CVE-2026-6249: Vvveb CMS 1.0.8 RCE Vulnerability

CVE-2026-6249 Overview

Vvveb CMS 1.0.8 contains a remote code execution vulnerability in its media upload handler that allows authenticated attackers to execute arbitrary operating system commands by uploading a PHP webshell with a .phtml extension. Attackers can bypass the extension deny-list and upload malicious files to the publicly accessible media directory, then request the file over HTTP to achieve full server compromise.

Critical Impact

Authenticated attackers can achieve complete server compromise by uploading malicious PHP files disguised with the .phtml extension, bypassing the media upload security controls and executing arbitrary commands on the underlying operating system.

Affected Products

• Vvveb CMS version 1.0.8

Discovery Timeline

• 2026-04-20 - CVE-2026-6249 published to NVD
• 2026-04-21 - Last updated in NVD database

Technical Details for CVE-2026-6249

Vulnerability Analysis

This vulnerability (CWE-434: Unrestricted Upload of File with Dangerous Type) exists in the media upload handler of Vvveb CMS. The application implements an extension deny-list to prevent malicious file uploads, but fails to include the .phtml extension in this list. PHP's Apache module is typically configured to process .phtml files as PHP code, making this a viable attack path for remote code execution.

When an authenticated user uploads a file through the media library, the application checks the file extension against a predefined deny-list. Since .phtml was not included in this list, attackers could upload a PHP webshell with this extension. Once uploaded to the publicly accessible media directory, the attacker can simply request the file via HTTP to execute arbitrary PHP code with the privileges of the web server process.

Root Cause

The root cause is an incomplete extension deny-list in the system/traits/media.php file. The $uploadDenyExtensions array blocked common executable extensions like php, js, exe, and html, but omitted the .phtml extension which is also executed as PHP code by default Apache configurations. This oversight allows attackers to bypass the intended security control.

Attack Vector

The attack requires network access and low-privilege authentication to the Vvveb CMS administrative interface. Once authenticated, the attacker uploads a PHP webshell file with a .phtml extension through the media upload functionality. The file is stored in the publicly accessible media directory without modification. The attacker then makes an HTTP request directly to the uploaded file's URL, causing the web server to execute the PHP code within, granting the attacker command execution capabilities on the server.

 use Vvveb\System\Event;
 
 trait Media {
-	public $uploadDenyExtensions = ['php', 'svg', 'js', 'exe', 'html'];
+	public $uploadDenyExtensions = ['php', 'svg', 'js', 'exe', 'html', 'phtml'];

 	public $uploadDenyMime    = ['image/svg', 'image/svg+xml', 'application/javascript', 'application/x-msdownload'];

Source: GitHub Commit 23ac0e8c

Detection Methods for CVE-2026-6249

Indicators of Compromise

• Presence of .phtml files in the Vvveb CMS media upload directories (/public/media/ or similar)
• Web server access logs showing requests to .phtml files in media directories followed by suspicious activity
• New or unfamiliar files with executable PHP extensions in media folders that were not uploaded by legitimate users

Detection Strategies

• Monitor web server access logs for HTTP requests to .phtml files in media directories
• Implement file integrity monitoring on the media upload directories to detect newly uploaded executable files
• Review authentication logs for unusual media upload activity, particularly targeting administrative accounts
• Deploy web application firewalls (WAF) with rules to detect webshell upload attempts

Monitoring Recommendations

• Enable detailed logging for all file upload operations in Vvveb CMS
• Configure SIEM alerts for new .phtml file creation events in web application directories
• Implement real-time file scanning on upload directories to detect potential webshells based on content analysis

How to Mitigate CVE-2026-6249

Immediate Actions Required

• Update Vvveb CMS to a version that includes the security patch (commit 23ac0e8c758d80f3c4d9224763c8b2359648270e or later)
• Scan existing media directories for any .phtml files and remove any suspicious uploads
• Review web server access logs for evidence of exploitation attempts
• Consider temporarily disabling the media upload functionality until the patch is applied

Patch Information

The vulnerability has been addressed in a commit to the Vvveb CMS repository. The fix adds .phtml to the $uploadDenyExtensions array in system/traits/media.php, preventing uploads of files with this extension. Users should apply the patch from the GitHub commit or update to a version that includes this fix.

For more technical details, refer to the VulnCheck Advisory on Vvveb.

Workarounds

• Manually add 'phtml' to the $uploadDenyExtensions array in system/traits/media.php
• Configure the web server to not execute .phtml files in media upload directories
• Implement additional server-side validation to check file content rather than relying solely on extension-based filtering

# Apache configuration to prevent PHP execution in media directory
<Directory "/var/www/vvveb/public/media">
    php_admin_flag engine off
    RemoveHandler .php .phtml .phar
    <FilesMatch "\.(php|phtml|phar)$">
        Require all denied
    </FilesMatch>
</Directory>