The Multi Post Carousel by Category plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'slides' shortcode attribute in all versions up to, and including, 1.4. This is due to insufficient input sanitization and output escaping on the user-supplied 'slides' parameter in the post_slides_shortcode function. This makes it possible for authenticated attackers, with Contributor-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.