Fastcache by Host.it <= 1.7.4 - Authenticated (Administrator+) Code Injection via .htaccess Directive Injection via 'cache_cookie_exclude' Setting

The Fastcache by Host.it plugin for WordPress is vulnerable to Code Injection in all versions up to, and including, 1.7.4 via the fastcache_settings[cache_cookie_exclude][] parameter. This is due to the plugin registering the cache_cookie_exclude setting via register_setting() without a sanitize_callback, while buildSiteHtaccessRules() applies only trim() to each cookie value before interpolating it directly into an Apache RewriteCond line — a normalization that strips surrounding whitespace but leaves embedded newlines intact, allowing an attacker to break out of the capture group and append arbitrary directives. This makes it possible for authenticated attackers, with administrator-level access and above, to inject arbitrary Apache directives into the site's .htaccess file via file_put_contents(), enabling server-level configuration changes such as setting php_value auto_prepend_file to execute attacker-controlled PHP code on every request.