CVE-2020-18121
📋 TL;DR
CVE-2020-18121 is a configuration vulnerability in Indexhibit CMS that allows authenticated attackers to modify PHP files, potentially leading to remote code execution. This affects all installations of Indexhibit 2.1.5 with default configurations. Attackers need valid user credentials to exploit this vulnerability.
💻 Affected Systems
- Indexhibit CMS
📦 What is this software?
Indexhibit by Indexhibit
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise through remote code execution, data theft, defacement, and lateral movement within the network.
Likely Case
Website defacement, malware deployment, credential harvesting, and backdoor installation.
If Mitigated
Limited impact with proper file permissions and web application firewalls blocking unauthorized file modifications.
🎯 Exploit Status
Exploitation requires authenticated access but is straightforward once credentials are obtained.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.1.6 or later
Vendor Advisory: https://github.com/Indexhibit/indexhibit/issues/17
Restart Required: No
Instructions:
1. Backup your current installation. 2. Download the latest version from the official repository. 3. Replace all files except your configuration and content directories. 4. Verify file permissions are properly set.
🔧 Temporary Workarounds
Restrict File Permissions
linuxSet strict file permissions to prevent unauthorized PHP file modifications
chmod 644 *.php
chmod 755 directories/
Implement WAF Rules
allConfigure web application firewall to block PHP file modification attempts
🧯 If You Can't Patch
- Implement strict access controls and multi-factor authentication for all user accounts
- Deploy file integrity monitoring to detect unauthorized PHP file changes
🔍 How to Verify
Check if Vulnerable:
Check if running Indexhibit version 2.1.5 by examining the version file or admin panelCheck Version:
grep -r 'version' /path/to/indexhibit/ or check admin panelVerify Fix Applied:
Verify installation is version 2.1.6 or later and test file modification functionality with authenticated user📡 Detection & Monitoring
Log Indicators:
- Unauthorized file modification attempts in web server logs
- PHP file write operations from user accounts
- Unusual admin panel activity
Network Indicators:
- POST requests to file modification endpoints
- Unusual file upload patterns
SIEM Query:
source="web_logs" AND (uri="*.php" AND method="POST") AND status="200"