CVE-2026-53599 Redaxo has a Mediapool isAllowedExtension bypass via multi-segment filename that leads to authenticated RCE on Apache mod_php multi-extension handlers

REDAXO is a PHP-based content management system. From 5.18.2 until 5.21.1, rexmediapool::isAllowedExtension in redaxo/src/addons/mediapool/lib/mediapool.php lets an authenticated backend user with mediaupload permission upload a JPEG/PHP polyglot named shell.php.any.jpg, which web servers with...