WP Fastest Cache 0.9.0.3 - 1.5.0 - Unauthenticated Stored XSS via Host Header Cache Poisoning

Description

The plugin does not validate the Host header before using it to build the URLs of the asset files it embeds in the pages it caches, and does not include that header in the cache key, allowing unauthenticated attackers to poison cached pages with references to a server they control and have arbitrary JavaScript run for every subsequent visitor.

Its rule for withholding cached pages from administrators relies on a list of administrator usernames that is only rebuilt when a user registers or updates their profile, so an administrator promoted to the role afterwards is served the poisoned page as well and the injected script can run in an authenticated administrator session.