SpeedyCache <= 1.3.8 - Authenticated (Administrator+) Arbitrary File Read

The SpeedyCache plugin for WordPress is vulnerable to Arbitrary File Read via Path Traversal in all versions up to, and including, 1.3.8. This is due to a mismatch between CSS URL validation (which allows query strings like `.css?...`) and path resolution (which strips query strings), combined with no validation that the resolved file is actually a CSS file. This makes it possible for authenticated attackers, with Administrator-level access and above, to read arbitrary files from the server (including `wp-config.php` and `/etc/passwd`) by injecting crafted `<link>` tags into page content, with the file contents written to publicly accessible cache files.