CVE-2026-26997: Oxygenz Clipbucket XSS Vulnerability

CVE-2026-26997 Overview

CVE-2026-26997 is a Stored Cross-Site Scripting (XSS) vulnerability affecting ClipBucket v5, an open source video sharing platform. This vulnerability allows a normal authenticated user to store a malicious XSS payload that is subsequently triggered when an administrator views the affected content. The issue has been addressed in version 5.5.3 #59.

Critical Impact

Authenticated users can inject persistent XSS payloads that execute in administrator sessions, potentially leading to session hijacking, privilege escalation, or unauthorized administrative actions.

Affected Products

• Oxygenz ClipBucket versions prior to 5.5.3 #59
• ClipBucket v5 video sharing platform installations

Discovery Timeline

• 2026-02-27 - CVE-2026-26997 published to NVD
• 2026-03-03 - Last updated in NVD database

Technical Details for CVE-2026-26997

Vulnerability Analysis

This Stored XSS vulnerability (CWE-79) exists in ClipBucket v5 due to insufficient input sanitization when handling user-supplied content. The attack chain involves a low-privileged authenticated user storing a malicious payload that persists in the application's database. When an administrator subsequently views this content through the back office interface, the XSS payload executes within the administrator's browser context.

The vulnerability is particularly concerning because it targets administrative users, who have elevated privileges within the ClipBucket platform. A successful exploitation could allow attackers to perform actions on behalf of the administrator, steal session tokens, or modify system configurations.

Root Cause

The root cause of this vulnerability stems from two primary issues:

1. Insufficient authentication validation: The original code used a less robust user_id() function for authentication checks instead of the proper User::getInstance()->isUserConnected() method
2. Missing output encoding: User-supplied content such as element names was displayed directly without proper sanitization using the display_clean() function

Attack Vector

The attack is network-based and requires the attacker to have authenticated access to the ClipBucket platform with a standard user account. The attacker stores a malicious XSS payload through normal user functionality, and the payload is triggered passively when an administrator views the flagged or affected content in the back office. User interaction (administrator viewing the content) is required for successful exploitation.

The following patch demonstrates the fix applied to the authentication mechanism in upload/actions/add_to_collection.php:

 $type = $_POST['type'];
 $cid = $_POST['cid'];
 $id = $_POST['obj_id'];
-if (!user_id()) {
+if (!User::getInstance()->isUserConnected()) {
     e(lang('you_not_logged_in'));
 } elseif (empty($type) || empty($cid) || empty($id)) {
     e(lang('missing_params'));

Source: GitHub Commit 2da4c8e

The following patch shows the output encoding fix applied in the admin template upload/admin_area/styles/cb_2014/layout/flagged_item.html:

                 <td>
                     <div class="col-md-6">
                         <div class="row">
-                            <a href="{{$links.bo}}">{$flagged_item.element_name}</a>
+                            <a href="{{$links.bo}}">{display_clean($flagged_item.element_name)}</a>
                         </div>
                         <div class="row">
                             {if $type=='photo' && $flagged_item.is_photo_orphan}

Source: GitHub Commit 2da4c8e

Detection Methods for CVE-2026-26997

Indicators of Compromise

• Presence of encoded or obfuscated JavaScript in user-generated content fields such as video titles, descriptions, or collection names
• Unexpected <script> tags or event handlers (e.g., onerror, onload) in database records for user-submitted content
• Administrator session anomalies including unexpected actions or access from unusual IP addresses

Detection Strategies

• Implement Web Application Firewall (WAF) rules to detect common XSS patterns in POST requests to ClipBucket endpoints
• Monitor database fields storing user content for suspicious JavaScript or HTML injection patterns
• Enable Content Security Policy (CSP) headers to detect and report inline script execution attempts

Monitoring Recommendations

• Review administrator session logs for unusual activity patterns that may indicate session compromise
• Monitor for unauthorized administrative actions following user content submissions
• Implement logging for all user content submissions to enable forensic analysis if exploitation is suspected

How to Mitigate CVE-2026-26997

Immediate Actions Required

• Upgrade ClipBucket v5 to version 5.5.3 #59 or later immediately
• Review existing user-submitted content in the database for potential stored XSS payloads
• Consider temporarily restricting access to the administrative back office until the patch is applied

Patch Information

Oxygenz has released a security patch in ClipBucket v5 version 5.5.3 #59 that addresses this vulnerability. The patch implements proper authentication checks using User::getInstance()->isUserConnected() and adds output encoding via the display_clean() function for user-supplied content displayed in the admin interface.

For detailed patch information, refer to the GitHub Security Advisory GHSA-97r6-4hmx-hcrh and the associated commit.

Workarounds

• Implement a Web Application Firewall (WAF) with XSS filtering rules as a temporary mitigation
• Restrict user registration and content submission capabilities until patching is complete
• Enforce Content Security Policy (CSP) headers to prevent inline script execution

# Example: Add CSP headers in Apache configuration
Header set Content-Security-Policy "default-src 'self'; script-src 'self'; object-src 'none';"