CVE-2026-23515: Signal K Server RCE Vulnerability

CVE-2026-23515 Overview

CVE-2026-23515 is a critical command injection vulnerability in Signal K Server, a server application that runs on a central hub in boats for marine data management. Prior to version 1.5.0, authenticated users with write permissions can execute arbitrary shell commands on the Signal K server when the set-system-time plugin is enabled. This vulnerability is particularly dangerous because unauthenticated users can also exploit it if security is disabled on the Signal K server.

The vulnerability occurs due to unsafe construction of shell commands when processing navigation.datetime values received via WebSocket delta messages. This allows attackers to inject malicious commands through specially crafted datetime values.

Critical Impact

Remote attackers can achieve full system compromise through arbitrary command execution on vulnerable Signal K Server installations, potentially gaining complete control over the marine navigation hub and connected systems.

Affected Products

• Signal K Server versions prior to 1.5.0
• Signal K set-system-time plugin (when enabled)
• Marine navigation systems running vulnerable Signal K Server installations

Discovery Timeline

• 2026-02-02 - CVE-2026-23515 published to NVD
• 2026-02-03 - Last updated in NVD database

Technical Details for CVE-2026-23515

Vulnerability Analysis

This command injection vulnerability (CWE-78) allows attackers to execute arbitrary shell commands on the underlying operating system. The vulnerability exists in the set-system-time plugin's handling of datetime values received through WebSocket delta messages. When the server receives a navigation.datetime value, it constructs a shell command without proper input validation, allowing attackers to break out of the intended command context and execute arbitrary commands.

The vulnerability is network-accessible and requires low privileges to exploit for authenticated users. However, when security is disabled on the Signal K server (a common configuration in local marine networks), the vulnerability can be exploited without any authentication, significantly increasing its severity and potential impact.

Root Cause

The root cause is the lack of input validation and sanitization of the datetime parameter before it is interpolated into shell commands. The set-system-time plugin directly passes user-supplied datetime values to shell execution functions without verifying that the input conforms to expected datetime formats, enabling command injection through specially crafted payloads.

Attack Vector

Attackers can exploit this vulnerability by sending malicious WebSocket delta messages containing crafted navigation.datetime values. The attack can be executed remotely over the network. For authenticated attacks, write permissions are required. For unauthenticated exploitation, the target Signal K server must have security disabled.

The attack flow involves:

1. Establishing a WebSocket connection to the Signal K server
2. Sending a delta message with a malicious navigation.datetime value
3. The server passes the unsanitized value to a shell command
4. Attacker-controlled commands execute with server privileges

           console.error("Set-system-time supports only linux-like os's")
         } else {
           if( ! plugin.useNetworkTime(options) ){
+            // Validate datetime format to prevent command injection
+            if (!/^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}(\.\d+)?Z?$/.test(datetime)) {
+              lastMessage = 'Invalid datetime format received: ' + String(datetime).substring(0, 50)
+              logError(lastMessage)
+              return
+            }
             const useSudoFallback = typeof options.sudo === 'undefined' || options.sudo
             // Convert ISO 8601 datetime to format compatible with both GNU date and BusyBox date
             // e.g., "2024-01-10T17:55:03.000Z" → "2024-01-10 17:55:03"

Source: GitHub Commit Update

Detection Methods for CVE-2026-23515

Indicators of Compromise

• Unusual WebSocket connections to the Signal K server with malformed datetime values
• Unexpected process spawning from the Signal K server process
• Shell command execution patterns containing injection characters (;, |, &&, backticks) in datetime fields
• Anomalous network connections originating from the Signal K server host

Detection Strategies

• Monitor WebSocket traffic for navigation.datetime values containing shell metacharacters or command sequences
• Implement process monitoring to detect unexpected child processes spawned by the Signal K server
• Review Signal K server logs for error messages related to datetime processing failures
• Deploy network intrusion detection rules to identify command injection patterns in WebSocket payloads

Monitoring Recommendations

• Enable verbose logging on Signal K Server to capture all incoming delta messages
• Configure alerts for datetime values that do not match ISO 8601 format patterns
• Monitor for outbound network connections from the Signal K server that may indicate reverse shells
• Implement file integrity monitoring on the Signal K server host system

How to Mitigate CVE-2026-23515

Immediate Actions Required

• Upgrade Signal K Server to version 1.5.0 or later immediately
• If upgrading is not immediately possible, disable the set-system-time plugin
• Ensure security is enabled on the Signal K server to require authentication
• Restrict network access to the Signal K server to trusted hosts only

Patch Information

The vulnerability is fixed in Signal K Server version 1.5.0. The patch adds strict validation of datetime format using a regular expression before the value is used in shell commands. The fix ensures that only properly formatted ISO 8601 datetime strings are accepted, rejecting any input that contains shell metacharacters or deviates from the expected format.

For detailed patch information, see the GitHub Security Advisory and the security commit.

Workarounds

• Disable the set-system-time plugin if not required for operations
• Enable authentication on the Signal K server to prevent unauthenticated exploitation
• Implement network segmentation to isolate the Signal K server from untrusted networks
• Use a reverse proxy or firewall to filter incoming WebSocket messages for malicious patterns

# Configuration example
# Disable the set-system-time plugin via Signal K Server configuration
# In the Signal K Server admin interface:
# 1. Navigate to Server -> Plugin Config
# 2. Locate "set-system-time" plugin
# 3. Disable the plugin until patched version is installed

# Alternatively, ensure security is enabled in settings.json:
# "security": {
#   "strategy": "./tokensecurity",
#   "allowNewUserRegistration": false
# }

# Restrict network access using iptables (example)
iptables -A INPUT -p tcp --dport 3000 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 3000 -j DROP