CVE-2026-25228: Signal K Server Path Traversal Flaw

CVE-2026-25228 Overview

CVE-2026-25228 is a path traversal vulnerability in Signal K Server, a server application that runs on a central hub in boats for marine data aggregation. The vulnerability exists in the applicationData API and allows authenticated users on Windows systems to read, write, and list arbitrary files and directories on the filesystem. The root cause is insufficient input validation in the validateAppId() function, which blocks forward slashes (/) but not backslashes (\), enabling attackers to escape the intended applicationData directory.

Critical Impact

Authenticated attackers can read sensitive configuration files, write malicious content to arbitrary locations, and enumerate the file system on Windows-based Signal K Server deployments.

Affected Products

• Signal K Server versions prior to 2.20.3
• Windows-based Signal K Server deployments
• Marine navigation systems using Signal K Server

Discovery Timeline

• 2026-02-02 - CVE CVE-2026-25228 published to NVD
• 2026-02-03 - Last updated in NVD database

Technical Details for CVE-2026-25228

Vulnerability Analysis

This path traversal vulnerability (CWE-22) affects the applicationData API endpoint in Signal K Server. The core issue lies in how the application handles directory separator characters across different operating systems. While the validateAppId() function properly sanitizes forward slashes (/) to prevent path traversal attacks, it fails to account for the Windows-specific backslash (\) character, which the path.join() function on Windows interprets as a valid directory separator.

When an authenticated user submits a malicious application ID containing backslash sequences (such as ..\..\..\), the server processes these as legitimate directory traversal commands on Windows systems, allowing the attacker to break out of the intended applicationData directory sandbox.

Root Cause

The vulnerability stems from incomplete input validation in the validateAppId() function. The function was designed with Unix-like systems in mind, where the forward slash is the standard directory separator. However, on Windows systems, both forward slashes and backslashes are valid directory separators. The path.join() function in Node.js on Windows normalizes these paths and treats backslashes as directory separators, effectively bypassing the forward-slash-only validation check.

Attack Vector

The attack requires network access and authentication to the Signal K Server. An attacker with valid credentials can exploit this vulnerability by sending specially crafted requests to the applicationData API endpoint. By including backslash-based directory traversal sequences in the application ID parameter, the attacker can:

1. Read arbitrary files - Access sensitive configuration files, credentials, or system information
2. Write arbitrary files - Create or modify files outside the intended directory, potentially enabling further exploitation
3. List directory contents - Enumerate the filesystem to discover sensitive files and directory structures

The vulnerability is particularly concerning in marine environments where Signal K Servers may contain navigation data, vessel information, and network configurations.

Detection Methods for CVE-2026-25228

Indicators of Compromise

• Unusual API requests to the applicationData endpoint containing backslash characters (\) or encoded backslash sequences (%5C)
• Access attempts to files outside the normal applicationData directory structure
• Unexpected file reads or writes in system directories on Windows-based Signal K Server hosts
• Authentication logs showing API calls with suspicious path patterns from authenticated users

Detection Strategies

• Monitor HTTP request logs for the applicationData API endpoint for requests containing backslash sequences or path traversal patterns
• Implement file integrity monitoring on Windows servers running Signal K Server to detect unauthorized file access or modifications
• Deploy web application firewall (WAF) rules to detect and block path traversal attempts targeting the API
• Enable verbose logging for the Signal K Server application to capture all API requests and responses

Monitoring Recommendations

• Establish baseline activity patterns for the applicationData API and alert on anomalous request patterns
• Configure SIEM rules to correlate authentication events with subsequent suspicious API activity
• Monitor for file access events outside the normal Signal K Server data directories on Windows hosts
• Review access logs regularly for any requests containing encoded or unencoded backslash characters

How to Mitigate CVE-2026-25228

Immediate Actions Required

• Upgrade Signal K Server to version 2.20.3 or later immediately
• Audit existing Signal K Server deployments to identify any Windows-based installations running vulnerable versions
• Review access logs for signs of exploitation, particularly API requests containing backslash characters
• Restrict network access to the Signal K Server to trusted users and networks until patching is complete

Patch Information

The vulnerability has been fixed in Signal K Server version 2.20.3. The patch addresses the input validation issue by properly sanitizing both forward slashes and backslashes in the validateAppId() function. Users should update to this version or later to remediate the vulnerability.

For detailed information about the fix, see the GitHub Security Advisory and the commit implementing the fix.

Workarounds

• Restrict access to the Signal K Server to trusted networks only using firewall rules or network segmentation
• Implement additional authentication requirements or access controls for the applicationData API endpoint
• Deploy a reverse proxy or WAF in front of the Signal K Server configured to block requests containing backslash sequences
• If feasible, run Signal K Server on Linux-based systems which are not affected by this specific vulnerability

# Configuration example
# Restrict network access to Signal K Server using iptables (Linux) or Windows Firewall
# Example: Allow only trusted IP ranges to access Signal K Server port (default 3000)
iptables -A INPUT -p tcp --dport 3000 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 3000 -j DROP