The Text Toggle plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'title' shortcode attribute of the [tt_part] and [tt] shortcodes in all versions up to and including 1.1. This is due to insufficient input sanitization and output escaping on user-supplied shortcode attributes. Specifically, in the avp_texttoggle_part_shortcode() function, the 'title' attribute is extracted from shortcode attributes and concatenated directly into HTML output without any escaping — both within an HTML attribute context (title="...") on line 116 and in HTML content on line 119. While the 'class' attribute is properly validated using ctype_alnum(), the 'title' attribute has no sanitization whatsoever. An attacker can inject double-quote characters to break out of the title attribute and inject arbitrary HTML attributes including event handlers. 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.