CVE-2026-55235
langgraph-api: Relative webhook targets in LangGraph Server can reach in-process routes without authentication
Impact
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
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| pip | langgraph-api | < 0.10.0 | 0.10.0 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/advisories/GHSA-2c9q-c2q9-qgqv
- https://github.com/langchain-ai/helm/security/advisories/GHSA-2c9q-c2q9-qgqv
- https://nvd.nist.gov/vuln/detail/CVE-2026-55235
- https://github.com/langchain-ai/docs/blob/7b70fbacab21f84d9c6f9848f86cdeb471adbb50/src/langsmith/agent-server-changelog.mdx
- https://github.com/pypa/advisory-database/tree/main/vulns/langgraph-api/PYSEC-2026-3857.yaml