The CmdAuthenticate::authenticateX509 function in db/commands/authenticationcommands.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.
MongoDB before 2.4.13 and 2.6.x before 2.6.8 allows remote attackers to cause a denial of service via a crafted UTF-8 string in a BSON request.