CVE-2026-25728
📋 TL;DR
ClipBucket v5 versions before 5.5.3 - #40 have a TOCTOU race condition in avatar/background image uploads. Attackers can upload malicious PHP files that execute arbitrary code before validation deletes them. This affects all ClipBucket v5 installations with upload functionality enabled.
💻 Affected Systems
- ClipBucket v5
📦 What is this software?
Clipbucket by Oxygenz
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise, data theft, or ransomware deployment.
Likely Case
Webshell installation allowing persistent access, data exfiltration, or lateral movement within the network.
If Mitigated
File upload attempts logged but blocked, with no successful exploitation.
🎯 Exploit Status
Exploitation requires authenticated user access and precise timing.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 5.5.3 - #40
Vendor Advisory: https://github.com/MacWarrior/clipbucket-v5/security/advisories/GHSA-xq7c-m5r2-9wqj
Restart Required: No
Instructions:
1. Backup your installation. 2. Update to version 5.5.3 - #40 via git pull or manual patch. 3. Verify the fix by checking the commit hash includes 09536e6e2ca6d69a2ee83190b588c0b8116dd16d.
🔧 Temporary Workarounds
Disable file uploads
allTemporarily disable avatar and background image upload functionality.
Web server file extension blocking
linuxConfigure web server to block execution of .php files in upload directories.
For Apache: Add 'php_flag engine off' to .htaccess in upload directories
For Nginx: Add 'location ~ \.php$ { deny all; }' to upload directory config
🧯 If You Can't Patch
- Implement strict file upload validation before moving files to web-accessible locations.
- Use file system permissions to prevent execution in upload directories.
🔍 How to Verify
Check if Vulnerable:
Check if your ClipBucket version is below 5.5.3 - #40 and review upload handling code for TOCTOU pattern.Check Version:
Check version in ClipBucket admin panel or review CHANGELOG.md file.Verify Fix Applied:
Verify installation includes commit 09536e6e2ca6d69a2ee83190b588c0b8116dd16d and test upload functionality.📡 Detection & Monitoring
Log Indicators:
- Multiple rapid upload attempts with .php extensions
- Failed validation logs followed by file deletion
- Unexpected file execution in upload directories
Network Indicators:
- HTTP POST requests to upload endpoints with suspicious timing patterns
- Outbound connections from web server to unknown IPs
SIEM Query:
source="web_logs" AND (uri_path="/upload" OR uri_path="/avatar_upload") AND (file_extension=".php" OR response_code=500)