Vtiger CRM < 8.4.0 Authenticated File Upload RCE via Documents Module

Vtiger CRM before 8.4.0 contains an authenticated file upload vulnerability that allows low-privileged users to achieve remote code execution by uploading a .phar file containing arbitrary PHP code through the Documents module, bypassing the extension denylist in config.inc.php which omits the .phar extension. The uploaded file is stored with its original .phar extension under the web-accessible storage directory, and a misconfigured .htaccess using Apache 2.2 syntax is silently ignored on Apache 2.4 deployments, allowing unauthenticated HTTP requests to directly execute the uploaded PHP payload.