The CmdAuthenticate::_authenticateX509 function in db/commands/authentication_commands.cpp in mongod in MongoDB 2.6.x before 2.6.2 allows remote attackers to cause a denial of service (daemon crash) by attempting authentication with an invalid X.509 client certificate.
https://jira.mongodb.org/browse/SERVER-13753
https://github.com/mongodb/mongo/commit/c151e0660b9736fe66b224f1129a16871165251b