[jhgg]

Having a potentially untrusted client connect to the erlang node as a c_node (which seems to be what zerl does) is not a good idea generally, as connecting that way essentially allows the client to execute arbitrary code on the server.

[DuLR10]

Please correct me if I say anything wrong.

As far as I can tell, this is not possible at all; the serialization layer (Zerl) cannot send arbitrary code to another node. Now, assuming we implement this, I also think this is not possible due to how the server is designed; based on supervisors and child processes for user sessions.

We recently became aware that you can indeed send tuples that have fixed effects when using the supervisor behavior, so it may be totally possible and probable that one could exploit this vulnerability to some degree in our server. We plan to investigate more about it as we continue to learn more about OTP and the BEAM.

[toast0]

If you're using zerl on the client and plain dist on the server; the question isn't what Zerl can serialize, but what the server will process.

With stock OTP dist, there is no barrier between nodes. Stock OTP runs an rpc server that you can use to send function calls to run, which can include BEAM code to load (or file I/O to do); and even if that's disabled, you can spawn a process to run a function with arguments on a remote node without needing an rpc server at all.

[fluidwizard]

I think this behavior can be fixed by properly using something like `lib_chan`, but we needed something that worked first for our Func Prog Sweden demo.

Indeed a malicious client can craft an brutal kill message as long as it knows the PID a process (either a worker or a supervisor) for instance.