The FooGallery plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'custom_attribute_key' shortcode parameter in versions up to, and including, 3.1.31 This is due to an incomplete JavaScript event handler blacklist in the foogallery_sanitize_javascript() function, which blocks only a subset of HTML event attributes (onmouseover, onmouseout, onpointerenter, onclick, onload, onchange, onerror) while permitting others such as 'onmouseenter', combined with the failure to escape the attribute key when building the gallery container HTML in foogallery_build_container_attributes_safe(). 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.