JWT Authentication Bypass

const jwt = require("jsonwebtoken");

function getUser(req) {
  const token = req.headers.authorization.split(" ")[1];

  // Vulnerable: decode only reads the payload, it never checks the signature
  const claims = jwt.decode(token);

  return { id: claims.sub, role: claims.role };
}

// Almost as bad - no algorithm allowlist, so alg can be swapped:
// const claims = jwt.verify(token, publicKey);

const jwt = require("jsonwebtoken");

const VERIFY_OPTIONS = {
  algorithms: ["RS256"],                 // pinned, so alg in the header is ignored
  issuer: "https://auth.example.com/",
  audience: "api://reports",
  maxAge: "15m",
  clockTolerance: 5,
};

function getUser(req) {
  const header = req.headers.authorization || "";
  if (!header.startsWith("Bearer ")) {
    throw new AuthError("Missing bearer token");
  }

  const claims = jwt.verify(header.slice(7), publicKey, VERIFY_OPTIONS);

  if (revocationList.has(claims.jti)) {
    throw new AuthError("Token revoked");
  }

  return { id: claims.sub, role: claims.role };
}