What’s Vulnerable › Vulnerabilities
CVE-2026-42236: n8n: Unauthenticated Denial of Service via MCP Client Registration
- Severity: high (CVSS 7.5 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 0.5% probability of exploitation in the next 30 days
- Public exploit or detection template: none known
- Published: 2026-05-04 · updated 2026-06-17
- Weakness: CWE-770
Description
n8n is an open source workflow automation platform. Prior to versions 1.123.32, 2.17.4, and 2.18.1, 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. This issue has been patched in versions 1.123.32, 2.17.4, and 2.18.1.
Affected products
- n8n-io n8n: before 1.123.32; from 2.17.0 through 2.17.4; 2.18.0 — fixed in 1.123.32
How to fix
Upgrade to a fixed version: n8n-io n8n 1.123.32. Check the vendor advisory for mitigations.
References
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