Summary

Prior to langgraph-checkpoint version 3.0 , LangGraph’s JsonPlusSerializer (used as the default serialization protocol for all checkpointing) contains a remote code execution (RCE) vulnerability when deserializing payloads saved in the "json" serialization mode.

If an attacker can cause your application to persist a payload serialized in this mode, they may be able to also send malicious content that executes arbitrary Python code during deserialization.

Upgrading to version langgraph-checkpoint 3.0 patches this vulnerability by preventing deserialization of custom objects saved in this mode.

If you are deploying in langgraph-api, any version 0.5 or later is also free of this vulnerability.

Details

Affected file / component

jsonplus.py

By default, the serializer attempts to use "msgpack" for serialization. However, prior to version 3.0 of the checkpointer library, if illegal Unicode surrogate values caused serialization to fail, it would fall back to using the "json" mode.

When operating in this mode, the deserializer supports a constructor-style format (lc == 2, type == "constructor") for custom objects to allow them to be reconstructed at load time. If an attacker is able to trigger this mode with a malicious payload, deserializing allow the attacker to execute arbitrary functions upon load.

Who is affected

This issue affects all users of langgraph-checkpoint versions earlier than 3.0 who:

1. Allow untrusted or user-supplied data to be persisted into checkpoints, and
2. Use the default serializer (or explicitly instantiate JsonPlusSerializer) that may fall back to "json" mode.

If your application only processes trusted data or does not allow untrusted checkpoint writes, the practical risk is reduced.

Proof of Concept (PoC)

from...