Detection Guidance

This vulnerability involves a crafted <video> tag with a src attribute containing an embedded class=" substring that exploits a regex bug in the a3 Lazy Load plugin for WordPress. Detection would involve inspecting posts or content for suspicious <video> tags with unusual attribute patterns that break HTML quoting.

Since the vulnerability requires authenticated Contributor-level access to insert the malicious content, detection can include scanning the WordPress database or post content for <video> tags with suspicious src attributes containing class=" substrings or other irregularities.

No specific commands or automated detection tools are provided in the available resources.

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Mitigation Strategies

Immediate mitigation steps include updating the a3 Lazy Load plugin to a version later than 2.7.6 where this vulnerability is fixed.

If an update is not immediately possible, restrict Contributor-level user permissions to prevent insertion of crafted <video> tags.

Additionally, review and sanitize any existing post content for malicious <video> tags that exploit this vulnerability.

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Executive Summary

The a3 Lazy Load plugin for WordPress has a Stored Cross-Site Scripting (XSS) vulnerability in all versions up to and including 2.7.6. This vulnerability arises from a regex bug in the _filter_videos() method that improperly handles HTML attribute quoting when processing crafted <video> elements. An authenticated attacker with Contributor-level access can insert a specially crafted <video> tag with a src attribute containing an embedded class=" substring. This tricks the plugin's class-replacement regex into consuming the attribute-value closing quote, which shifts the HTML5 parser's quote boundary. As a result, attacker-controlled text is promoted from inside a quoted attribute value into standalone event-handler attributes like autofocus or onfocus. The injected script then executes in the browser of any user, including administrators, who views the affected post.

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Impact Analysis

This vulnerability allows an authenticated attacker with Contributor-level access to inject malicious scripts into posts via crafted <video> tags. When other users, including administrators, view these posts, the malicious scripts execute in their browsers. This can lead to unauthorized actions such as session hijacking, defacement, or other malicious activities performed in the context of the victim's browser session.

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