GHSA-vmfm-ch9h-5c7g
Signal K Server's WebSocket Login Endpoint Lacks Rate Limiting (Credential Brute-Force)
Packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| npm | signalk-server | < 2.25.0 | 2.25.0 |
Details
As written in the advisory (Markdown source, shown as plain text).
## 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:
```json
{"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
## Suggested Fix
Track failed login attempts per remote IP in a shared store (or reuse the existing express-rate-limit store) that is checked in both the HTTP login middleware and the processLoginRequest WebSocket handler.
## Context
Found while building an open source maritime security scanner. Verified on v2.24.0 (current master).
Discovered by Mark Curphey
References
External links from the advisory. They lead to third-party sites.
- https://github.com/SignalK/signalk-server/security/advisories/GHSA-vmfm-ch9h-5c7g
- https://nvd.nist.gov/vuln/detail/CVE-2026-41893
- https://github.com/SignalK/signalk-server/pull/2568
- https://github.com/SignalK/signalk-server/commit/215d81eb700d5419c3396a0fbf23f2e246dfac2d
- https://github.com/SignalK/signalk-server
- https://github.com/SignalK/signalk-server/releases/tag/v2.25.0