CVE-2026-6257 is a critical vulnerability in Vvveb CMS v1.0.8.2 related to unrestricted file upload and renaming logic. Due to a missing return statement in the file rename handler, authenticated attackers can bypass extension restrictions by renaming uploaded files to .php or .htaccess. This allows them to inject Apache directives via a malicious .htaccess file that registers PHP-executable MIME types, followed by uploading a PHP file to execute arbitrary operating system commands with the privileges of the web server user (www-data). This vulnerability is classified under CWE-434 (Unrestricted Upload of File with Dangerous Type) and has a CVSS 4.0 score of 9.2, indicating critical severity.

Successful exploitation allows authenticated attackers to achieve remote code execution on the server running Vvveb CMS 1.0.8.2. This can lead to full compromise of the web server under the www-data user context, enabling arbitrary operating system command execution. The vulnerability bypasses file extension restrictions, facilitating the upload and execution of malicious PHP code.

No official patch or remediation is currently available for this vulnerability. Users should monitor the vendor's advisory for updates. Until a fix is released, restrict authenticated user permissions to prevent file uploads or renaming, and consider disabling or restricting the media management functionality. Implementing web server-level controls to block execution of uploaded files with dangerous extensions may also help mitigate risk.