n8n: Open Redirect via MCP OAuth Dynamic Client Registration

Impact

The MCP OAuth registration and authorization endpoints are enabled by default and require no authentication. Any caller could register an OAuth client with an arbitrary redirect_uri, and a crafted authorization URL then redirected the visitor to that URI before the instance's checks ran, turning the n8n instance into an open redirector. No tokens or session data were included in the redirect. A victim had to open the crafted URL.

Patches

The issue has been fixed in n8n versions 1.123.89, 2.45.5, 2.46.1 and 3.0.1. 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 n8n instance access to fully trusted users only.
• Apply network-level controls or a reverse-proxy rule to block unauthenticated access to the /mcp-oauth/register and /mcp-oauth/authorize endpoints.
• Educate users not to follow unsolicited links pointing to your n8n instance's OAuth endpoints.

These workarounds do not fully remediate the risk and should only be used as short-term mitigation measures.