CVE-2026-35038: Signal K Server Information Disclosure

CVE-2026-35038 Overview

Signal K Server is a server application that runs on a central hub in a boat, providing marine data connectivity and integration. Prior to version 2.24.0, an arbitrary prototype read vulnerability exists via from field bypass. This vulnerability allows a low-privileged authenticated user to bypass prototype boundary filtering to extract internal functions and properties from the global prototype object, violating data isolation and allowing users to read more than they should.

Critical Impact

Authenticated attackers can bypass security boundaries to read sensitive internal prototype properties and functions, potentially exposing configuration data, authentication mechanisms, or other protected system information.

Affected Products

• Signal K Server versions prior to 2.24.0
• Marine vessel hub systems running vulnerable Signal K Server installations
• IoT maritime deployments utilizing Signal K for data aggregation

Discovery Timeline

• 2026-04-02 - CVE CVE-2026-35038 published to NVD
• 2026-04-02 - Last updated in NVD database

Technical Details for CVE-2026-35038

Vulnerability Analysis

This vulnerability is classified under CWE-20 (Improper Input Validation), where the application fails to properly validate or sanitize the from field parameter. The flaw enables authenticated users with low privileges to manipulate input in a way that bypasses prototype boundary filtering mechanisms. By exploiting this weakness, attackers can traverse beyond intended object boundaries and access the global prototype object, extracting internal functions and properties that should remain isolated.

The attack is network-accessible and requires only low-privilege authentication, making it relatively easy to exploit for any user with basic access to the Signal K Server. While the vulnerability does not allow modification or destruction of data, the confidentiality breach could expose sensitive system internals.

Root Cause

The root cause lies in insufficient input validation on the from field parameter. The application's prototype boundary filtering logic can be bypassed through specially crafted input values, allowing traversal to parent prototype objects. This occurs because the filtering mechanism does not adequately account for all possible bypass techniques when resolving object property chains.

Attack Vector

The attack is conducted over the network by an authenticated user with minimal privileges. The attacker crafts a malicious request containing a manipulated from field value designed to escape the normal prototype boundary restrictions. When processed by the server, this input bypasses the filtering logic and grants read access to properties and functions on the global prototype object.

The vulnerability mechanism involves manipulating the from field parameter to bypass prototype boundary filtering. The server's input validation fails to properly sanitize traversal sequences, allowing access to protected prototype properties. For detailed technical analysis and proof of concept, refer to the GitHub Security Advisory GHSA-qh3j-mrg8-f234.

Detection Methods for CVE-2026-35038

Indicators of Compromise

• Unusual API requests containing prototype traversal patterns in the from field parameter
• Access log entries showing attempts to read unexpected object properties or system internals
• Authentication logs showing low-privilege users accessing resources beyond their normal scope
• Error logs indicating prototype access violations or unexpected property resolution paths

Detection Strategies

• Implement request logging and analysis for API endpoints that process the from field parameter
• Deploy Web Application Firewall (WAF) rules to detect prototype pollution and traversal patterns
• Monitor for anomalous data access patterns from authenticated users, particularly access to system configuration or internal properties
• Enable verbose logging on Signal K Server to capture detailed request parameters

Monitoring Recommendations

• Configure alerts for requests containing suspicious prototype traversal sequences such as __proto__, constructor, or prototype
• Monitor server logs for unusual property access patterns or error messages related to prototype operations
• Implement rate limiting on API endpoints to slow down enumeration attempts
• Review access control logs regularly for privilege boundary violations

How to Mitigate CVE-2026-35038

Immediate Actions Required

• Upgrade Signal K Server to version 2.24.0 or later immediately
• Audit access logs for signs of prior exploitation attempts
• Review user accounts and ensure principle of least privilege is enforced
• Temporarily restrict network access to Signal K Server if immediate patching is not possible

Patch Information

The vulnerability has been patched in Signal K Server version 2.24.0. Users should upgrade to this version or later to remediate the vulnerability. The patch implements improved input validation and prototype boundary filtering to prevent the from field bypass attack.

Patch details are available in the GitHub Release v2.24.0 and the GitHub Security Advisory GHSA-qh3j-mrg8-f234.

Workarounds

• Restrict network access to Signal K Server to trusted networks and users only
• Implement additional authentication layers such as VPN or IP allowlisting for remote access
• Deploy a reverse proxy with request filtering to block suspicious prototype traversal patterns
• Monitor and audit all authenticated user activities until patching is complete

# Configuration example - Restrict network access via firewall
# Allow only trusted IP ranges to access Signal K Server
iptables -A INPUT -p tcp --dport 3000 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 3000 -j DROP