CVE-2021-4451
📋 TL;DR
The NinjaFirewall WordPress plugin up to version 4.3.3 contains an authenticated PHAR deserialization vulnerability. This allows authenticated attackers to potentially execute arbitrary code or chain with other vulnerabilities if vulnerable software is present. Only WordPress sites with NinjaFirewall installed and user accounts with sufficient privileges are affected.
💻 Affected Systems
- NinjaFirewall (WP Edition)
📦 What is this software?
Ninjafirewall by Nintechnet
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise, data theft, or ransomware deployment through chained exploits.
Likely Case
Privilege escalation, arbitrary file read/write, or plugin/theme exploitation leading to site defacement or data leakage.
If Mitigated
Limited impact due to proper access controls, but still creates security exposure that could be chained with other vulnerabilities.
🎯 Exploit Status
Exploitation requires authenticated access and understanding of PHAR deserialization techniques.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 4.3.4
Vendor Advisory: https://blog.nintechnet.com/security-issue-fixed-in-ninjafirewall-wp-edition/
Restart Required: No
Instructions:
1. Log into WordPress admin panel. 2. Navigate to Plugins → Installed Plugins. 3. Find NinjaFirewall and click 'Update Now'. 4. Verify version is 4.3.4 or higher.
🔧 Temporary Workarounds
Disable NinjaFirewall Plugin
allTemporarily disable the vulnerable plugin until patching is possible.
wp plugin deactivate ninjafirewall
Restrict User Access
allLimit authenticated user accounts and implement strong access controls.
🧯 If You Can't Patch
- Implement strict user access controls and monitor authenticated user activity
- Deploy web application firewall rules to block PHAR deserialization attempts
🔍 How to Verify
Check if Vulnerable:
Check WordPress admin panel → Plugins → NinjaFirewall version. If version ≤ 4.3.3, system is vulnerable.Check Version:
wp plugin get ninjafirewall --field=versionVerify Fix Applied:
Confirm NinjaFirewall version is 4.3.4 or higher in WordPress admin panel.📡 Detection & Monitoring
Log Indicators:
- Unusual PHAR file uploads
- Suspicious authenticated user activity
- Unexpected plugin/theme file modifications
Network Indicators:
- HTTP POST requests with PHAR payloads to NinjaFirewall endpoints
SIEM Query:
source="wordpress.log" AND ("ninjafirewall" OR "phar:") AND (POST OR PUT)