CVE-2025-21624: Oxygenz Clipbucket RCE Vulnerability

CVE-2025-21624 Overview

CVE-2025-21624 is a critical arbitrary file upload vulnerability affecting ClipBucket V5, an open source video hosting platform built with PHP. The vulnerability exists in the Manage Playlist functionality, specifically in the playlist cover image upload feature. Due to insufficient validation of uploaded files, attackers can bypass intended restrictions and upload malicious PHP scripts instead of legitimate image files. This enables webshell deployment and arbitrary code execution on the target server.

Critical Impact

This vulnerability allows unauthenticated remote attackers to achieve complete server compromise through unrestricted file upload, enabling webshell deployment and arbitrary code execution with the privileges of the web server.

Affected Products

• Oxygenz ClipBucket V5 prior to version 5.5.1 - 239
• ClipBucket V5 installations with Manage Playlist functionality enabled
• Both admin area and low-level user area interfaces are vulnerable

Discovery Timeline

• 2025-01-07 - CVE-2025-21624 published to NVD
• 2025-09-05 - Last updated in NVD database

Technical Details for CVE-2025-21624

Vulnerability Analysis

This vulnerability is classified under CWE-434 (Unrestricted Upload of File with Dangerous Type). The core issue stems from the application's failure to properly validate file types during the playlist cover image upload process. The Manage Playlist functionality accepts user-supplied files without verifying that the uploaded content matches expected image formats, allowing arbitrary file types including executable PHP scripts to be stored on the server.

The attack is particularly dangerous because it affects both administrative and standard user interfaces, meaning even low-privileged accounts can exploit this vulnerability to achieve remote code execution. Once a malicious PHP file is uploaded, an attacker can access it directly through the web server to execute arbitrary commands.

Root Cause

The root cause is inadequate server-side file type validation in the playlist cover image upload handler. The application fails to implement proper checks such as:

• MIME type validation against allowlisted image types
• File extension verification
• Content-based file type detection (magic bytes)
• Proper sanitization of upload paths

This allows attackers to craft requests that bypass any client-side restrictions and upload PHP files that the server then stores in web-accessible directories.

Attack Vector

The attack vector is network-based and can be exploited without authentication in certain configurations. An attacker crafts a malicious HTTP POST request to the playlist cover image upload endpoint, substituting a PHP webshell for the expected image file. The server accepts and stores the file without proper validation, and the attacker can then access the uploaded script directly via the web server to execute arbitrary code.

The vulnerability affects both the administrative interface and regular user functionality, expanding the potential attack surface significantly. Even users with minimal privileges can exploit this flaw to escalate to full server compromise.

         location /rss/ { \
             rewrite ^/rss/([a-zA-Z0-9].+)$ /rss.php?mode=$1&$query_string last; \
         } \
-        location /list/ { \
-            rewrite ^/list/([0-9]+)/(.*)?$ /view_playlist.php?list_id=$1 last; \
-        } \
+
         location ~ /rss$ { \
             try_files $uri /rss.php; \
         } \

Source: GitHub Commit

The security patch modifies the nginx configuration to remove vulnerable rewrite rules in the /list/ location block that could facilitate exploitation of uploaded malicious files.

 
 ########## End - Rewrite rules For SEO urls ######################
 RewriteRule	^([a-zA-Z0-9-]+)/?$ 	                view_channel.php?uid=$1&seo_diret=yes [NS]
-RewriteRule	^list/([0-9]+)/(.*)?$ 	                view_playlist.php?list_id=$1 [NS]
 
 #Error Pages
 ErrorDocument 404 /404.php

Source: GitHub Commit

This .htaccess modification removes the rewrite rule for the playlist list path, which was part of the attack surface enabling access to uploaded malicious files.

Detection Methods for CVE-2025-21624

Indicators of Compromise

• Presence of PHP files with unusual names in playlist cover image upload directories
• Web server access logs showing requests to .php files in image upload paths
• Unexpected PHP files containing common webshell signatures (e.g., eval(), system(), exec(), passthru())
• HTTP POST requests to playlist management endpoints with Content-Type mismatches (e.g., application/x-php instead of image/*)

Detection Strategies

• Implement file integrity monitoring on upload directories to detect unauthorized PHP files
• Configure web application firewall (WAF) rules to block file uploads with executable extensions to image upload endpoints
• Enable detailed logging for all file upload operations, including file names, types, and sizes
• Deploy endpoint detection and response (EDR) solutions to identify webshell execution patterns

Monitoring Recommendations

• Monitor web server error logs for PHP execution attempts in upload directories
• Set up alerts for new file creations with executable extensions in media upload paths
• Track anomalous outbound network connections from the web server that may indicate post-exploitation activity
• Review access logs for sequential patterns: file upload followed by direct access to uploaded files

How to Mitigate CVE-2025-21624

Immediate Actions Required

• Upgrade ClipBucket V5 to version 5.5.1 - 239 or later immediately
• Audit upload directories for any suspicious PHP files and remove unauthorized scripts
• Review web server access logs for evidence of exploitation attempts
• Consider temporarily disabling playlist cover image upload functionality until patched

Patch Information

The vulnerability is fixed in ClipBucket V5 version 5.5.1 - 239. The security patch addresses the file upload validation issue by implementing proper file type checks. Technical details and the patch commit are available in the GitHub Security Advisory and the GitHub Commit.

Workarounds

• Configure web server to deny PHP execution in upload directories using .htaccess or nginx configuration
• Implement server-side file type validation at the web server level before requests reach the application
• Restrict upload directory permissions to prevent PHP execution
• Use a web application firewall to filter malicious file uploads

# Apache .htaccess configuration to block PHP execution in upload directories
# Add this to your uploads directory .htaccess file
<FilesMatch "\.php$">
    Require all denied
</FilesMatch>

# Alternatively, disable PHP handler for upload directory
php_flag engine off