YaySMTP <= 2.7.7 - Authenticated (Subscriber+) Arbitrary File Upload via Attachment Filename Extension

The YaySMTP – WP Mail SMTP with Email Logs, Tracking & Reports plugin for WordPress is vulnerable to Arbitrary File Upload in all versions up to, and including, 2.7.7 via the putFile function. This is due to insufficient file type validation in the putFile function, as sanitize_file_name() does not strip executable extensions and no allow-list, MIME check, or safe-extension rename is applied. This makes it possible for authenticated attackers, with subscriber-level access and above, to upload files that may be executable, which makes remote code execution possible. The only server-side guard is a .htaccess file containing 'Require all denied' written by writeGuards(), which is silently ignored by nginx and by Apache configured with AllowOverride None, meaning RCE is fully achievable on those server configurations.