Stored XSS in a3 Lazy Load WordPress Plugin Allows Script Injection

Executive Summary

The a3 Lazy Load plugin for WordPress has a Stored Cross-Site Scripting (XSS) vulnerability in all versions up to and including 2.7.5. This occurs because the plugin does not properly sanitize or escape user-supplied attributes. As a result, authenticated users with contributor-level access or higher can inject malicious scripts into pages, which will execute whenever any user views those pages.

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Detection Guidance

To detect this vulnerability on your system, you can check if the a3 Lazy Load plugin version is 2.7.5 or earlier, as these versions are vulnerable. You can also scan your WordPress site for pages containing injected scripts in image, iframe, video, source, or embed tags with suspicious attributes like malformed data-src or data-srcset attributes. A practical approach is to search the plugin version via WP-CLI with the command: `wp plugin get a3-lazy-load --field=version`. Additionally, you can grep your WordPress content files or database for suspicious script tags or unusual HTML attributes in media elements. For example, use commands like `grep -r --include=*.php '<script' wp-content/uploads/` or query the database for suspicious content. Monitoring HTTP traffic for unexpected script injections in pages served by the plugin can also help detect exploitation attempts. [1, 2]

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Mitigation Strategies

The immediate step to mitigate this vulnerability is to upgrade the a3 Lazy Load plugin to version 2.7.6 or later, which includes a security hardening patch that fixes the HTML attribute injection flaw. This update improves input sanitization and output escaping for user-supplied attributes in media tags, preventing malicious script injection. Additionally, review and restrict contributor-level access to trusted users only, as the vulnerability requires authenticated contributor-level access or higher to exploit. Consider temporarily disabling the plugin if an immediate upgrade is not possible, and monitor your site for suspicious activity. [1, 2]

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Impact Analysis

This vulnerability can allow attackers with contributor-level access to inject malicious scripts into web pages. These scripts can execute in the browsers of users who visit the affected pages, potentially leading to theft of user data, session hijacking, defacement, or other malicious actions. It compromises the integrity and security of the website and its users.

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