Autoptimize < 3.1.15 - Contributor+ Stored XSS via Lazy-loaded Image Attributes

Description

The plugin is vulnerable to Stored Cross-Site Scripting via the lazy-loading image processing due to the use of an overly permissive regular expression in the `add_lazyload` 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.