CVE-2021-40098
📋 TL;DR
This vulnerability in Concrete CMS allows attackers to perform path traversal attacks through external forms, leading to remote code execution. It affects all Concrete CMS installations through version 8.5.5. Attackers can exploit this to take full control of affected systems.
💻 Affected Systems
- Concrete CMS
📦 What is this software?
Concrete Cms by Concretecms
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise with attacker gaining full administrative access, data theft, and potential lateral movement to other systems.
Likely Case
Remote code execution leading to website defacement, data exfiltration, or installation of backdoors/malware.
If Mitigated
Limited impact with proper network segmentation and web application firewalls blocking exploitation attempts.
🎯 Exploit Status
Exploit details are publicly available on HackerOne and require minimal technical skill to execute.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 8.5.6 and later
Vendor Advisory: https://documentation.concretecms.org/developers/introduction/version-history/856-release-notes
Restart Required: No
Instructions:
1. Backup your Concrete CMS installation and database. 2. Download Concrete CMS version 8.5.6 or later. 3. Replace all files with the new version. 4. Run any database update scripts if prompted.
🔧 Temporary Workarounds
Disable External Forms
allTemporarily disable or restrict access to external forms functionality.
Web Application Firewall Rules
allImplement WAF rules to block path traversal patterns and regex manipulation attempts.
🧯 If You Can't Patch
- Implement strict network segmentation to isolate the CMS from critical systems
- Deploy a web application firewall with rules specifically blocking path traversal patterns
🔍 How to Verify
Check if Vulnerable:
Check Concrete CMS version in admin dashboard or via /concrete/config/app.php version parameter.Check Version:
Check /concrete/config/app.php for 'version' parameter or use Concrete CMS admin dashboard.Verify Fix Applied:
Confirm version is 8.5.6 or higher and test external forms functionality for path traversal.📡 Detection & Monitoring
Log Indicators:
- Unusual file access patterns in web server logs
- Requests containing '../' sequences or regex manipulation
- External form submissions with suspicious parameters
Network Indicators:
- HTTP requests with path traversal sequences to CMS endpoints
- Unusual outbound connections from CMS server
SIEM Query:
web.url:*../* AND (web.url:*concrete* OR web.url:*cms*)