ReactPress <= 3.4.0 - Authenticated (Subscriber+) Stored Cross-Site Scripting via 'permalink' Parameter

The ReactPress – Create React App for WordPress plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'permalink' parameter in all versions up to, and including, 3.4.0 due to insufficient input sanitization and output escaping. This makes it possible for authenticated attackers, with subscriber-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. This is possible because the permalink parameter is only passed through sanitize_url(), which does not prevent fetching attacker-controlled remote URLs whose response body — including script tags and event-handler attributes — is written verbatim to disk via file_put_contents().