commit/e678873
http://www.openwall.com/lists/oss-security/2016/04/30/4
http://www.openwall.com/lists/oss-security/2016/04/30/2
http://quassel-irc.org/node/129
http://lists.opensuse.org/opensuse-updates/2016-05/msg00063.html
http://lists.fedoraproject.org/pipermail/package-announce/2016-May/183746.html
http://lists.fedoraproject.org/pipermail/package-announce/2016-May/183585.html
http://lists.fedoraproject.org/pipermail/package-announce/2016-May/183571.html