GutenKit < 2.5.1 - Contributor+ Stored CSS Injection

Description

The plugin does not validate or escape style settings saved against a post before using them to build the CSS it outputs on the front end, allowing users with the Contributor role and above to inject arbitrary CSS into pages served to other users and to anonymous visitors. JavaScript execution is not possible at that role, so the impact is limited to defacement, interface redressing and forcing external resources to load.