Vulnerability · Published Sep 14, 2026 · Assigned by GitHub_M
CVE-2026-55235langgraph-api: Relative webhook targets in LangGraph Server can reach in-process routes without authentication
Medium 5.9
In plain English
A medium-severity improper authentication in langgraph-api from langchain-ai. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 30% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| PyPI | langgraph-api | 0.10.0 | GHSA-2c9q-c2q9-qgqv |
| PyPI | langgraph-api | 0.10.0 | PYSEC-2026-3857 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| langchain-ai | langgraph-api | < 0.10.0 |
Weakness: CWE-287 · Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:L