CVE-2021-3317
📋 TL;DR
CVE-2021-3317 is an authenticated command injection vulnerability in KLog Server that allows attackers with valid credentials to execute arbitrary commands on the underlying operating system. The vulnerability exists in async.php which passes unsanitized user input from the source parameter to shell_exec(). This affects all KLog Server installations up to version 2.4.1.
💻 Affected Systems
- KLog Server
📦 What is this software?
Klog Server by Klogserver
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise leading to data exfiltration, lateral movement, ransomware deployment, or complete server takeover.
Likely Case
Privilege escalation, data theft, installation of backdoors, or disruption of logging services.
If Mitigated
Limited impact if proper network segmentation, least privilege access, and command execution restrictions are in place.
🎯 Exploit Status
Exploitation requires valid credentials but is straightforward once authenticated.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.4.2 or later
Vendor Advisory: https://docs.unsafe-inline.com/0day/klog-server-authenticated-command-injection
Restart Required: Yes
Instructions:
1. Backup current configuration and data. 2. Download latest version from official source. 3. Stop KLog Server service. 4. Install updated version. 5. Restart KLog Server service. 6. Verify functionality.
🔧 Temporary Workarounds
Input Validation Filter
allAdd input validation to sanitize the source parameter before processing
Modify async.php to validate source parameter against allowed values
WAF Rule
allBlock malicious patterns in source parameter requests
Add WAF rule to block shell metacharacters in source parameter
🧯 If You Can't Patch
- Implement strict network segmentation to isolate KLog Server from critical systems
- Enforce strong authentication policies and monitor for suspicious login attempts
🔍 How to Verify
Check if Vulnerable:
Check KLog Server version in web interface or configuration filesCheck Version:
grep -i version /path/to/klog/config/files or check web interfaceVerify Fix Applied:
Verify version is 2.4.2 or later and test source parameter with shell metacharacters📡 Detection & Monitoring
Log Indicators:
- Unusual commands in system logs
- Multiple failed authentication attempts followed by successful login
- Suspicious processes spawned from KLog Server
Network Indicators:
- Outbound connections from KLog Server to unusual destinations
- Unexpected network traffic patterns
SIEM Query:
source="KLog Server" AND (cmd.exe OR bash OR sh OR powershell) OR source="KLog Server" AND (source_parameter CONTAINS "|" OR source_parameter CONTAINS ";" OR source_parameter CONTAINS "&")🔗 References
- http://packetstormsecurity.com/files/161208/Klog-Server-2.4.1-Command-Injection.html
- https://docs.unsafe-inline.com/0day/klog-server-authenticated-command-injection
- http://packetstormsecurity.com/files/161208/Klog-Server-2.4.1-Command-Injection.html
- https://docs.unsafe-inline.com/0day/klog-server-authenticated-command-injection
