Varnish/Nginx Proxy Caching <= 1.8.3 - Authenticated (Administrator+) Stored Cross-Site Scripting

Description

The Varnish/Nginx Proxy Caching plugin for WordPress is vulnerable to Stored Cross-Site Scripting in versions up to, and including, 1.8.3 due to insufficient input sanitization and output escaping. This makes it possible for authenticated attackers, with administrator-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. This only impacts multi-site installations and installations where unfiltered_html has been disabled.