CVE-2024-55025

Executive Summary

CVE-2024-55025 identifies a critical access control vulnerability in the VNC component of Weintek cMT-3072XH2 HMI (Human-Machine Interface) devices running easyweb v2.1.53 and OS v20231011. The flaw allows unauthorized attackers to bypass authentication and gain full access to the HMI system, potentially enabling remote control of industrial processes, data exfiltration, or disruption of operations. The vulnerability is classified under MITRE ATT&CK tactic T1190 (Exploit Public-Facing Application) and CWE-284 (Improper Access Control). No public exploit code or proof-of-concept is currently available, but the risk is elevated due to the lack of a vendor patch and the exposure of VNC services on industrial networks.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It affects a proprietary embedded system (Weintek HMI) and its firmware. Supply chain risks include the use of unpatched firmware in critical infrastructure, reliance on a vendor with unknown patch status, and potential for malicious actors to compromise devices during transit or deployment.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, likely due to incomplete or missing vector data. Based on the vulnerability description and typical HMI exposure, a reasonable CVSS v3.1 vector would be:

• Attack Vector (AV): Network (N) – VNC is remotely accessible.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): None (N) – Unauthenticated access.
• User Interaction (UI): None (N) – No user action needed.
• Scope (S): Unchanged (U) – Affects only the vulnerable component.
• Confidentiality (C): High (H) – Full HMI data access.
• Integrity (I): High (H) – Ability to modify HMI logic.
• Availability (A): High (H) – Can disrupt HMI operations.

Estimated CVSS Score: 9.8 (Critical)

Threat Level: Critical – Exploitation could lead to full compromise of industrial control systems, potentially causing physical damage or safety incidents.

Deep Dive & Mechanics

The vulnerability resides in the VNC (Virtual Network Computing) server component of the Weintek cMT-3072XH2 HMI. VNC is used for remote screen sharing and control. The flaw is an incorrect access control issue, meaning the VNC server does not properly enforce authentication or authorization checks before granting access to the HMI system.

Root Cause: The VNC server likely fails to validate client credentials or session tokens, allowing any network client to connect and interact with the HMI interface without proper authentication. This could be due to:

• Missing or weak authentication handshake.
• Default credentials that are not enforced.
• A logic flaw where the VNC server trusts the client after a minimal or null authentication attempt.

Attack Vector: An attacker on the same network as the HMI (or remotely if the VNC port is exposed) can connect to the VNC service (typically port 5900) and gain full control of the HMI screen, including the ability to:

• View real-time process data.
• Modify HMI screens and logic.
• Send commands to connected PLCs or other industrial devices.
• Disable alarms or safety functions.

Impact: Unauthorized access to an HMI can lead to:

• Operational Disruption: Changing setpoints or stopping processes.
• Safety Incidents: Manipulating safety-critical parameters.
• Data Theft: Exfiltration of proprietary process data.
• Lateral Movement: Using the HMI as a pivot to attack other ICS devices.

Vulnerable vs. Patched Code

No patched version is available. The vulnerable code is in the VNC server implementation of easyweb v2.1.53. A hypothetical patch would involve:

• Vulnerable Code (Conceptual):

  // VNC server accepts connection without proper authentication
  void vnc_handle_client(int client_sock) {
      // Missing authentication check
      vnc_send_framebuffer(client_sock);
      vnc_handle_input(client_sock);
  }
  

• Patched Code (Conceptual):

  void vnc_handle_client(int client_sock) {
      if (!vnc_authenticate(client_sock)) {
          vnc_send_error(client_sock, "Authentication failed");
          close(client_sock);
          return;
      }
      vnc_send_framebuffer(client_sock);
      vnc_handle_input(client_sock);
  }
  

The patch would enforce a mandatory authentication step (e.g., password challenge) before allowing any VNC operations.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Target Weintek cMT-3072XH2 with easyweb v2.1.53 and VNC exposed.
• Network access to port 5900.

Exploitation Steps:

1. Scan for VNC Services:

   nmap -p 5900 --open <target_ip>
   

2. Connect using any VNC client:

   vncviewer <target_ip>::5900
   

   If no authentication prompt appears, the vulnerability is confirmed.
3. Automated Exploit (Conceptual):

   import socket
   import struct
   
   def exploit_vnc(ip, port=5900):
       sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
       sock.connect((ip, port))
       # VNC handshake - skip authentication
       sock.send(b"RFB 003.008\n")
       data = sock.recv(1024)
       # If no auth required, proceed
       print("[+] Connected without authentication")
       # Send mouse/keyboard events to control HMI
       sock.close()
   
   exploit_vnc("192.168.1.100")
   

Lab Setup:

• Use a virtualized HMI environment (if available) or a real cMT-3072XH2 in an isolated lab.
• Configure the HMI with default settings.
• Ensure VNC is enabled and accessible from the attacker machine.

Blue Team (Detection & Defense)

Detection:

• Monitor for VNC connections (port 5900) from unexpected IPs.
• Look for multiple failed authentication attempts (if any) or direct connections without handshake.
• Use network flow analysis to detect anomalous VNC traffic.

Defense:

• Immediate: Disable VNC if not required. If needed, restrict access via firewall rules to trusted IPs only.
• Network Segmentation: Place HMIs on a separate VLAN with strict access controls.
• Authentication: Implement a VPN or jump host for remote access.
• Monitoring: Deploy IDS/IPS rules to detect VNC exploitation attempts.

Indicators of Compromise (IOCs)

• Network:
  • VNC connections from unauthorized IPs to port 5900.
  • Unusual VNC handshake patterns (e.g., missing authentication negotiation).
• Host:
  • Unexpected changes to HMI screens or logic.
  • New user accounts or processes on the HMI (if accessible).
• Logs:
  • VNC server logs showing connections without authentication.
  • System logs indicating unauthorized access attempts.

Detection Engineering

YARA Rule

rule CVE_2024_55025_VNC_Access_Control {
    meta:
        description = "Detects VNC traffic patterns indicative of CVE-2024-55025 exploitation"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-55025"
    strings:
        $vnc_handshake = "RFB 003.008"
        $no_auth = { 00 00 00 01 }  // VNC security type: None
    condition:
        $vnc_handshake at 0 and $no_auth
}

Sigma Rule

title: CVE-2024-55025 VNC Unauthenticated Access
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects VNC connections without authentication to Weintek HMI
author: Valters IT
logsource:
    category: network_connection
    product: zeek
detection:
    selection:
        service: "vnc"
        auth_type: "none"
    condition: selection
falsepositives:
    - Legitimate VNC connections with no authentication (if configured)
level: high

Suricata Rule

alert tcp any any -> any 5900 (msg:"CVE-2024-55025 VNC Unauthenticated Access Attempt"; flow:to_server,established; content:"RFB 003.008"; depth:12; content:"|00 00 00 01|"; distance:4; within:4; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable VNC on the HMI if not required for operations.
2. Restrict network access to the VNC port using firewall rules (allow only trusted IPs).
3. Change default credentials if any authentication is enforced.
4. Monitor logs for unauthorized access attempts.

Long-term Fix:

• Contact Weintek for an official patch or firmware update.
• If no patch is available, consider replacing the HMI with a more secure alternative.
• Implement network segmentation and intrusion detection for ICS environments.

Compensating Controls:

• Use a VPN for remote HMI access.
• Deploy an application-layer firewall to inspect VNC traffic.
• Enable logging and alerting on all HMI access.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert