GitHub Security Advisory: GHSA-7gcj-phff-2884
Package: signalk-server (NPM)
Severity: HIGH (CVSS 7.5)
CWE: CWE-400: Uncontrolled Resource Consumption, CWE-1333: Inefficient Regular Expression Complexity
Vulnerable versions: < 2.25.0
Patched in: 2.25.0

Summary: Signal K Server has an Unauthenticated Regular Expression Denial of Service (ReDoS) via WebSocket Subscription Paths

Details:
## Summary
The SignalK server is vulnerable to an unauthenticated Regular Expression Denial of Service (ReDoS) attack within its WebSocket subscription handling logic. By injecting unescaped regex metacharacters into the `context` parameter of a stream subscription, an attacker can force the server's Node.js event loop into a catastrophic backtracking loop when evaluating long string identifiers (like the server's self UUID). This results in a total Denial of Service (DoS) where the server CPU spikes to 100% and becomes completely unresponsive to further API or socket requests.

## Description
The vulnerability stems from flawed string-to-regex conversion in `signalk-server/src/subscriptionmanager.ts`. The `contextMatcher()` and `pathMatcher()` functions convert wildcard strings (e.g., `*`) into regular expressions to match incoming data against client subscriptions.

While the code attempts to escape `.` and `*` characters, it fails to escape other dangerous regular expression metacharacters—such as `+`, `(`, `)`, `?`, `[`, and `]`. Because of this, an attacker can submit a crafted `context` that contains nested quantifiers (e.g., `([a-z0-9:-]+)+!`). When the server attempts to test this malicious regex against legitimate, lengthy data identifiers (like `vessels.urn:mrn:signalk:uuid:d384dc156010`), the regex engine fails to find a match at the end of the string but initiates billions of catastrophic backtracking operations trying to resolve the nested combinations. Since Node.js runs on a single-threaded event loop, this locks up the thread indefinitely.

## Affected Code Blocks & Files
**File:** `signalk-server/src/subscriptionmanager.ts`

**Affected lines for Context subscriptions (282-300):**
```typescript
function contextMatcher(...) {
  if (subscribeCommand.context) {
    if (isString(subscribeCommand.context)) {
      const pattern = subscribeCommand.context
        .replace(/\./g, '\\.')
        .replace(/\*/g, '.*')
      const matcher = new RegExp('^' + pattern + '$') // VULNERABILITY: User input compiled into regex directly
      return (normalizedDeltaData: WithContext) =>
        matcher.test(normalizedDeltaData.context) ||
```

**Affected lines for Path subscriptions (276-280):**
```typescript
function pathMatcher(path: string = '*') {
  const pattern = path.replace(/\./g, '\\.').replace(/\*/g, '.*')
  const matcher = new RegExp('^' + pattern + '$') // VULNERABILITY: Same issue here
  return (aPath: string) => matcher.test(aPath)
}
```

## Proof of Concept (PoC) Steps

```
const WebSocket = require('ws');
const http = require('http');

const HOST = 'localhost';
const PORT = 3000;
const WS_URL = `ws://${HOST}:${PORT}/signalk/v1/stream?subscribe=none`;
// Use the API endpoint to measure real server processing lag (requires JSON serialization)
const HTTP_URL = `http://${HOST}:${PORT}/signalk/v1/api/`;

console.log(`[+] Target Server API: ${HTTP_URL}`);
console.log(`[+] Target WebSocket: ${WS_URL}`);

let requestCount = 0;

// Polling f