CVE-2021-41243
📋 TL;DR
CVE-2021-41243 is a critical vulnerability in baserCMS that combines Zip Slip and OS command injection flaws. Authenticated users with file upload permissions can upload malicious zip files to execute arbitrary commands on the server. This affects all baserCMS installations where the management system is accessible to users with upload privileges.
💻 Affected Systems
- baserCMS
📦 What is this software?
Basercms by Basercms
⚠️ Risk & Real-World Impact
Worst Case
Full server compromise allowing attackers to execute arbitrary commands, access sensitive data, install malware, or pivot to other systems.
Likely Case
Unauthorized file system access, data exfiltration, or installation of web shells for persistent access.
If Mitigated
Limited impact with proper network segmentation, minimal user privileges, and file upload restrictions.
🎯 Exploit Status
Exploitation requires authenticated access but is straightforward once credentials are obtained.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: baserCMS 4.5.2 and later
Vendor Advisory: https://github.com/baserproject/basercms/security/advisories/GHSA-7rpc-9m88-cf9w
Restart Required: No
Instructions:
1. Backup your baserCMS installation and database. 2. Download baserCMS 4.5.2 or later from the official repository. 3. Replace the existing installation with the patched version. 4. Verify all customizations and plugins remain functional.
🔧 Temporary Workarounds
Restrict File Upload Permissions
allTemporarily remove file upload permissions from all non-essential users.
# Modify user permissions in baserCMS admin panel to disable file upload capabilities
Implement Web Application Firewall Rules
allBlock malicious zip file uploads and command injection attempts.
# WAF rules to block suspicious file uploads and command injection patterns
🧯 If You Can't Patch
- Implement strict network segmentation to isolate baserCMS from critical systems
- Enable detailed logging and monitoring for file upload activities and command execution attempts
🔍 How to Verify
Check if Vulnerable:
Check baserCMS version in admin panel or by examining the application files. Versions before 4.5.2 are vulnerable.Check Version:
# Check baserCMS version via admin interface or examine config filesVerify Fix Applied:
Confirm version is 4.5.2 or later and test file upload functionality with safe test files.📡 Detection & Monitoring
Log Indicators:
- Unusual file upload patterns
- Command execution in web server logs
- Zip file extraction to unexpected directories
Network Indicators:
- Large zip file uploads followed by outbound connections
- Unusual POST requests to file upload endpoints
SIEM Query:
source="web_server" AND (file_upload="*.zip" OR cmd_execution="*" OR path_traversal="*")🔗 References
- https://github.com/baserproject/basercms/commit/9088b99c329d1faff3a2f1269f37b9a9d8d5f6ff
- https://github.com/baserproject/basercms/security/advisories/GHSA-7rpc-9m88-cf9w
- https://github.com/baserproject/basercms/commit/9088b99c329d1faff3a2f1269f37b9a9d8d5f6ff
- https://github.com/baserproject/basercms/security/advisories/GHSA-7rpc-9m88-cf9w
