CVE-2025-62002

Executive Summary

CVE-2025-62002 is a medium-severity vulnerability in BullWall Ransomware Containment that allows an authenticated attacker to bypass detection thresholds by encrypting a single, potentially large file. The product monitors the number of files modified to trigger a containment response; however, if thresholds are configured to require multiple file changes, an attacker can evade detection by encrypting only one file. This weakness undermines the core detection mechanism of the ransomware containment solution.

Affected Ecosystem: This vulnerability is specific to the BullWall Ransomware Containment product, a proprietary security solution. It is not related to WordPress, Apache, or Nginx.

Impact: An authenticated attacker with network access can encrypt a single large file without triggering the containment response, potentially leading to data loss or extortion. The CVSS score of 4.3 reflects the low attack complexity but limited impact (no confidentiality or availability impact, only integrity).

Patch Status: As of this report, no official patch has been released. Users are advised to configure detection thresholds to the lowest practical value (e.g., 1 file) and monitor for anomalous file modification patterns.

CVSS Breakdown & Threat Level

• CVSS Score: 4.3 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
• Attack Vector (AV): Network – The attacker can exploit this vulnerability remotely.
• Attack Complexity (AC): Low – No special conditions are required.
• Privileges Required (PR): Low – The attacker must have valid credentials.
• User Interaction (UI): None – No user action is needed.
• Scope (S): Unchanged – The vulnerable component is the only affected component.
• Confidentiality (C): None – No data exposure.
• Integrity (I): Low – The attacker can modify a single file.
• Availability (A): None – No denial of service.

Threat Level: Medium. The vulnerability requires authentication but allows bypass of a core security control. The EPSS score of 0.0% suggests low exploitation activity in the wild, but this may change as details become public.

Deep Dive & Mechanics

BullWall Ransomware Containment is designed to detect ransomware by monitoring the number of files modified within a time window. When the number of modified files exceeds a configurable threshold, the system triggers a containment action (e.g., isolating the host or blocking the process).

The vulnerability lies in the threshold logic: if the threshold is set to require multiple file changes (e.g., 5 files), an attacker can encrypt a single large file (e.g., a database or backup file) without triggering detection. The product does not consider the size or significance of the modified file, only the count.

Attack Scenario:

1. An authenticated attacker gains access to the BullWall management interface or a monitored endpoint.
2. The attacker identifies the configured threshold (e.g., 3 files).
3. The attacker encrypts a single large file (e.g., critical_database.bak).
4. The containment system does not trigger because only one file was modified.
5. The attacker can then demand ransom for the encrypted file.

Root Cause: The detection mechanism relies solely on file count, not on file size, entropy, or other indicators of ransomware activity. This is a classic protection mechanism failure (CWE-693).

Vulnerable vs. Patched Code

Since no patch is available, we compare the vulnerable logic to a hypothetical secure implementation.

Vulnerable Logic (Pseudocode):

def check_ransomware(file_changes):
    if len(file_changes) >= THRESHOLD:
        trigger_containment()
    else:
        # No action taken
        pass

Patched Logic (Hypothetical):

def check_ransomware(file_changes):
    # Consider file size and entropy
    for change in file_changes:
        if change.file_size > LARGE_FILE_THRESHOLD and change.entropy > HIGH_ENTROPY_THRESHOLD:
            trigger_containment()
            return
    if len(file_changes) >= THRESHOLD:
        trigger_containment()

The patched version adds checks for file size and entropy, which are common indicators of encryption.

Exploitation & Lab Setup

Red Team (Attacker)

Prerequisites:

• Valid credentials for the BullWall management interface or a monitored endpoint.
• Network access to the target.

Steps:

1. Reconnaissance: Identify the BullWall threshold configuration. This may be visible in the management UI or via API.
2. Select Target: Choose a single large file (e.g., C:\Backups\database.bak).
3. Encrypt File: Use a ransomware simulator or custom script to encrypt the file.

   # Example: Encrypt a single file using AES
   from Crypto.Cipher import AES
   import os
   
   key = os.urandom(32)
   cipher = AES.new(key, AES.MODE_EAX)
   with open('target_file.bak', 'rb') as f:
       plaintext = f.read()
   ciphertext, tag = cipher.encrypt_and_digest(plaintext)
   with open('target_file.bak.enc', 'wb') as f:
       f.write(cipher.nonce + tag + ciphertext)
   os.remove('target_file.bak')
   

4. Verify Bypass: Confirm that no containment action was triggered.

Blue Team (Defender)

Detection:

• Monitor for single large file modifications with high entropy.
• Alert on file rename patterns (e.g., .bak to .bak.enc).

Mitigation:

• Configure BullWall threshold to 1 file (lowest possible).
• Enable additional detection layers (e.g., file entropy monitoring, process behavior analysis).
• Restrict access to the BullWall management interface.

Lab Setup:

• Install BullWall Ransomware Containment in a test environment.
• Configure threshold to 3 files.
• Use a ransomware simulator (e.g., from Atomic Red Team) to encrypt a single large file.
• Observe that no alert is generated.

Indicators of Compromise (IOCs)

• File Modifications:
  • Single large file (e.g., >100 MB) modified with high entropy.
  • File extension changed to .enc, .locked, or similar.
• Network Traffic:
  • Connections to BullWall management interface from unusual IPs.
• Process Behavior:
  • Processes performing file encryption on a single file (e.g., openssl, custom encryptors).
• Logs:
  • BullWall logs showing no containment action despite file modifications.

Detection Engineering

YARA Rule

rule Detect_Single_File_Encryption {
    meta:
        description = "Detects encryption of a single large file, indicative of CVE-2025-62002 bypass"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-62002"
    strings:
        $aes_key = /[A-Za-z0-9+/]{32,}/  // Base64-encoded 256-bit key
        $enc_ext = ".enc" nocase
        $locked_ext = ".locked" nocase
    condition:
        (uint32(0) == 0x464c457f) and  // ELF header (Linux)
        (for any of ($enc_ext, $locked_ext) : (# > 0)) and
        (filesize < 10000000)  // Small file size (encryptor)
}

Sigma Rule

title: BullWall Ransomware Containment Bypass - Single File Encryption
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects encryption of a single large file that may bypass BullWall thresholds
author: Valters IT
date: 2025-04-10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2025-62002
logsource:
    product: windows
    service: sysmon
detection:
    selection:
        EventID: 11  # FileCreate
        TargetFilename|endswith: '.enc'
        TargetFilename|contains: '\\Backups\\'
    condition: selection
falsepositives:
    - Legitimate file encryption tools (e.g., BitLocker)
level: medium

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"BullWall CVE-2025-62002 - Potential Ransomware Traffic"; flow:to_server,established; content:"|00 00 00 00|"; depth:4; offset:0; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Configure Threshold to 1: Set the BullWall file modification threshold to 1 to detect any single file change.
2. Enable Additional Monitoring: Deploy file integrity monitoring (FIM) and entropy-based detection.
3. Restrict Access: Limit access to the BullWall management interface to trusted IPs only.

Long-Term Fix:

• Await an official patch from BullWall that incorporates file size and entropy checks.
• Consider alternative ransomware containment solutions that use behavioral analysis.

Workaround:

• Use a script to monitor for single large file modifications and trigger custom alerts.

  #!/bin/bash
  # Monitor for single large file changes
  inotifywait -m -r --format '%w%f' /path/to/monitor | while read file
  do
      size=$(stat -c%s "$file")
      if [ $size -gt 100000000 ]; then  # 100 MB
          echo "ALERT: Large file modified: $file"
      fi
  done
  

Valters IT
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