CVE-2026-46339: 9router: Unauthenticated Remote Code Execution via unprotected MCP custom plugin routes

9router exposes two unauthenticated API endpoints that, when chained together, allow any network-adjacent attacker to execute arbitrary OS commands as the user running the 9router process — with zero prerequisites and no credentials required.

The vulnerability exists because the Next.js middleware that enforces authentication (src/proxy.js) only guards 8 explicitly listed routes. The attack surface of /api/cli-tools/* and /api/mcp/* (40+ routes) receives no authentication whatsoever.