The find prototype in scripting/engine_v8.h in MongoDB 2.4.0 through 2.4.4 allows remote authenticated users to cause a denial of service (uninitialized pointer dereference and server crash) or possibly execute arbitrary code via an invalid RefDB object.
MongoDB before 2.0.9 and 2.2.x before 2.2.4 does not properly validate requests to the nativeHelper function in SpiderMonkey, which allows remote authenticated users to cause a denial of service (invalid memory access and server crash) or execute arbitrary code via a crafted memory address in the first argument.
bson/_cbsonmodule.c in the mongo-python-driver (aka. pymongo) before 2.5.2, as used in MongoDB, allows context-dependent attackers to cause a denial of service (NULL pointer dereference and crash) via vectors related to decoding of an "invalid DBRef."
MongoDB 2.4.x before 2.4.5 and 2.5.x before 2.5.1 allows remote authenticated users to obtain internal system privileges by leveraging a username of __system in an arbitrary database.