CVE-2020-17363
📋 TL;DR
CVE-2020-17363 is a remote code execution vulnerability in USVN (User-friendly SVN) that allows attackers to execute arbitrary commands on the server by injecting shell metacharacters into specific parameters. This affects all USVN installations before version 1.0.9. Attackers can potentially gain full control of affected systems.
💻 Affected Systems
- USVN (User-friendly SVN)
📦 What is this software?
Usvn by Usvn
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise allowing attackers to execute arbitrary commands, steal data, install malware, pivot to other systems, and maintain persistent access.
Likely Case
Remote code execution leading to web server compromise, data exfiltration, and potential lateral movement within the network.
If Mitigated
Limited impact if proper network segmentation, web application firewalls, and least privilege principles are implemented.
🎯 Exploit Status
Exploitation requires sending specially crafted HTTP requests with shell metacharacters in number_start or number_end parameters.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 1.0.9
Vendor Advisory: https://github.com/usvn/usvn/releases/tag/1.0.9
Restart Required: Yes
Instructions:
1. Backup your USVN installation and data. 2. Download USVN 1.0.9 or later from the official repository. 3. Replace the existing installation with the patched version. 4. Restart the web server service.
🔧 Temporary Workarounds
Web Application Firewall Rule
allBlock requests containing shell metacharacters in the number_start or number_end parameters
Disable Timeline Module
allTemporarily disable or restrict access to the vulnerable Timeline module
🧯 If You Can't Patch
- Implement strict input validation and sanitization for all user inputs
- Isolate the USVN server in a DMZ with strict network access controls
🔍 How to Verify
Check if Vulnerable:
Check if USVN version is below 1.0.9 by examining the version file or web interfaceCheck Version:
Check the version.txt file in the USVN installation directory or view the web interface footerVerify Fix Applied:
Verify installation of USVN 1.0.9 or later and test that shell metacharacters in parameters no longer execute commands📡 Detection & Monitoring
Log Indicators:
- HTTP requests containing shell metacharacters (;, |, &, $, etc.) in number_start or number_end parameters
- Unusual command execution in web server logs
- Multiple failed exploitation attempts
Network Indicators:
- HTTP POST/GET requests to /timeline/lasthundredrequest with suspicious parameters
- Outbound connections from web server to unexpected destinations
SIEM Query:
source="web_server_logs" AND (uri="/timeline/lasthundredrequest" AND (param="number_start" OR param="number_end") AND value MATCHES "[;&|$`]+")