CVE-2021-47701
📋 TL;DR
CVE-2021-47701 is a privilege escalation vulnerability in OpenBMCS 2.4 that allows authenticated users with read-only permissions to elevate their privileges to administrative level. Attackers exploit a flaw in the update_user_permissions.php script by sending malicious HTTP POST requests. Organizations running OpenBMCS 2.4 with user management enabled are affected.
💻 Affected Systems
- OpenBMCS
📦 What is this software?
Openbmcs by Openbmcs
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise where attackers gain administrative control, modify all user permissions, access sensitive data, and potentially execute arbitrary code on the server.
Likely Case
Attackers escalate privileges to admin level, modify other user accounts, access confidential information, and maintain persistent access to the system.
If Mitigated
Limited impact with proper network segmentation, strong authentication controls, and monitoring that detects privilege escalation attempts.
🎯 Exploit Status
Exploit requires authenticated access but is simple to execute with publicly available proof-of-concept code.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Version 2.5 or later
Vendor Advisory: https://github.com/openbmcs/openbmcs/releases
Restart Required: Yes
Instructions:
1. Backup current configuration. 2. Download OpenBMCS 2.5 or later from official repository. 3. Replace existing installation with patched version. 4. Restart OpenBMCS service. 5. Verify user permissions are correctly configured.
🔧 Temporary Workarounds
Restrict access to useradmin plugin
allBlock or restrict access to the vulnerable /plugins/useradmin/ directory
# For Apache: add to .htaccess or virtual host config
<Location "/plugins/useradmin/">
Deny from all
</Location>
# For Nginx: add to server block
location /plugins/useradmin/ {
deny all;
}
Implement strict input validation
allAdd input validation to update_user_permissions.php script
# Add to update_user_permissions.php before processing POST data
if (!isset($_SESSION['admin']) || $_SESSION['admin'] !== true) {
http_response_code(403);
exit('Access denied');
}
🧯 If You Can't Patch
- Implement strict network access controls to limit who can access the OpenBMCS interface
- Enable detailed logging and monitoring for privilege escalation attempts and user permission changes
🔍 How to Verify
Check if Vulnerable:
Check if running OpenBMCS version 2.4 by examining version files or web interface. Test by attempting to access /plugins/useradmin/update_user_permissions.php with a non-admin account.Check Version:
grep -r 'version' /path/to/openbmcs/ | grep -i '2.4' || cat /path/to/openbmcs/VERSIONVerify Fix Applied:
After patching, verify version is 2.5 or later. Test that non-admin users cannot modify user permissions via the update_user_permissions.php script.📡 Detection & Monitoring
Log Indicators:
- POST requests to /plugins/useradmin/update_user_permissions.php from non-admin users
- User permission changes from non-admin accounts
- Multiple failed permission modification attempts
Network Indicators:
- HTTP POST requests to vulnerable endpoint with permission modification parameters
- Unusual user agent strings or source IPs accessing useradmin endpoints
SIEM Query:
source="web_logs" AND (url="/plugins/useradmin/update_user_permissions.php" OR url CONTAINS "useradmin") AND (user_role!="admin" OR user="readonly") AND http_method="POST"