The Categories Images plugin for WordPress is vulnerable to Stored Cross-Site Scripting in versions up to, and including, 3.3.1, via the 'z_taxonomy_image' shortcode. This is due to the shortcode rendering path passing attacker-controlled class input into a fallback image builder that concatenates HTML attributes without proper escaping. This makes it possible for authenticated attackers, with Contributor-level access and above, to inject arbitrary web scripts that execute when users interact with the injected frontend page via the 'class' shortcode attribute.