The WPSpeed plugin for WordPress is vulnerable to Stored Cross-Site Scripting in versions up to, and including, 2.6.10 This is due to a combination of two issues in the LightImages HTML optimizer: (1) Dispatcher::runOptimize() decides whether the current request is the site's home page by comparing only the URL path from REQUEST_URI against the path of the home URL, so on a plain-permalinks install the author archive URL /?author=<ID> is treated as the home page and the LightImages optimizer runs on it; and (2) LightImages::optimize() calls html_entity_decode() across the entire serialized DOMDocument output under the default-enabled img_processing_entity_decode setting, converting any entity-encoded markup present as plain text in the page (including WordPress's rendered author title) into live HTML. This makes it possible for authenticated attackers, with Subscriber-level access and above, to store entity-encoded markup in their own nickname/display_name through the normal profile endpoint and have that markup rehydrated into executing script when any logged-out visitor loads their author archive.
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