CVE-2025-69203: Signal K Server Auth Bypass Vulnerability

CVE-2025-69203 Overview

CVE-2025-69203 is a social engineering vulnerability in Signal K Server, a server application designed to run on a central hub in boats for marine data management. This vulnerability combines multiple security weaknesses in the access request system that enable attackers to craft convincing social engineering attacks against administrators.

The vulnerability chain involves permission obfuscation in the admin UI, IP address spoofing via untrusted X-Forwarded-For headers, and information disclosure that allows device enumeration. When exploited together, these flaws allow attackers to impersonate legitimate devices, request elevated admin permissions while displaying misleading descriptions suggesting readonly access, and spoof trusted internal IP addresses to increase the likelihood of administrator approval.

Critical Impact

Attackers can gain administrative access to Signal K Server through social engineering by crafting deceptive access requests that appear to originate from trusted internal devices, potentially compromising the entire marine data management system.

Affected Products

• Signal K Server versions prior to 2.19.0
• Signal K Server 2.19.0-beta1
• Signal K Server 2.19.0-beta2
• Signal K Server 2.19.0-beta3
• Signal K Server 2.19.0-beta4

Discovery Timeline

• 2026-01-01 - CVE-2025-69203 published to NVD
• 2026-01-06 - Last updated in NVD database

Technical Details for CVE-2025-69203

Vulnerability Analysis

This vulnerability exploits weaknesses in the Signal K Server access request system that allows devices to request access to the server. The attack surface involves three interrelated flaws that can be chained together for maximum impact.

First, when a device creates an access request, it specifies three fields: clientId, description, and permissions. The SignalK admin UI displays the description field prominently to administrators when showing pending requests, but the actual permissions field (which determines the access level granted) is less visible or displayed separately. This UI design flaw enables permission obfuscation attacks.

Second, the access request handler unconditionally trusts the X-Forwarded-For HTTP header to determine the client's IP address. While this header is intended to preserve original client IPs when requests pass through reverse proxies, the lack of validation allows attackers to spoof their source IP address. The spoofed IP is then displayed to administrators in the access request approval interface.

Third, an information disclosure vulnerability allows enumeration of device and source names, enabling attackers to identify legitimate devices on the network and impersonate them.

Root Cause

The root cause is classified under CWE-290 (Authentication Bypass by Spoofing). The vulnerability stems from multiple design decisions that prioritize convenience over security:

1. Insufficient UI Transparency: The admin interface fails to prominently display the actual permissions being requested alongside the device description, allowing malicious descriptions to mask elevated permission requests.

2. Unconditional Header Trust: The server trusts the X-Forwarded-For header without any validation or configuration options to restrict which proxies can set this header.

3. Information Exposure: The ability to enumerate device names provides attackers with reconnaissance data needed to craft convincing impersonation attacks.

Attack Vector

The attack is network-based and requires user interaction (administrator approval). An attacker can execute this attack by:

1. Enumerating existing device names using the information disclosure vulnerability
2. Crafting an access request that impersonates a known legitimate device
3. Setting the description field to suggest readonly or limited access
4. Setting the permissions field to request admin level access
5. Spoofing the X-Forwarded-For header to display a trusted internal IP address
6. Waiting for an administrator to approve the deceptively presented request

The attack does not require prior authentication and can be executed remotely over the network. The vulnerability mechanism involves HTTP header manipulation and UI-based social engineering. Attackers submit crafted access requests with misleading description fields and spoofed IP addresses via the X-Forwarded-For header. The admin interface displays this deceptive information, leading administrators to unknowingly grant elevated permissions. For complete technical details, refer to the GitHub Security Advisory.

Detection Methods for CVE-2025-69203

Indicators of Compromise

• Access requests with admin or elevated permissions paired with descriptions suggesting limited or readonly access
• Multiple access requests originating from IP addresses that do not match expected network topology
• Access requests claiming to originate from internal IP ranges (192.168.x.x, 10.x.x.x, 172.16-31.x.x) when received from external interfaces
• New administrator accounts or elevated permissions granted to previously unknown devices

Detection Strategies

• Implement logging of all access request submissions including the full request payload, actual source IP, and X-Forwarded-For header values
• Configure web application firewalls to flag requests where X-Forwarded-For contains private IP ranges when received from public interfaces
• Create alerts for access requests where the permissions field contains elevated privileges like admin or readwrite
• Monitor for patterns of access request submissions from the same source attempting different device impersonations

Monitoring Recommendations

• Enable comprehensive audit logging for the Signal K Server access request approval workflow
• Implement network monitoring to detect external requests claiming internal IP origins
• Review administrator approval patterns and establish baseline behavior for anomaly detection
• Configure SIEM rules to correlate access request approvals with subsequent privilege usage

How to Mitigate CVE-2025-69203

Immediate Actions Required

• Upgrade Signal K Server to version 2.19.0 or later immediately
• Review all recently approved access requests for suspicious permission grants
• Audit current device permissions and revoke any unauthorized admin access
• Implement network-level controls to validate X-Forwarded-For headers before they reach the application

Patch Information

SignalK has released version 2.19.0 which addresses this vulnerability. The fix is available via the GitHub Release v2.19.0. Users should upgrade immediately to ensure protection against this social engineering attack vector.

Additional details about the vulnerability and remediation are available in the GitHub Security Advisory GHSA-vfrf-vcj7-wvr8.

Workarounds

• Configure a reverse proxy in front of Signal K Server to strip or validate X-Forwarded-For headers from untrusted sources
• Implement network segmentation to restrict access request submissions to trusted internal networks only
• Establish administrative policies requiring secondary verification (out-of-band confirmation) before approving any access requests
• Temporarily disable the access request feature if not required for operations until the patch can be applied

# Example: Nginx configuration to strip X-Forwarded-For from untrusted sources
# Add to your reverse proxy configuration

# Only trust X-Forwarded-For from known proxy addresses
set_real_ip_from 10.0.0.0/8;
set_real_ip_from 172.16.0.0/12;
set_real_ip_from 192.168.0.0/16;
real_ip_header X-Forwarded-For;
real_ip_recursive on;

# Strip X-Forwarded-For header for direct connections
proxy_set_header X-Forwarded-For $remote_addr;