Signal K Server's WebSocket Login Endpoint Lacks Rate Limiting (Credential Brute-Force)

Summary

The HTTP login endpoints (POST /login and POST /signalk/v1/auth/login) are protected by express-rate-limit (default: 100 attempts per 10-minute window, configurable via HTTP_RATE_LIMITS). The WebSocket login path — sending {login: {username, password}} messages over an established WebSocket connection — calls app.securityStrategy.login() directly without any rate limiting.

An attacker can bypass HTTP rate limiting entirely by opening a WebSocket connection and attempting unlimited password guesses at the speed bcrypt allows (~20 attempts/sec with 10 salt rounds).

Details

Vulnerable code: src/interfaces/ws.ts, function processLoginRequest (lines 753-780)

The function directly calls app.securityStrategy.login(msg.login.username, msg.login.password) with no throttling or attempt tracking.

Rate-limited HTTP path for comparison: src/tokensecurity.ts lines 609-617 apply loginLimiter middleware to the HTTP login routes at line 637.

Steps to Reproduce

1. Start Signal K server with security enabled
2. Open a WebSocket connection to ws://server:3000/signalk/v1/stream?subscribe=none
3. Wait for the hello message
4. Send login attempts in rapid succession:

   {"requestId": "1", "login": {"username": "admin", "password": "guess1"}}
   {"requestId": "2", "login": {"username": "admin", "password": "guess2"}}
   

5. Observe that all attempts are processed without any 429 response or throttling
6. For comparison, send 100+ HTTP POST requests to /signalk/v1/auth/login — the 101st returns 429

A POC script is available that demonstrates both the HTTP rate limiting working correctly and the WebSocket path accepting unlimited attempts.

Impact

• Credential brute-forcing via the WebSocket protocol at ~20 attempts/sec (bcrypt-limited)
• Complete bypass of the HTTP rate limiting defense
• A single WebSocket connection is sufficient for unlimited attempts
• With multiple parallel connections, throughput multiplies
• A 10,000-word dictionary attack completes in ~8 minutes over a single connection

Signal K servers are commonly deployed on boat networks where they may be accessible to other devices on the same LAN.

CWE

CWE-307: Improper Restriction of Excessive Authentication Attempts