How severe is CVE-2026-55235?

CVE-2026-55235 has a CVSS score of 5.9/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2026-55235?

CVE-2026-55235 affects the following packages: langgraph-api (PyPI). Ecosystems affected: PyPI.

How do I fix CVE-2026-55235?

Update langgraph-api to 0.10.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-55235 is resolved across your whole dependency graph.

How do I detect CVE-2026-55235 in my PyPI dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for langgraph-api. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.

How do I mitigate CVE-2026-55235 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

How does O3 Security protect against CVE-2026-55235?

O3 pinpoints whether CVE-2026-55235 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Is CVE-2026-55235 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-55235 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

When was CVE-2026-55235 published, and has it been updated?

CVE-2026-55235 was published on August 19, 2026 and was last updated on August 19, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐍

🐍 PyPI

Not in CISA KEV

MEDIUM severity

CVE-2026-55235

MEDIUM

CVE-2026-55235 is a medium-severity (CVSS 5.9) vulnerability in langgraph-api. O3 Security confirms whether CVE-2026-55235 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.

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

Published

Aug 19, 2026

Updated

Aug 19, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Aug 19, 2026 · OSV.dev, FIRST.org (EPSS)

Real-World Exposure

1 pkg affected

🐍langgraph-api

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

Description

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.

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 Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐍PyPI	`langgraph-api`	all versions	0.10.0

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for langgraph-api. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update langgraph-api to 0.10.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-55235 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-55235 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Tailored to CVE-2026-55235. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

## 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

O3 Security · Impact-Aware SCA

Is CVE-2026-55235 in your dependencies?

O3 detects CVE-2026-55235 across PyPI dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

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