The Investi plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'investi-announcements-accordion' shortcode's 'maximum-num-years' attribute in all versions up to, and including, 1.0.26. This is due to insufficient input sanitization and output escaping on user-supplied shortcode attributes. Specifically, the 'maximum-num-years' attribute value is read directly from shortcode attributes and interpolated into a double-quoted HTML attribute without any escaping (no esc_attr(), htmlspecialchars(), or similar). 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.