The Autoptimize plugin for WordPress is vulnerable to Stored Cross-Site Scripting via Comment Author Name in all versions up to, and including, 3.1.15.1 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. Exploitation requires an administrator to have enabled Autoptimize's 'Lazy-load images?' option, the w3-total-cache/w3-total-cache.php file to be present on disk with the plugin disabled, a class named MinifyHTML to be loaded into scope by another plugin, and the malicious comment to be approved by a moderator before the payload renders.

The Autoptimize plugin for WordPress is vulnerable to Stored Cross-Site Scripting via REQUESTURI Path in all versions up to, and including, 3.1.15.1 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. Exploitation requires the Critical CSS feature to be active with a valid API key configured, as this is the precondition for unauthenticated frontend requests to trigger queue entries via aoccssenqueue().

The Autoptimize plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the lazy-loading image processing in all versions up to, and including, 3.1.14. This is due to the use of an overly permissive regular expression in the addlazyload function that replaces all occurrences of \ssrc= in image tags without limiting to the actual attribute. 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 by crafting an image tag where the src URL contains a space followed by src=, causing the regex to break the HTML structure and promote text inside attribute values into executable HTML attributes.

The Autoptimize plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the LCP Image to preload metabox in all versions up to, and including, 3.1.13 due to insufficient input sanitization and output escaping on user-supplied image attributes in the "createimgpreloadtag" function. 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.