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

Summary rexmediapool::isAllowedExtension in redaxo/src/addons/mediapool/lib/mediapool.php accepts filenames that contain a blocked extension as a non-terminal segment of a longer extension chain, for example shell.php.any.jpg. The check only catches the blocked extension when it appears at the en...