n8n before 1.123.89, 2.x before 2.45.5, 2.46.x before 2.46.1, and 3.x before 3.0.1 contains an open redirect vulnerability in the unauthenticated MCP OAuth dynamic client registration flow, which accepts arbitrary redirect_uri values via the /mcp-oauth/register endpoint. Attackers can send victims crafted /mcp-oauth/authorize URLs that redirect them to attacker-controlled sites before instance checks run, enabling phishing.