CVE-2026-42235 is a cross-site scripting flaw in n8n, scored CVSS 9.6 (critical) in the record. A crafted MCP OAuth client name could run script in a user's authenticated session. Upgrade to n8n 1.123.32, 2.17.4 or 2.18.1, and restrict access to the MCP OAuth registration endpoint.
What's affected
The NVD record lists n8n versions before 1.123.32, 2.17.4 and 2.18.1 as affected, with those three as the fixed versions. The advisory text itself says the fix landed in 2.14.2 and later, so any release at or above your line's fixed version in the record is the safe target.
The attack needs an unauthenticated party to register a client, a user to approve the consent dialog, a second user to revoke that access, and someone to click a link in the resulting notice.
How to check if you're exposed
- Read your n8n version.
n8n --version
- Check whether MCP server functionality is enabled on your instance, and whether the MCP OAuth registration endpoint is reachable from untrusted networks.
- Review the list of authorized MCP clients and remove any you do not recognize.
What to do now
- Upgrade to 1.123.32, 2.17.4 or 2.18.1, matching your release line.
- Until then, restrict access to the instance and the MCP OAuth registration endpoint to trusted users, as the advisory suggests.
- Turn MCP server functionality off if you do not use it.
- Treat n8n credentials as sensitive, and rotate any you suspect were exposed.
Why it matters
The classes are CWE-79, cross-site scripting, and CWE-87, improper neutralization of alternate XSS syntax. The client name was shown in a toast notification without being made safe, so script in the name could run in the victim's browser. The advisory says that could lead to credential and session token theft, workflow changes or privilege escalation.
The n8n advisory rates it high at 8.8, while the NVD record scores 9.6. The difference is mostly how the scope change is counted. The KEV flag is false, and I found no report of exploitation in the wild.
Quick check
Which version should I trust, 2.14.2 or 2.17.4?
The advisory text mentions 2.14.2, while the NVD record names 1.123.32, 2.17.4 and 2.18.1. Upgrading to the latest in your line satisfies both, and you can confirm in the n8n release notes.
Sources
Last reviewed: 19 October 2026.
