There exists a use after free vulnerability in Reverb. Reverb supports the VARIANT datatype, which is supposed to represent an arbitrary object in C++. When a tensor proto of type VARIANT is unpacked, memory is first allocated to store the entire tensor, and a ctor is called on each instance. Afterwards, Reverb copies the content in tensor_content to the previously mentioned pre-allocated memory, which results in the bytes in tensor_content overwriting the vtable pointers of all the objects which were previously allocated. Reverb exposes 2 relevant gRPC endpoints: InsertStream and SampleStream. The attacker can insert this stream into the server’s database, then when the client next calls SampleStream they will unpack the tensor into RAM, and when any method on that object is called (including its destructor) the attacker gains control of the Program Counter. We recommend upgrading past git commit https://github.com/google-deepmind/reverb/commit/6a0dcf4c9e842b7f999912f792aaa6f6bd261a25
The product deserializes untrusted data without sufficiently verifying that the resulting data will be valid.
It is often convenient to serialize objects for communication or to save them for later use. However, deserialized data or code can often be modified without using the provided accessor functions if it does not use cryptography to protect itself. Furthermore, any cryptography would still be client-side security – which is a dangerous security assumption. Data that is untrusted can not be trusted to be well-formed. When developers place no restrictions on “gadget chains,” or series of instances and method invocations that can self-execute during the deserialization process (i.e., before the object is returned to the caller), it is sometimes possible for attackers to leverage them to perform unauthorized actions, like generating a shell.