CVE-2021-41403
📋 TL;DR
flatCore-CMS version 2.0.8 contains dangerous function calls that allow server-side request forgery (SSRF) attacks. This vulnerability enables attackers to make arbitrary HTTP requests from the vulnerable server, potentially accessing internal systems or services. All users running flatCore-CMS 2.0.8 are affected.
💻 Affected Systems
- flatCore-CMS
📦 What is this software?
Flatcore Cms by Flatcore
⚠️ Risk & Real-World Impact
Worst Case
Attackers could pivot from the web server to internal systems, access cloud metadata services, perform port scanning, or exploit other internal vulnerabilities.
Likely Case
Attackers could access internal APIs, retrieve sensitive data from internal services, or use the server as a proxy for attacks against other systems.
If Mitigated
With proper network segmentation and egress filtering, impact would be limited to the web server itself.
🎯 Exploit Status
SSRF vulnerabilities are commonly exploited and require minimal technical skill.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.0.9 or later
Vendor Advisory: https://github.com/flatCore/flatCore-CMS/issues/60
Restart Required: No
Instructions:
1. Backup your current installation. 2. Download flatCore-CMS 2.0.9 or later from the official repository. 3. Replace vulnerable files with patched versions. 4. Verify functionality.
🔧 Temporary Workarounds
Network Egress Filtering
allRestrict outbound HTTP/HTTPS traffic from web servers to only necessary destinations.
Web Application Firewall Rules
allBlock SSRF patterns in incoming requests using WAF rules.
🧯 If You Can't Patch
- Implement strict network segmentation to isolate the web server from internal systems
- Deploy a reverse proxy with request validation to filter malicious SSRF attempts
🔍 How to Verify
Check if Vulnerable:
Check the flatCore-CMS version in the admin panel or by examining the core files for version 2.0.8.Check Version:
Check admin panel or examine includes/core.php for version informationVerify Fix Applied:
Verify the version has been updated to 2.0.9 or later and test SSRF functionality is blocked.📡 Detection & Monitoring
Log Indicators:
- Unusual outbound HTTP requests from web server
- Requests to internal IP addresses or localhost
- Multiple failed connection attempts to various ports
Network Indicators:
- Web server making unexpected HTTP requests to internal systems
- Traffic to cloud metadata endpoints (169.254.169.254)
SIEM Query:
source="web_server" AND (dest_ip=127.0.0.1 OR dest_ip=169.254.169.254 OR dest_ip IN [internal_ranges])