Vulnerability · Published May 4, 2026 · Assigned by GitHub_M
CVE-2026-42236n8n: Unauthenticated Denial of Service via MCP Client Registration
High 8.7
In plain English
A high-severity resource allocation without limits in n8n from n8n-io. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 42% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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 packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| npm | n8n | 1.123.32 | GHSA-49m9-pgww-9vq6 |
| npm | n8n | 2.18.1 | GHSA-49m9-pgww-9vq6 |
| npm | n8n | 2.17.4 | GHSA-49m9-pgww-9vq6 |
Affected products (as reported)
Weakness: CWE-770 · Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
References
- https://github.com/n8n-io/n8n/security/advisories/GHSA-49m9-pgww-9vq6 x_refsource_CONFIRM