CVE-2026-55236: langchain-ai langgraph-api Improper Authorization

Vulnerability summary

CVE-2026-55236 is a medium (CVSS 5.9) Improper Authorization vulnerability in langchain-ai langgraph-api. EPSS estimates a 0.26% chance of exploitation in the next 30 days, higher than 16% of scored vulnerabilities.

Timeline

1. 14-09-2026
   PublishedVulnerability first disclosed.
2. 14-09-2026
   Last modifiedVulnerability information updated.

Description

langgraph-api implements the LangGraph API for rapid development and testing. Prior to 0.10.0, the langgraph-api run-creation path authorizes the assistant attached to a run by dispatching assistants.search with an incomplete value instead of the assistants.read event used by direct reads and cron creation. In deployments with custom resource handlers that register only assistants.read, omit an assistants.search handler, and have no global fallback handler, no applicable handler supplies an owner filter, allowing a low-privileged user to reference another user's private assistant through POST /runs or POST /threads/{thread_id}/runs. The run-creation response can disclose the private assistant's metadata, config, and context, and the run can execute using that assistant's configuration. Deployments without custom authorization handlers, or with an equivalent owner filter applied through a global handler or across all assistant events, are not affected. This issue is fixed in version 0.10.0.

• CWE-285Improper AuthorizationThe product does not perform or incorrectly performs an authorization check when an actor attempts to access a resource or perform an action.