CVE-2021-20655
📋 TL;DR
This vulnerability allows remote attackers with administrator privileges in FileZen to execute arbitrary operating system commands. It affects FileZen versions V3.0.0 to V4.2.7 and V5.0.0 to V5.0.2. Attackers can potentially gain full control of affected systems through command injection.
💻 Affected Systems
- FileZen
📦 What is this software?
Filezen by Soliton
Filezen by Soliton
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise leading to data theft, ransomware deployment, lateral movement across networks, and persistent backdoor installation.
Likely Case
Unauthorized file access, data exfiltration, and installation of malware or cryptocurrency miners on vulnerable FileZen servers.
If Mitigated
Limited impact due to network segmentation, strong access controls, and monitoring that detects unusual administrator activity.
🎯 Exploit Status
Requires administrator credentials but once obtained, exploitation is straightforward. The unspecified vectors suggest multiple potential injection points.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: V4.2.8 and V5.0.3
Vendor Advisory: https://www.soliton.co.jp/support/2021/004334.html
Restart Required: Yes
Instructions:
1. Download latest version from vendor website. 2. Backup configuration and data. 3. Stop FileZen service. 4. Install updated version. 5. Restart FileZen service. 6. Verify functionality.
🔧 Temporary Workarounds
Restrict Administrator Access
allLimit administrator accounts to only trusted IP addresses and implement multi-factor authentication.
# Configure firewall rules to restrict admin interface access
# Example: iptables -A INPUT -p tcp --dport [FileZen_port] -s [trusted_IP] -j ACCEPT
# iptables -A INPUT -p tcp --dport [FileZen_port] -j DROP
Network Segmentation
allIsolate FileZen servers from critical systems and implement strict outbound filtering.
# Implement network segmentation rules
# Example: Place FileZen in DMZ or isolated VLAN
# Configure firewall to block unnecessary outbound connections
🧯 If You Can't Patch
- Implement strict monitoring of administrator account activity and command execution logs
- Deploy application-level firewall or WAF with command injection detection rules
🔍 How to Verify
Check if Vulnerable:
Check FileZen version in administration interface or configuration files. Versions V3.0.0-V4.2.7 or V5.0.0-V5.0.2 are vulnerable.Check Version:
# Check version in FileZen web interface under System Information or SettingsVerify Fix Applied:
Verify version is V4.2.8 or higher for V4 series, or V5.0.3 or higher for V5 series. Test administrator functionality remains intact.📡 Detection & Monitoring
Log Indicators:
- Unusual administrator login patterns
- OS command execution in application logs
- Multiple failed admin login attempts followed by successful login
Network Indicators:
- Unexpected outbound connections from FileZen server
- Traffic to suspicious IP addresses or domains
SIEM Query:
source="FileZen" AND (event_type="command_execution" OR user="admin" AND action="login") | stats count by src_ip, user