Executive brief
n8n is a workflow automation platform used to connect and orchestrate business processes across multiple applications. An unauthenticated attacker can register arbitrary redirect URLs and craft a phishing link that silently redirects users to an external site when they deny an OAuth consent prompt, potentially leading to credential theft or malware distribution.
Technical details
The vulnerability is an open redirect (CWE-601) in the `/mcp-oauth/register` endpoint, which accepts OAuth client registrations without authentication and allows arbitrary `redirect_uri` values. The `handleDeny` handler in the OAuth consent flow does not validate the registered redirect URI before redirecting users, enabling an attacker to redirect victims to attacker-controlled URLs. The attack requires user interaction (clicking "Deny" on the consent page) but no authentication or privileges. The issue has been patched in n8n versions 1.123.32, 2.17.4, and 2.18.1.
Affected products
- n8n n8n before 1.123.32, 2.0.0 before 2.17.4, 2.18.0 before 2.18.1
Timeline
- 2026-04-29: disclosed
- 2026-04-29: patched: Patches released in versions 1.123.32, 2.17.4, and 2.18.1