libpurple/protocols/irc/msgs.c in the IRC protocol plugin in libpurple in Pidgin before 2.6.2 allows remote IRC servers to cause a denial of service (NULL pointer dereference and application crash) via a TOPIC message that lacks a topic string.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A6435
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A11379
http://www.securityfocus.com/bid/36277
http://www.pidgin.im/news/security/index.php?id=40
http://secunia.com/advisories/36601
http://developer.pidgin.im/viewmtn/revision/info/ad2c6ee53ec9122b25aeb1f918db53be69bdeac3