CVE-2020-23040
📋 TL;DR
Sky File v2.1.0 contains a directory traversal vulnerability in its FTP server that allows attackers to bypass directory restrictions using 'null' path commands. This enables unauthorized access to sensitive files and data outside the intended directory structure. Organizations using Sky File v2.1.0 with FTP server enabled are affected.
💻 Affected Systems
- Sky File
📦 What is this software?
Sky File by Sky File Project
⚠️ Risk & Real-World Impact
Worst Case
Attackers gain complete access to the server's file system, potentially stealing sensitive data, modifying critical files, or planting backdoors for persistent access.
Likely Case
Attackers access sensitive configuration files, user data, or application files that could lead to further compromise or data exfiltration.
If Mitigated
Limited impact with proper network segmentation, file system permissions, and monitoring in place to detect traversal attempts.
🎯 Exploit Status
Exploitation requires FTP access but no authentication bypass. The vulnerability is well-documented with proof-of-concept available.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: v2.1.1 or later
Vendor Advisory: https://www.vulnerability-lab.com/get_content.php?id=2207
Restart Required: Yes
Instructions:
1. Download the latest version from the official Sky File repository. 2. Backup current configuration and data. 3. Stop the Sky File service. 4. Install the updated version. 5. Restart the service and verify functionality.
🔧 Temporary Workarounds
Disable FTP Server
linuxTemporarily disable the FTP server functionality if not required.
systemctl stop skyfile-ftp
chmod -x /usr/bin/skyfile-ftp
Restrict FTP Access
linuxConfigure firewall rules to limit FTP access to trusted IP addresses only.
iptables -A INPUT -p tcp --dport 21 -s TRUSTED_IP -j ACCEPT
iptables -A INPUT -p tcp --dport 21 -j DROP
🧯 If You Can't Patch
- Implement strict file system permissions to limit what the FTP service account can access.
- Deploy network segmentation to isolate the FTP server from sensitive systems and data.
🔍 How to Verify
Check if Vulnerable:
Check if Sky File version is 2.1.0 and FTP server is enabled. Test FTP access with null path commands to attempt directory traversal.Check Version:
skyfile --versionVerify Fix Applied:
After patching, attempt the same null path traversal commands via FTP to confirm they are blocked. Verify version shows 2.1.1 or later.📡 Detection & Monitoring
Log Indicators:
- FTP logs showing 'null' or '../' sequences in path commands
- Failed or successful file access attempts outside expected directories
Network Indicators:
- Unusual FTP traffic patterns, especially to non-standard paths
- Multiple failed FTP login attempts followed by successful traversal
SIEM Query:
source="ftp.log" AND ("null" OR "../" OR "..\")