CVE-2020-5639
📋 TL;DR
CVE-2020-5639 is a directory traversal vulnerability in FileZen file transfer software that allows remote attackers to upload arbitrary files to specific directories, potentially leading to remote code execution. This affects FileZen versions V3.0.0 through V4.2.2. Organizations using vulnerable FileZen installations are at risk of complete system compromise.
💻 Affected Systems
- FileZen
📦 What is this software?
Filezen by Soliton
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise via remote code execution, allowing attackers to install malware, exfiltrate data, pivot to other systems, or deploy ransomware.
Likely Case
Unauthorized file upload leading to web shell deployment, data theft, or service disruption.
If Mitigated
Limited impact with proper network segmentation, file integrity monitoring, and least privilege access controls in place.
🎯 Exploit Status
Directory traversal vulnerabilities are commonly exploited and weaponized. The CVSS 9.8 score indicates trivial exploitation with high impact.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: V4.2.3 and later
Vendor Advisory: https://www.soliton.co.jp/support/2020/004278.html
Restart Required: Yes
Instructions:
1. Download FileZen V4.2.3 or later from Soliton support portal. 2. Backup configuration and data. 3. Stop FileZen service. 4. Install the updated version. 5. Restart FileZen service. 6. Verify functionality.
🔧 Temporary Workarounds
Restrict File Upload Directory
allConfigure FileZen to only allow uploads to specific, non-executable directories with strict permissions.
Network Segmentation
allPlace FileZen behind a firewall with strict inbound rules, limiting access to trusted IP addresses only.
🧯 If You Can't Patch
- Implement web application firewall (WAF) rules to block directory traversal patterns in file upload requests.
- Disable FileZen's file upload functionality entirely if not required for business operations.
🔍 How to Verify
Check if Vulnerable:
Check FileZen version via admin interface or configuration files. Versions V3.0.0 through V4.2.2 are vulnerable.Check Version:
Check FileZen admin console or configuration files for version information.Verify Fix Applied:
Verify FileZen version is V4.2.3 or later. Test file upload functionality with directory traversal attempts to confirm patching.📡 Detection & Monitoring
Log Indicators:
- Unusual file upload patterns
- Directory traversal strings in request logs (e.g., '../', '..\')
- Unexpected file creation in system directories
Network Indicators:
- HTTP requests containing directory traversal sequences in file upload parameters
- Unusual outbound connections from FileZen server
SIEM Query:
source="filezen.log" AND ("../" OR "..\" OR "%2e%2e%2f")