CVE-2026-42236 — n8n
CVE-2026-42236 is a CWE-770 vulnerability in n8n. A fix is available for n8n — see the affected versions and patch details below.
n8n: Unauthenticated Denial of Service via MCP Client Registration
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-42236.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
n8nnpmDescription
Impact
The MCP OAuth client registration endpoint accepted unauthenticated requests and stored client data without adequate resource controls. An unauthenticated remote attacker could exhaust server memory resources by sending large registration payloads, rendering the n8n instance unavailable. The MCP enable/disable toggle gates MCP access but did not restrict client registrations, meaning the endpoint is reachable regardless of whether MCP access is enabled on the instance.
The patches address the unbound registration with an upper bound of registered clients and disabling creation when MCP is disabled on the instance. Mean to restrict the payload size of requests already exist and can be used to control additional risks.
Patches
The issue has been fixed in n8n versions 1.123.32, 2.17.4, and 2.18.1. Users should upgrade to one of these versions or later to remediate the vulnerability.
Workarounds
If upgrading is not immediately possible, administrators should consider the following temporary mitigations:
- Restrict network access to the n8n instance to prevent requests from untrusted sources.
- Reduce the maximum accepted payload size by lowering the
N8N_PAYLOAD_SIZE_MAXenvironment variable from its default value.
These workarounds do not fully remediate the risk and should only be used as short-term mitigation measures.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | n8n | all versions | 1.123.32npm install n8n@1.123.32 |
| 📦npm | n8n | ≥ 2.18.0&&< 2.18.1 | 2.18.1npm install n8n@2.18.1 |
| 📦npm | n8n | ≥ 2.0.0&&< 2.17.4 | 2.17.4npm install n8n@2.17.4 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for n8n, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update n8n to 1.123.32 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-42236 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 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-42236 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-42236. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-42236 in your dependencies?
O3 Security finds CVE-2026-42236 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.