PYSEC-2026-3858

Summary

In affected versions of langgraph-api (the LangGraph Server runtime), the run-creation path authorized the assistant attached to a run using a different authorization event than the rest of the assistant-handling code paths. Direct assistant reads and cron creation dispatch the assistants.read authorization event; run creation dispatched assistants.search with an incomplete value. In deployments whose custom authorization handlers register only an assistants.read handler (without an assistants.search handler and without a global fallback handler), no handler was consulted on the run-creation path, the returned filter set was empty, and the owner constraint was omitted from the resulting query.

As a result, in those deployments a request to create a run could reference a private assistant owned by another user, even where direct assistant reads, assistant search, and cron creation against that assistant were correctly denied. The run-creation response merged the referenced assistant's metadata, config, and context into fields returned to the requesting user. These fields can carry sensitive configuration; the runtime encrypts them at rest for that reason.

We have no evidence of this behavior occurring in the wild.

Affected users / systems

You may be affected if you:

• run langgraph-api (the LangGraph Server / Agent Server runtime, including via the LangGraph Platform Helm chart), and
• use custom authorization handlers that gate assistant access through an assistants.read or assistants.search handler rather than a global handler covering all assistant events.

Deployments without custom authorization handlers, or whose handlers apply an equivalent owner filter across all assistant events (for example through a global handler), are not affected.

Impact

• Confidentiality: exposure of another user's private assistant metadata, config, and context through the run-creation response. These fields can contain sensitive configuration.
• Integrity: creation of a run associated with another user's private assistant, beyond the requesting user's authorization scope; the run is then carried out using that assistant's configuration.

Patches / mitigation

Run creation, and the parallel cron-creation path, now dispatch the assistants.read authorization event in both the in-memory and gRPC/Postgres runtimes, matching direct assistant reads. Client-supplied run and cron metadata is no longer forwarded into that authorization event, so handlers receive a consistent value shape and determine access by returning an owner filter that is applied server-side. Fixed in langgraph-api 0.10.0.

This is a behavioral change for deployments with custom authorization handlers:

• Handlers that gated assistant access only through assistants.search during run creation are no longer consulted on that path; provide an equivalent assistants.read handler that returns the same owner filter.
• The metadata field on the assistants.read event during run and cron creation is no longer populated; handlers that read or stamped it should move that logic into the run/cron create handlers.

Operational guidance

• Register an assistants.read handler (or a global handler covering it) that returns an owner-style filter, and confirm parity across the assistant read, search, and run/cron creation paths.
• Upgrade to a release containing this change.