The "WebSub (FKA. PubSubHubbub)" plugin for WordPress is vulnerable to Stored Cross-Site Scripting via plugin settings in all versions up to, and including, 3.1.4 due to insufficient input sanitization and output escaping. This makes it possible for authenticated attackers, with administrator-level permissions and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.