CVE-2026-48775: LangGraph Checkpoint: Unsafe JSON deserialization in checkpoint loading

LangGraph’s JsonPlusSerializer can reconstruct Python objects from JSON checkpoint payloads. Under conditions where someone could modify checkpoint bytes at rest in the backing store, the deserialization path could reconstruct objects beyond what the application expects, which could in turn result in code execution at checkpoint load time.

This is a defense-in-depth issue. The affected behavior is reachable only when checkpoint bytes at rest in the backing store can be modified by an unauthorized party. In most deployments that prerequisite already implies a serious incident; the additional concern is turning “checkpoint-store write access” into code execution in the application runtime.

There is no evidence of this behavior being triggered in the wild, and the team is not aware of a practical path to it in existing deployments today. This change is intended to reduce the surface available after a checkpoint-store incident.