CVE-2021-43430
📋 TL;DR
This vulnerability allows unauthenticated attackers to upload malicious PHP files to BigAnt Office Messenger servers via the im_webserver component. Attackers can achieve remote code execution by uploading webshells or trojans. Organizations using BigAntSoft BigAnt Office Messenger 5.6 are affected.
💻 Affected Systems
- BigAntSoft BigAnt Office Messenger
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise with attacker gaining full control of the server, data exfiltration, ransomware deployment, and lateral movement to other systems.
Likely Case
Attackers upload webshells to establish persistent access, steal sensitive data, and use the compromised server for further attacks.
If Mitigated
Attack prevented through proper file upload validation, web application firewalls, and network segmentation limiting the impact to isolated segments.
🎯 Exploit Status
The GitHub references contain technical details and likely exploit code. The low complexity and unauthenticated nature make this easily weaponizable.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown
Vendor Advisory: Not available
Restart Required: No
Instructions:
No official patch is documented. Consider upgrading to a newer version if available or implementing workarounds.
🔧 Temporary Workarounds
Disable im_webserver component
allDisable the vulnerable im_webserver component if not required for functionality.
Check BigAnt documentation for disabling specific components
Implement file upload restrictions
allConfigure web server to block PHP file uploads through the im_webserver endpoint.
Configure .htaccess or web server rules to deny *.php uploads
🧯 If You Can't Patch
- Implement strict network segmentation to isolate BigAnt servers from critical systems
- Deploy a web application firewall (WAF) with rules to block PHP file uploads to vulnerable endpoints
🔍 How to Verify
Check if Vulnerable:
Check if BigAnt Office Messenger version is 5.6 and im_webserver component is enabled. Attempt to upload a test PHP file to the im_webserver endpoint.Check Version:
Check BigAnt administration panel or configuration files for version informationVerify Fix Applied:
Verify that PHP file uploads to im_webserver endpoints are blocked or that the component is disabled.📡 Detection & Monitoring
Log Indicators:
- Unusual file uploads to im_webserver endpoints
- PHP file execution from unexpected locations
- Webshell-like activity in access logs
Network Indicators:
- HTTP POST requests to im_webserver with PHP file uploads
- Unusual outbound connections from BigAnt server
SIEM Query:
source="bigant_logs" AND (url="*im_webserver*" AND method="POST" AND file_extension="php")