The Easy Social Photos Gallery plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'wrapper_class' shortcode attribute of the 'my-instagram-feed' shortcode in all versions up to, and including, 3.1.2. This is due to insufficient input sanitization and output escaping on user supplied attributes. Specifically, the plugin uses sanitize_text_field() instead of esc_attr() when outputting the 'wrapper_class' attribute inside a double-quoted HTML class attribute. Since sanitize_text_field() does not encode double quotes, an attacker can break out of the class attribute and inject arbitrary HTML 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.