CVE-2021-25294
📋 TL;DR
CVE-2021-25294 is a critical remote code execution vulnerability in OpenCATS caused by unsafe deserialization of user input. Attackers can exploit this by sending specially crafted requests to the index.php endpoint, potentially gaining full control of affected systems. All OpenCATS users running vulnerable versions are affected.
💻 Affected Systems
- OpenCATS
📦 What is this software?
Opencats by Opencats
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise allowing attackers to execute arbitrary code, steal sensitive data, install malware, pivot to other systems, and maintain persistent access.
Likely Case
Remote code execution leading to data theft, system takeover, and potential ransomware deployment on vulnerable OpenCATS instances.
If Mitigated
Limited impact with proper network segmentation, WAF rules blocking malicious payloads, and restricted user access preventing exploitation.
🎯 Exploit Status
Exploit leverages PHP object injection via __destruct magic method in guzzlehttp, with public proof-of-concept available.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 0.9.5-4 and later
Vendor Advisory: https://www.opencats.org/news/
Restart Required: No
Instructions:
1. Backup your OpenCATS installation and database. 2. Download the latest version from the official OpenCATS repository. 3. Replace vulnerable files with patched versions. 4. Verify the fix by checking that unserialize() calls are properly sanitized.
🔧 Temporary Workarounds
Input Validation Filter
allAdd input validation to filter malicious serialized data before processing
Modify lib/DataGrid.php to validate/sanitize the 'parametersactivity:ActivityDataGrid' parameter
WAF Rule Blocking
allImplement web application firewall rules to block requests containing serialized PHP objects
Add WAF rule to block patterns like 'O:[0-9]+:"GuzzleHttp' in POST/GET parameters
🧯 If You Can't Patch
- Implement strict network access controls to limit OpenCATS access to authorized users only
- Deploy a web application firewall with rules specifically blocking PHP object injection payloads
🔍 How to Verify
Check if Vulnerable:
Check if your OpenCATS version is 0.9.5-3 or earlier by examining the version file or admin interfaceCheck Version:
grep -r 'version' /path/to/opencats/ or check admin dashboardVerify Fix Applied:
Verify that the vulnerable unserialize() call in lib/DataGrid.php has been replaced with safe deserialization or removed📡 Detection & Monitoring
Log Indicators:
- Unusual POST requests to index.php?m=activity with serialized data
- PHP errors related to unserialize() or GuzzleHttp
Network Indicators:
- HTTP requests containing serialized PHP object patterns (O:8:"stdClass" or similar)
- Unexpected outbound connections from OpenCATS server
SIEM Query:
source="web_logs" AND (uri="*index.php?m=activity*" AND (param="*O:[0-9]+:*" OR param="*GuzzleHttp*"))🔗 References
- https://github.com/snoopysecurity/snoopysecurity.github.io/blob/master/web-application-security/2021/01/16/09_opencats_php_object_injection.html
- https://snoopysecurity.github.io/web-application-security/2021/01/16/09_opencats_php_object_injection.html
- https://www.opencats.org/news/
- https://github.com/snoopysecurity/snoopysecurity.github.io/blob/master/web-application-security/2021/01/16/09_opencats_php_object_injection.html
- https://snoopysecurity.github.io/web-application-security/2021/01/16/09_opencats_php_object_injection.html
- https://www.opencats.org/news/
