CVE-2021-38753
📋 TL;DR
CVE-2021-38753 is a critical unrestricted file upload vulnerability in Simple Image Gallery Web App that allows attackers to upload malicious files like web shells. This can lead to remote code execution and complete server compromise. Anyone running vulnerable versions of this web application is affected.
💻 Affected Systems
- Simple Image Gallery Web App
📦 What is this software?
Simple Image Gallery Web App by Simple Image Gallery Web App Project
⚠️ Risk & Real-World Impact
Worst Case
Full server compromise with attacker gaining root/admin access, data theft, ransomware deployment, and use as pivot point for lateral movement.
Likely Case
Web shell upload leading to data exfiltration, defacement, cryptocurrency mining, or botnet recruitment.
If Mitigated
Attack blocked at web application firewall level with no successful file upload.
🎯 Exploit Status
Simple file upload bypass techniques can be used. No authentication required in default configuration.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check GitHub repository for latest patched version
Vendor Advisory: https://github.com/dumpling-soup/Simple-Image-Gallery-Web-App
Restart Required: Yes
Instructions:
1. Visit the GitHub repository
2. Download latest patched version
3. Replace vulnerable files
4. Restart web server
🔧 Temporary Workarounds
Implement file upload restrictions
allAdd server-side validation for file types, extensions, and content
Web Application Firewall rules
allBlock suspicious file uploads and PHP/executable file extensions
🧯 If You Can't Patch
- Disable file upload functionality completely
- Implement strict network segmentation and isolate the vulnerable server
🔍 How to Verify
Check if Vulnerable:
Attempt to upload a file with PHP extension or other executable format. If accepted without validation, system is vulnerable.Check Version:
Check application version in source code or configuration filesVerify Fix Applied:
Test file upload with restricted extensions - should be rejected. Verify code includes proper file validation.📡 Detection & Monitoring
Log Indicators:
- Unusual file uploads with executable extensions
- Multiple failed upload attempts
- Successful uploads of non-image files
Network Indicators:
- HTTP POST requests to upload endpoints with suspicious filenames
- Traffic patterns indicating web shell communication
SIEM Query:
source="web_server" AND (method="POST" AND uri="*upload*" AND (filename="*.php" OR filename="*.jsp" OR filename="*.asp"))