langgraph-api implements the LangGraph API for rapid development and testing. From 0.1.2 until 0.15.0, JavaScript or TypeScript custom authentication Store authorization handlers can return a rewritten namespace that is not carried across the runtime boundary and applied before the Store operation. An authenticated user can therefore access another user's Store namespace when a deployment relies on namespace rewriting for isolation, allowing unauthorized reads, overwrites, searches, or deletions. Python custom authentication and handlers that reject unauthorized namespaces instead of rewriting them are not affected. This issue is fixed in version 0.15.0.

Affected: PyPI: langgraph-api

## Summary

LangGraph deployments using JavaScript or TypeScript custom authentication may fail to apply Store authorization changes returned by an authorization handler. In affected deployments, an authenticated user may be able to access Store data outside their authorized namespace.

## Required conditions

A deployment is affected only when all of the following conditions apply:

- It uses an affected `langgraph-api` version. - It runs JavaScript or TypeScript custom authentication. - Its Store authorization handler relies on rewriting the requested namespace to restrict each user to their own data. - The attacker can authenticate as an ordinary user. - Multiple users' data is stored through the affected authorization path.

Python custom authentication handlers are not affected. JavaScript or TypeScript handlers that reject unauthorized namespace requests instead of rewriting them are also not affected.

The attack does not require administrator privileges, user interaction, a race condition, or the bypass of another mitigation.

## Impact

An authenticated user may be able to read, overwrite, search, or delete Store data belonging to another user.

## Patches

The issue is fixed in `langgraph-api` version `0.15.0`. The server now carries changes made by a JavaScript or TypeScript authorization handler across the runtime boundary and applies them before performing the Store operation. It validates the resulting namespace after authorization and rejects the request if an…