n8n: Prior to versions 1.123.32, 2.17.4, and 2.18.1, the MCP OAuth client registration endpoint…
n8n
- Severity
- High, CVSS 7.5
- CVSS vector
- CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Record
- CVE-2026-42236
- Affects
- n8n
- Known exploited
- Not listed in the CISA Known Exploited Vulnerabilities catalog
- Published
- Record first published by the source
- May 4, 2026
- Source last modified
- June 17, 2026
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.
Description quoted from the NVD record.
Who is affected
n8n is an open source tool that lets you automate tasks by connecting apps and services. This flaw affects versions of n8n older than the fixed releases 1.123.32, 2.17.4 and 2.18.1. It is in the part of n8n that lets AI assistants sign up to connect to it (the MCP connection feature). Anyone who can reach your n8n system over the network, without logging in, could send very large sign-up requests that use up the server's memory and make n8n stop working. Turning off MCP access in n8n's settings does not block this, because the sign-up part stays reachable either way. This flaw is rated High.
What to do
- Find out who installed or runs n8n for your organization: a staff member, a volunteer, or an IT provider or vendor.
- If someone in your organization runs it, have them check which version is installed and update to
1.123.32,2.17.4or2.18.1, whichever matches the release line you use. - If an IT provider or vendor runs n8n for you, send them this advisory and ask when the update will be done.
- Do not count on switching off MCP access as protection, because this flaw can be reached whether that setting is on or off. Update instead.
Analysis written from the source record as of June 17, 2026 and reviewed before publishing.