CVE-2026-55235 PUBLISHED

langgraph-api: Relative webhook targets in LangGraph Server can reach in-process routes without authentication

Assigner: GitHub_M
Reserved: 16.06.2026 Published: 14.09.2026 Updated: 14.09.2026

langgraph-api implements the LangGraph API for rapid development and testing. Prior to 0.10.0, langgraph-api permits a run or cron to specify a relative webhook target that is delivered through an in-process loopback transport, and the authentication middleware treats that transport as internal without applying the authentication context used for external requests. In deployments that rely on per-user authorization to separate threads and runs, an authenticated user can direct a webhook to the server's own thread and run routes, allowing creation of a run on or modification of another user's thread and limited incorporation of the targeted thread's metadata into the created run record. The affected path requires webhook targets and per-user authorization boundaries; deployments that deliberately re-enable loopback delivery should restrict it to controlled same-process routes because those webhooks remain unauthenticated. This issue is fixed in version 0.10.0.

Metrics

CVSS Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:L
CVSS Score: 5.9

Product Status

Vendor langchain-ai
Product langgraph-api
Versions
  • Version < 0.10.0 is affected

References

Problem Types

  • CWE-287: Improper Authentication CWE