CVE-2026-41893: Signalk server Remote Code Execution Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-vmfm-ch9h-5c7g",
  "modified" : "2026-05-13T13:41:34Z",
  "published" : "2026-05-04T20:52:06Z",
  "aliases" : [ "CVE-2026-41893" ],
  "summary" : "Signal K Server's WebSocket Login Endpoint Lacks Rate Limiting (Credential Brute-Force)",
  "details" : "## Summary\n\nThe 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.\n\nAn 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).\n\n## Details\n\n**Vulnerable code:** `src/interfaces/ws.ts`, function `processLoginRequest` (lines 753-780)\n\nThe function directly calls `app.securityStrategy.login(msg.login.username, msg.login.password)` with no throttling or attempt tracking.\n\n**Rate-limited HTTP path for comparison:** `src/tokensecurity.ts` lines 609-617 apply `loginLimiter` middleware to the HTTP login routes at line 637.\n\n## Steps to Reproduce\n\n1. Start Signal K server with security enabled\n2. Open a WebSocket connection to `ws://server:3000/signalk/v1/stream?subscribe=none`\n3. Wait for the hello message\n4. Send login attempts in rapid succession:\n   ```json\n   {\"requestId\": \"1\", \"login\": {\"username\": \"admin\", \"password\": \"guess1\"}}\n   {\"requestId\": \"2\", \"login\": {\"username\": \"admin\", \"password\": \"guess2\"}}\n   ```\n5. Observe that all attempts are processed without any 429 response or throttling\n6. For comparison, send 100+ HTTP POST requests to `/signalk/v1/auth/login` — the 101st returns 429\n\nA POC script is available that demonstrates both the HTTP rate limiting working correctly and the WebSocket path accepting unlimited attempts.\n\n## Impact\n\n- Credential brute-forcing via the WebSocket protocol at ~20 attempts/sec (bcrypt-limited)\n- Complete bypass of the HTTP rate limiting defense\n- A single WebSocket connection is sufficient for unlimited attempts\n- With multiple parallel connections, throughput multiplies\n- A 10,000-word dictionary attack completes in ~8 minutes over a single connection\n\nSignal K servers are commonly deployed on boat networks where they may be accessible to other devices on the same LAN.\n\n## CWE\n\nCWE-307: Improper Restriction of Excessive Authentication Attempts\n\n## Suggested Fix\n\nTrack 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.\n\n## Context\n\nFound while building an open source maritime security scanner. Verified on v2.24.0 (current master).\n\nDiscovered by Mark Curphey",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "signalk-server"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.25.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 2.24.0"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/SignalK/signalk-server/security/advisories/GHSA-vmfm-ch9h-5c7g"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-41893"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/SignalK/signalk-server/pull/2568"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/SignalK/signalk-server/commit/215d81eb700d5419c3396a0fbf23f2e246dfac2d"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/SignalK/signalk-server"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/SignalK/signalk-server/releases/tag/v2.25.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-307" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-04T20:52:06Z",
    "nvd_published_at" : "2026-05-09T20:16:27Z"
  }
}