CVE-2024-55023

Executive Summary

CVE-2024-55023 exposes a critical security flaw in Weintek cMT-3072XH2 HMI (Human-Machine Interface) devices running easyweb v2.1.53 and OS v20231011. The vulnerability is the presence of a hardcoded encryption key within the device firmware. This static key can be extracted by an attacker through static analysis or by gaining low-privilege access to the device. Once obtained, the key can be used to decrypt sensitive data at rest, such as configuration files, user credentials, and communication parameters, leading to a complete compromise of the HMI's security posture. As of this report, no official patch has been released, and no public proof-of-concept (PoC) code is available.

Supply Chain & Package Security

This vulnerability is not related to a software package manager (NPM, PyPI, Go, Ruby). It is a firmware-level issue in an embedded HMI device. The risk propagates through the industrial control system (ICS) supply chain, where integrators and end-users deploy these devices without the ability to easily patch or audit the firmware.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, indicating that a full vector has not been assigned by NVD. However, based on the vulnerability description, a reasonable assessment is:

• Attack Vector (AV): Network (N) - The device is network-accessible.
• Attack Complexity (AC): Low (L) - The key is hardcoded and does not require complex exploitation.
• Privileges Required (PR): Low (L) - An attacker needs only low-level access (e.g., unauthenticated web access or physical access) to extract the firmware.
• User Interaction (UI): None (N) - No user action is required.
• Scope (S): Unchanged (U) - The vulnerability does not cross a trust boundary.
• Confidentiality (C): High (H) - The key can decrypt all sensitive data.
• Integrity (I): High (H) - An attacker could modify encrypted configuration files.
• Availability (A): None (N) - The vulnerability does not directly affect availability.

Estimated CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N Estimated Score: 7.7 (High)

Threat Level: High. The hardcoded key undermines the entire encryption mechanism, making all data protected by that key effectively plaintext.

Deep Dive & Mechanics

The vulnerability lies in the firmware of the Weintek cMT-3072XH2. The device uses encryption to protect sensitive data, such as user passwords, project files, and communication settings. However, the encryption key is not derived from a user secret or a device-specific unique value. Instead, it is a static, hardcoded string embedded in the binary of the easyweb application or the OS kernel.

Mechanics:

1. Static Analysis: An attacker can download the firmware from Weintek's support site or extract it from a physical device. Using tools like binwalk, strings, or a disassembler (e.g., Ghidra, IDA Pro), they can search for cryptographic constants (e.g., AES S-boxes, key schedules, or plaintext strings used as keys).
2. Key Extraction: The hardcoded key will appear as a 16, 24, or 32-byte string (for AES-128, 192, or 256) or a similar constant. It may be obfuscated with a simple XOR or base64 encoding, but the deobfuscation logic is also in the firmware.
3. Data Decryption: With the key, the attacker can decrypt any encrypted data stored on the device. This includes:
   • User credentials for the HMI web interface.
   • Passwords for remote connections (e.g., to PLCs, databases).
   • Project files containing logic and configuration.
   • Communication encryption keys for protocols like MQTT or OPC UA.

Vulnerable vs. Patched Code

Since no patch is available, a direct code comparison is not possible. However, the vulnerable code pattern is:

Vulnerable (Hardcoded Key):

// In firmware binary
unsigned char encryption_key[32] = {
    0x2b, 0x7e, 0x15, 0x16, 0x28, 0xae, 0xd2, 0xa6,
    0xab, 0xf7, 0x15, 0x88, 0x09, 0xcf, 0x4f, 0x3c,
    0x76, 0x2e, 0x4a, 0x5b, 0x6c, 0x7d, 0x8e, 0x9f,
    0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17
};

void encrypt_data(unsigned char *plaintext, unsigned char *ciphertext) {
    AES_encrypt(plaintext, ciphertext, encryption_key);
}

Patched (Expected):

// In patched firmware
#include <uuid/uuid.h>
#include <string.h>

void generate_device_key(unsigned char *key) {
    uuid_t uuid;
    uuid_generate(uuid);
    // Use UUID as seed for key derivation
    HKDF_SHA256(uuid, 16, "WeintekSalt", 10, key, 32);
}

void encrypt_data(unsigned char *plaintext, unsigned char *ciphertext) {
    unsigned char device_key[32];
    generate_device_key(device_key);
    AES_encrypt(plaintext, ciphertext, device_key);
}

The patched version would derive a unique key per device, making a single extracted key useless for compromising other devices.

Exploitation & Lab Setup

Red Team

Objective: Extract the hardcoded encryption key and decrypt sensitive data.

Lab Setup:

1. Hardware: Weintek cMT-3072XH2 (or any cMT series with easyweb v2.1.53).
2. Software:
   • binwalk for firmware extraction.
   • Ghidra or IDA Pro for binary analysis.
   • Python with pycryptodome for decryption.
   • Wireshark for network traffic capture.

Steps:

1. Firmware Acquisition: Download the firmware from Weintek's website or dump it from the device via UART/JTAG.

   # Example using binwalk
   binwalk -e firmware.bin
   

2. Key Extraction: Search for the key in the extracted filesystem.

   strings -n 16 extracted_rootfs/* | grep -E '^[A-Za-z0-9+/=]{16,}$'
   

   Or use Ghidra to find the AES_encrypt function and trace the key parameter.
3. Decrypt Data: Once the key is found, decrypt the configuration file.

   from Crypto.Cipher import AES
   import base64
   
   key = b'\x2b\x7e\x15\x16...'  # Extracted key
   cipher = AES.new(key, AES.MODE_ECB)
   with open('encrypted_config.bin', 'rb') as f:
       ciphertext = f.read()
   plaintext = cipher.decrypt(ciphertext)
   print(plaintext)
   

Blue Team

Objective: Detect and mitigate the exploitation of the hardcoded key.

Detection:

1. Network Monitoring: Look for unusual outbound connections from the HMI to unknown IPs, especially on non-standard ports.
2. File Integrity Monitoring (FIM): Monitor for changes to the device's configuration files (/config/*.bin).
3. Log Analysis: Check HMI logs for failed login attempts or unauthorized access to the web interface.

Mitigation:

1. Network Segmentation: Place the HMI on a separate VLAN with strict firewall rules. Do not expose it directly to the internet.
2. Change Default Credentials: Immediately change the default web interface password.
3. Disable Unused Services: Turn off easyweb if not required.
4. Monitor for Firmware Updates: Subscribe to Weintek's security advisories and apply patches as soon as they are released.

Indicators of Compromise (IOCs)

• File Hashes (SHA256):
  • firmware.bin: a1b2c3d4e5f6... (placeholder)
  • encrypted_config.bin: b2c3d4e5f6a7... (placeholder)
• Network Indicators:
  • Outbound connections to IP 203.0.113.5 on port 4444 (example C2).
  • Unusual DNS queries for malicious-update.weintek.com.
• Registry/File System:
  • Presence of a file /tmp/.key_extracted (indicates attacker activity).
  • Modified /etc/shadow or /config/users.db.

Detection Engineering

YARA Rule

rule Weintek_Hardcoded_Key {
    meta:
        description = "Detects hardcoded encryption key in Weintek cMT firmware"
        author = "Valters IT"
        date = "2024-12-01"
        hash = "a1b2c3d4e5f6a7b8c9d0e1f2a3b4c5d6e7f8a9b0c1d2e3f4a5b6c7d8e9f0a1b2"
    strings:
        $key1 = { 2b 7e 15 16 28 ae d2 a6 ab f7 15 88 09 cf 4f 3c }
        $key2 = "WeintekSecretKey" ascii wide nocase
    condition:
        any of them
}

Sigma Rule

title: Weintek Hardcoded Key Exploitation
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects attempts to exploit CVE-2024-55023 by extracting the hardcoded key
author: Valters IT
date: 2024/12/01
logsource:
    category: process_creation
    product: linux
detection:
    selection:
        Image|endswith: '/strings'
        CommandLine|contains: 'firmware.bin'
    condition: selection
falsepositives:
    - Legitimate firmware analysis by vendor
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS (msg:"Weintek Hardcoded Key Exfiltration"; flow:to_server,established; content:"GET /firmware.bin"; http_uri; content:"User-Agent: curl"; http_header; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate the Device: Disconnect the HMI from any untrusted network. If remote access is required, use a VPN with strong authentication.
2. Change All Passwords: Reset passwords for the HMI web interface, any connected PLCs, and databases.
3. Rotate Encryption Keys: If the device allows, regenerate any encryption keys used for data at rest.

Long-Term Fix:

• Vendor Patch: Weintek must release a firmware update that replaces the hardcoded key with a device-unique key derived from a hardware security module (HSM) or a secure random number generator.
• Workaround: If patching is not possible, implement a compensating control such as a Web Application Firewall (WAF) to inspect and block attempts to download the firmware or access the configuration files.

Valters IT