CVE-2020-20287
📋 TL;DR
This vulnerability allows attackers to upload arbitrary files to yccms 3.3 systems without proper validation, leading to remote code execution. Attackers can upload malicious files disguised as images and execute them on the server. Anyone running yccms 3.3 is affected.
💻 Affected Systems
- yccms
📦 What is this software?
Yccms by Yccms
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise allowing attackers to execute arbitrary commands, steal data, install backdoors, or pivot to other systems.
Likely Case
Webshell deployment leading to data theft, defacement, or use as a foothold for further attacks.
If Mitigated
File uploads blocked or properly validated, preventing malicious file execution.
🎯 Exploit Status
Exploit details and proof-of-concept code are publicly available in security blogs.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown
Vendor Advisory: http://www.yccms.net/
Restart Required: No
Instructions:
No official patch available. Consider upgrading to a newer version if available or implementing workarounds.
🔧 Temporary Workarounds
Implement strict file upload validation
allAdd server-side validation to restrict file uploads to specific extensions and verify file content.
Disable file upload functionality
allTemporarily disable the vulnerable xhUp function or file upload feature entirely.
🧯 If You Can't Patch
- Implement web application firewall (WAF) rules to block malicious file uploads
- Restrict network access to the yccms application to trusted sources only
🔍 How to Verify
Check if Vulnerable:
Check if running yccms version 3.3. Attempt to upload a file with a malicious extension disguised as an image.Check Version:
Check yccms configuration files or admin panel for version information.Verify Fix Applied:
Test file upload functionality with various file types to ensure only validated files are accepted.📡 Detection & Monitoring
Log Indicators:
- Unusual file uploads with non-image extensions
- Multiple failed upload attempts
- Files with suspicious names in upload directories
Network Indicators:
- HTTP POST requests to upload endpoints with unusual file types
- Traffic patterns indicating file upload exploitation
SIEM Query:
source="web_server" AND (uri="*upload*" OR uri="*xhUp*") AND (file_extension="php" OR file_extension="jsp" OR file_extension="asp")