CVE-2021-26809
📋 TL;DR
CVE-2021-26809 is a critical remote code execution vulnerability in PHPGurukul Car Rental Project version 2.0 that allows unauthenticated attackers to upload malicious PHP shell files via the changeimage1.php endpoint. This enables complete server compromise and affects any organization running this vulnerable software version. The vulnerability stems from insufficient file upload validation (CWE-434).
💻 Affected Systems
- PHPGurukul Car Rental Project
📦 What is this software?
Car Rental Portal by Phpgurukul
⚠️ Risk & Real-World Impact
Worst Case
Complete server takeover with attacker gaining full administrative control, data exfiltration, lateral movement to other systems, and persistent backdoor installation.
Likely Case
Webshell deployment leading to data theft, website defacement, cryptocurrency mining, or use as part of a botnet.
If Mitigated
Limited impact with proper file upload restrictions, web application firewalls, and network segmentation preventing lateral movement.
🎯 Exploit Status
Multiple public exploit scripts are available that automate the shell upload process. The attack requires minimal technical skill to execute.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown - No official patch from PHPGurukul identified
Vendor Advisory: No official vendor advisory found
Restart Required: No
Instructions:
1. Remove or disable the Car Rental Project 2.0 application immediately. 2. Migrate to alternative car rental software solutions. 3. If continuing use is necessary, implement the workarounds below.
🔧 Temporary Workarounds
File Upload Restriction
allImplement strict file upload validation in changeimage1.php to only allow image file types and verify file signatures.
Modify changeimage1.php to include: $allowed_types = ['image/jpeg', 'image/png', 'image/gif']; $file_info = finfo_file(finfo_open(FILEINFO_MIME_TYPE), $_FILES['file']['tmp_name']); if(!in_array($file_info, $allowed_types)) { die('Invalid file type'); }
Disable Vulnerable Endpoint
allTemporarily disable or restrict access to changeimage1.php while implementing permanent fixes.
Rename changeimage1.php to changeimage1.php.disabled
Or add: if($_SERVER['REQUEST_URI'] == '/changeimage1.php') { header('HTTP/1.1 403 Forbidden'); exit(); } to .htaccess (Apache) or nginx config
🧯 If You Can't Patch
- Implement a Web Application Firewall (WAF) with rules blocking file uploads to changeimage1.php and detecting shell upload patterns
- Isolate the vulnerable system in a restricted network segment with no internet access and minimal internal connectivity
🔍 How to Verify
Check if Vulnerable:
Check if Car Rental Project version 2.0 is installed and accessible. Attempt to upload a test PHP file to /changeimage1.php (in a controlled environment only).Check Version:
Check application files for version indicators, typically in config files or footer: grep -r '2.0' /path/to/car-rental-project/Verify Fix Applied:
After implementing workarounds, attempt to upload a PHP file to verify it's blocked. Check that only legitimate image files can be uploaded.📡 Detection & Monitoring
Log Indicators:
- Multiple POST requests to changeimage1.php with file uploads
- Upload of files with .php extension
- Unusual file creation in upload directories
- Web server errors related to file type validation
Network Indicators:
- HTTP POST requests to */changeimage1.php with file upload content
- Outbound connections from web server to unknown IPs after file upload
SIEM Query:
source="web_server_logs" AND (uri="/changeimage1.php" OR uri LIKE "%/changeimage1.php") AND method="POST" AND (file_ext=".php" OR content_type="application/x-php")