CVE-2021-27817
📋 TL;DR
This CVE describes a remote code execution vulnerability in ShopXO e-commerce platform version 1.9.3. Attackers can upload malicious PHAR files disguised as JPG images, which when processed by the application can lead to arbitrary command execution. All ShopXO 1.9.3 installations are affected.
💻 Affected Systems
- ShopXO
📦 What is this software?
Shopxo by Shopxo
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise allowing attackers to execute arbitrary commands, steal sensitive data, install backdoors, or pivot to other systems.
Likely Case
Web server compromise leading to data theft, defacement, or cryptocurrency mining malware installation.
If Mitigated
Attack blocked at web application firewall level or file upload validation prevents malicious file execution.
🎯 Exploit Status
Exploit requires file upload capability and PHAR deserialization in the application.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 1.9.4 or later
Vendor Advisory: https://github.com/gongfuxiang/shopxo
Restart Required: No
Instructions:
1. Backup your ShopXO installation and database. 2. Download latest version from official GitHub repository. 3. Replace vulnerable files with patched version. 4. Verify functionality.
🔧 Temporary Workarounds
File Upload Restriction
allRestrict file uploads to prevent PHAR disguised as JPG files
Modify upload validation to check file signatures, not just extensions
Disable PHAR Deserialization
linuxPrevent PHP from processing PHAR files through deserialization
Set phar.readonly = 1 in php.ini
🧯 If You Can't Patch
- Implement strict file upload validation with MIME type checking and file signature verification
- Deploy web application firewall with rules to block PHAR file uploads and suspicious POST requests
🔍 How to Verify
Check if Vulnerable:
Check ShopXO version in admin panel or application files. Version 1.9.3 is vulnerable.Check Version:
Check application/version.php or admin panel system informationVerify Fix Applied:
Verify version is 1.9.4 or later and test file upload functionality with various file types.📡 Detection & Monitoring
Log Indicators:
- Unusual file uploads with .jpg extension but PHP/PHAR content
- POST requests to upload endpoints with suspicious payloads
- System command execution in web server logs
Network Indicators:
- HTTP POST requests with file uploads containing PHAR signatures
- Outbound connections from web server to unknown IPs
SIEM Query:
source="web_logs" AND (uri="/upload" OR uri="/admin/upload") AND (file_extension="jpg" AND content_contains="__HALT_COMPILER" OR "GIF8")