CVE-2021-42839
📋 TL;DR
This vulnerability allows remote attackers to upload malicious scripts and execute arbitrary code on Grand Vice info Co. webopac7 systems. Attackers with general user permissions can exploit unfiltered special characters in file upload functions to gain system control or disrupt services. Organizations using vulnerable versions of webopac7 are affected.
💻 Affected Systems
- Grand Vice info Co. webopac7
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise allowing attackers to install persistent backdoors, steal sensitive data, pivot to other systems, or permanently disable services.
Likely Case
Attackers upload web shells to gain remote code execution, deface websites, install cryptocurrency miners, or exfiltrate database contents.
If Mitigated
With proper file upload validation and web application firewalls, exploitation attempts are blocked, limiting impact to failed upload attempts.
🎯 Exploit Status
Requires general user credentials. File upload vulnerabilities with code execution are commonly weaponized. No public exploit code found in references.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Not specified in available references
Vendor Advisory: https://www.twcert.org.tw/tw/cp-132-5288-9d546-1.html
Restart Required: No
Instructions:
1. Contact Grand Vice info Co. for patch information. 2. Apply vendor-provided security updates. 3. Verify file upload functions properly filter special characters.
🔧 Temporary Workarounds
Disable file upload functionality
allTemporarily disable file upload features in webopac7 until patched
Implement WAF rules
allConfigure web application firewall to block malicious file upload attempts
🧯 If You Can't Patch
- Implement strict file upload validation: allow only specific file types, enforce size limits, scan for malware
- Restrict user permissions: remove file upload capabilities from general users, implement least privilege access
🔍 How to Verify
Check if Vulnerable:
Test file upload functionality with special characters in filenames or content. Attempt to upload files with executable extensions.Check Version:
Check webopac7 version through application interface or configuration filesVerify Fix Applied:
Verify uploaded files are properly validated and special characters are filtered. Test that malicious file uploads are rejected.📡 Detection & Monitoring
Log Indicators:
- Unusual file upload activity
- Files with special characters in names
- Web shell access patterns
- Failed upload attempts with executable extensions
Network Indicators:
- HTTP POST requests to upload endpoints with suspicious content
- Outbound connections from web server to unknown IPs
SIEM Query:
source="webopac7" AND (event="file_upload" OR url="*upload*") AND (filename="*..*" OR filename="*.php" OR filename="*.jsp" OR filename="*.asp")