Signal K Server Vulnerable to Unauthenticated Information Disclosure via Exposed Endpoints

[Note] This is a separate issue from the RCE vulnerability (State Pollution) currently being patched. While related to tokensecurity.js, it involves different endpoints and risks.

Summary

An unauthenticated information disclosure vulnerability allows any user to retrieve sensitive system information, including the full SignalK data schema, connected serial devices, and installed analyzer tools. This exposure facilitates reconnaissance for further attacks.

Details

The vulnerability stems from the fact that several sensitive API endpoints are not included in the authentication middleware's protection list in src/tokensecurity.js.

Vulnerable Code Analysis:

1. Missing Protection: The tokensecurity.js file defines an array of paths that require authentication. However, the following paths defined in src/serverroutes.ts are missing from this list:

   • /skServer/serialports
   • /skServer/availablePaths
   • /skServer/hasAnalyzer

2. Unrestricted Access: Because they are missing from the protection list, the http_authorize middleware allows access to these paths even when enableSecurity is set to true.

Exploit Scenario:

1. Reconnaissance: An attacker scans the server for these endpoints.
2. Data Extraction:
   • Querying /skServer/availablePaths returns the full JSON schema of the vessel's data (e.g., environment.sun.sunrise, navigation.position), allowing the attacker to know exactly what data points are available for targeting.
   • Querying /skServer/serialports reveals connected hardware (e.g., /dev/ttyUSB0), aiding in physical device targeting.

PoC

The following Python script demonstrates the vulnerability by querying the exposed endpoints without any authentication headers.

import urllib.request
import json

BASE_URL = "http://localhost:3000"

def check_endpoint(name, path):
    url = f"{BASE_URL}{path}"
    print(f"[*] Checking {name} at {url}...")
    try:
        req = urllib.request.Request(url)
        with urllib.request.urlopen(req) as response:
            if response.getcode() == 200:
                print(f"[!] VULNERABLE: {name} is accessible without authentication!")
                content = response.read().decode('utf-8')
                print(f"    Snippet: {content[:100]}...")
            else:
                print(f"[-] Secure: {response.getcode()}")
    except urllib.error.HTTPError as e:
        print(f"[-] Secure: {e.code}")
    except Exception as e:
        print(f"[-] Error: {e}")

if __name__ == "__main__":
    print("--- SignalK Information Disclosure PoC ---")
    check_endpoint("Serial Ports", "/skServer/serialports")
    check_endpoint("Available Paths", "/skServer/availablePaths")
    check_endpoint("Analyzer Check", "/skServer/hasAnalyzer")

Expected Result: The script will output [!] VULNERABLE for all three endpoints, showing snippets of the leaked JSON data.

Impact

Verified Information Disclosure: During our verification, we successfully retrieved the following sensitive information without any authentication:

1. Full Data Schema: The /skServer/availablePaths endpoint returned the complete JSON schema of the vessel's data.
   • Example: environment.sun.sunrise, navigation.position
   • Leakage of Internal State: We also observed entries like notifications.security.accessRequest.readwrite.attacker-device-32, which revealed the presence and IDs of pending access requests (traces of our DoS attack), showing that internal server state is exposed.
2. Hardware Configuration: The /skServer/serialports endpoint exposed the list of connected serial devices.
3. System Capabilities: The /skServer/hasAnalyzer endpoint revealed whether traffic analysis tools were installed.

This information allows an attacker to map the system's internal state and capabilities, significantly facilitating further targeted attacks (Reconnaissance).

Remediation

Update src/tokensecurity.js Add the missing paths to the list of protected routes in src/tokensecurity.js.

// src/tokensecurity.js

// ... existing protected paths ...
;[
  '/apps',
  '/appstore',
  '/plugins',
  '/restart',
  '/runDiscovery',
  '/security',
  '/vessel',
  '/providers',
  '/settings',
  '/webapps',
  '/skServer/inputTest',
  // ADD THESE LINES:
  '/skServer/serialports',
  '/skServer/availablePaths',
  '/skServer/hasAnalyzer'
].forEach((p) =>
  app.use(`${SERVERROUTESPREFIX}${p}`, http_authorize(false))
)