CVE-2021-27983
📋 TL;DR
A Remote Code Execution vulnerability in MaxSite CMS v107.5 allows attackers to execute arbitrary code on affected systems through the Documents page. This affects all users running the vulnerable version of MaxSite CMS, potentially compromising the entire web server.
💻 Affected Systems
- MaxSite CMS
📦 What is this software?
Maxsite Cms by Max 3000
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise allowing attackers to install malware, steal data, pivot to internal networks, or use server for cryptocurrency mining or DDoS attacks.
Likely Case
Website defacement, data theft, installation of backdoors, and use of server resources for malicious activities.
If Mitigated
Limited impact if proper network segmentation, WAF rules, and monitoring are in place to detect and block exploitation attempts.
🎯 Exploit Status
The vulnerability is publicly documented with proof-of-concept available, making exploitation straightforward for attackers.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: v107.6 or later
Vendor Advisory: https://github.com/maxsite/cms/issues/430
Restart Required: No
Instructions:
1. Backup your current installation. 2. Download the latest version from the official MaxSite CMS repository. 3. Replace all files with the updated version. 4. Verify the Documents page functionality.
🔧 Temporary Workarounds
Disable Documents Module
linuxTemporarily disable or remove the vulnerable Documents page functionality
mv /path/to/cms/modules/documents /path/to/cms/modules/documents.disabled
WAF Rule Implementation
allImplement Web Application Firewall rules to block exploitation attempts
🧯 If You Can't Patch
- Implement strict network segmentation to isolate the vulnerable system
- Deploy intrusion detection systems and monitor for exploitation attempts
🔍 How to Verify
Check if Vulnerable:
Check if running MaxSite CMS version 107.5 by examining the CMS version in admin panel or configuration filesCheck Version:
grep -r 'version' /path/to/maxsite/cms/config/ files or check admin dashboardVerify Fix Applied:
Verify version is 107.6 or later and test Documents page functionality for any anomalies📡 Detection & Monitoring
Log Indicators:
- Unusual file uploads via Documents page
- Suspicious POST requests to documents-related endpoints
- Unexpected system command execution in web server logs
Network Indicators:
- Unusual outbound connections from web server
- Traffic patterns indicating reverse shell establishment
SIEM Query:
source="web_logs" AND (uri="/documents/*" OR uri="*/documents") AND (method="POST" OR method="PUT") AND size>100000