The msn_slp_sip_recv function in libpurple/protocols/msn/slp.c in the MSN protocol plugin in libpurple in Pidgin before 2.6.2 allows remote attackers to cause a denial of service (NULL pointer dereference and application crash) via an SLP invite message that lacks certain required fields, as demonstrated by a malformed message from a KMess client.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A6322
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A11852
http://www.securityfocus.com/bid/36277
http://www.pidgin.im/news/security/index.php?id=39
http://secunia.com/advisories/36601
http://developer.pidgin.im/viewmtn/revision/info/b4a95ea62b81a06ffc1993912471c511b786efdd