CVE-2026-41893

EPSS 0.04%

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

Published: 5/4/2026Modified: 5/13/2026
Also known as:GHSA-vmfm-ch9h-5c7g

Description

## 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

Affected packages (1)

CVSS scores

SourceVersionSeverityVector
osvCVSS 4.0—CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N

References (6)