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Response snapshot Oct 29, 2026, 02:31 UTC

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VulnerabilityCVE-2026-55235

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

In affected versions of langgraph-api (the LangGraph Server runtime), a run or cron could be created with a relative webhook target.

At a glance

Exploited
Not known
Severity
5.9 Medium (CVSS 3.1)
Chance of exploitation
0.4% in the next 30 days
Sources
1 source

What to do

GitHub lists first patched versions: langgraph-api: 0.10.0. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-2c9q-c2q9-qgqv (opens a new tab)

What happened

Summary

In affected versions of langgraph-api (the LangGraph Server runtime), a run or cron could be created with a relative webhook target. When the server later delivers such a webhook, it routes the request back into the same application through an in-process loopback transport that the authentication middleware treats as internal and does not authenticate.

As a result, a relative webhook target could reach the server's own routes that operate on threads and runs without the authentication context that applies to ordinary external requests.

In deployments that scope threads and runs by owner, this could allow a request associated with one user to reach routes operating on another user's thread, resulting in creation of a run on (or modification of the state of) a thread owned by another user, even where the corresponding direct external requests were correctly denied. Limited metadata from the targeted thread may be incorporated into the created run record.

Continue reading

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), - allow runs or crons to specify webhook targets, and - rely on per-user authorization to separate threads and runs between users.

Impact

- Integrity: creation of a run on, or modification of the state of, a thread owned by another user, beyond the requesting user's authorization scope. - Confidentiality: limited exposure of another user's thread metadata, incorporated into the created run record.

Patches / mitigation

The webhook URL policy now denies loopback delivery by default: the webhooks.url.disable_loopback policy defaults to enabled. This covers relative webhook targets routed through the in-process transport, as well as localhost-style hostnames, loopback address ranges, and hostnames that resolve into the loopback range.

Deployments that legitimately deliver webhooks to a route hosted on the same process can opt back in by setting webhooks.url.disable_loopback: false in langgraph.json (or the equivalent LANGGRAPH_WEBHOOKS configuration); do so only when you control the routes those webhooks reach, as they are delivered without authentication. Fixed in langgraph-api 0.10.0.

Operational guidance

- Upgrade to a release containing this change and keep loopback webhook delivery disabled unless required. - If loopback delivery is enabled, restrict it to routes you control and apply authorization within those routes.

Affected package ranges reported by GitHub: langgraph-api: < 0.10.0

Scores and how they were measured

CVSS base severity

5.9

Version 3.1As of

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

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

0.4%

Scored Percentile 30.2%

Model and measurement source (opens a new tab)

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-2c9q-c2q9-qgqv (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-2c9q-c2q9-qgqv, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  3. Primary source

    FIRST measured EPSS score (opens a new tab)

    Measured EPSS probability and percentile for CVE-2026-55235, scored 2026-10-28. This is a model estimate, not proof of exposure.

    Published Checked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 28). langgraph-api: Relative webhook targets in LangGraph Server can reach in-process routes without authentication (CVE-2026-55235). https://kevwire.com/record/CVE-2026-55235

MLA

"langgraph-api: Relative webhook targets in LangGraph Server can reach in-process routes without authentication (CVE-2026-55235)." KEVWire, 28 Oct. 2026, kevwire.com/record/CVE-2026-55235.

Chicago

KEVWire. "langgraph-api: Relative webhook targets in LangGraph Server can reach in-process routes without authentication (CVE-2026-55235)." Last modified October 28, 2026. https://kevwire.com/record/CVE-2026-55235.

Evidence summary (plain text)

langgraph-api: Relative webhook targets in LangGraph Server can reach in-process routes without authentication (Aug 19, 2026).
In affected versions of langgraph-api (the LangGraph Server runtime), a run or cron could be created with a relative webhook target. When the server later delivers such a webhook, it routes the request back into the same application through an in-process loopback transport that the authentication middleware treats as internal and does not authenticate. As a result, a relative webhook target could reach the server's own routes that operate on threads and runs without the authentication context that applies to ordinary external requests.
CVSS 5.9 (version 3.1; evidence as of Oct 28, 2026; https://github.com/advisories/GHSA-2c9q-c2q9-qgqv).
EPSS 0.4% for the following 30 days, scored Oct 28, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-55235&date=2026-10-28).
Sources:
GitHub-reviewed advisory GHSA-2c9q-c2q9-qgqv: https://github.com/advisories/GHSA-2c9q-c2q9-qgqv
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
FIRST measured EPSS score: https://api.first.org/data/v1/epss?cve=CVE-2026-55235&date=2026-10-28
Record ID: CVE-2026-55235.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 29, 2026, 02:16 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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