CVE-2020-35729
📋 TL;DR
CVE-2020-35729 is a critical OS command injection vulnerability in KLog Server 2.4.1 that allows attackers to execute arbitrary commands on the server by injecting shell metacharacters in the user parameter of authenticate.php. This affects all deployments of KLog Server 2.4.1, potentially giving attackers full control over affected systems.
💻 Affected Systems
- KLog Server
📦 What is this software?
Klog Server by Klogserver
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise allowing attackers to execute arbitrary commands with the web server's privileges, potentially leading to data theft, ransomware deployment, or persistent backdoor installation.
Likely Case
Remote code execution leading to server takeover, credential harvesting, and lateral movement within the network.
If Mitigated
Limited impact if proper input validation and command sanitization are implemented, restricting attackers to error messages or partial system information disclosure.
🎯 Exploit Status
Multiple public exploit scripts are available, making this trivial to exploit. The vulnerability requires no authentication and has simple payload construction.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown - No official patch released
Vendor Advisory: No official vendor advisory found
Restart Required: No
Instructions:
1. Check for official updates from KLog Server vendor
2. If no patch available, implement workarounds immediately
3. Consider migrating to alternative logging solutions
🔧 Temporary Workarounds
Input Validation and Sanitization
allAdd input validation to sanitize user parameter in authenticate.php to prevent shell metacharacter injection
Modify authenticate.php to escape shell metacharacters using escapeshellarg() or similar functions
Web Application Firewall Rules
allImplement WAF rules to block requests containing shell metacharacters in the user parameter
Add WAF rule: Block requests where user parameter contains ;, |, &, $, (, ), `, ||, &&
🧯 If You Can't Patch
- Isolate KLog Server instances in a separate network segment with strict firewall rules
- Implement network-based intrusion detection to monitor for command injection attempts
🔍 How to Verify
Check if Vulnerable:
Test by sending a request to authenticate.php with shell metacharacters in user parameter (e.g., user=test;id)Check Version:
Check KLog Server configuration files or web interface for version informationVerify Fix Applied:
Attempt the same exploit after implementing fixes - should receive error or sanitized response instead of command execution📡 Detection & Monitoring
Log Indicators:
- Unusual shell commands in web server logs
- Multiple failed authentication attempts with special characters
- Commands like whoami, id, ls, cat in URL parameters
Network Indicators:
- HTTP requests to authenticate.php containing shell metacharacters
- Outbound connections from web server to unexpected destinations
SIEM Query:
source="web_logs" AND uri="*authenticate.php*" AND (user="*;*" OR user="*|*" OR user="*&*" OR user="*`*" OR user="*$(*")🔗 References
- http://packetstormsecurity.com/files/160798/Klog-Server-2.4.1-Command-Injection.html
- http://packetstormsecurity.com/files/161123/Klog-Server-2.4.1-Command-Injection.html
- http://packetstormsecurity.com/files/161410/Klog-Server-2.4.1-Command-Injection.html
- https://github.com/mustgundogdu/Research/blob/main/KLOG_SERVER/Exploit_Code
- https://github.com/mustgundogdu/Research/blob/main/KLOG_SERVER/README.md
- http://packetstormsecurity.com/files/160798/Klog-Server-2.4.1-Command-Injection.html
- http://packetstormsecurity.com/files/161123/Klog-Server-2.4.1-Command-Injection.html
- http://packetstormsecurity.com/files/161410/Klog-Server-2.4.1-Command-Injection.html
- https://github.com/mustgundogdu/Research/blob/main/KLOG_SERVER/Exploit_Code
- https://github.com/mustgundogdu/Research/blob/main/KLOG_SERVER/README.md
