Description

The EWWW Image Optimizer plugin for WordPress is vulnerable to Stored Cross-Site Scripting via 'data-script' Lazy Load Attribute in Post Content in all versions up to, and including, 8.7.3 due to insufficient input sanitization and output escaping. 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. The exploit is achieved by embedding a crafted img element with class='lazyload' and a data-script attribute pointing to an attacker-controlled URL in post content, which the plugin's bundled lazysizes ls.unveilhooks addon then uses to dynamically create and insert a script element into the DOM at page view time.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "6.4",
  "pubDate": "2026-08-19T07:16:27.530Z",
  "pubdate": "2026-08-19T07:16:27.530Z",
  "executiveSummary": "The EWWW Image Optimizer plugin for WordPress, in all versions up to and including 8.7.3, is susceptible to a Stored Cross-Site Scripting (XSS) vulnerability. This security defect arises due to insufficient input sanitization and output escaping applied to user-supplied attributes within post content. Specifically, the vulnerability resides in the handling of the 'data-script' lazy load attribute.\nAuthenticated attackers possessing contributor-level access and above can exploit this flaw by injecting arbitrary web scripts into pages. When an end user accesses a compromised page, the injected payload executes within the context of their browser session. Depending on the privileges of the victim, this can lead to session hijacking, defacement, or further unauthorized interactions within the WordPress environment.\nSuccessful exploitation requires authenticated access with a minimum privilege level of contributor, limiting unauthenticated exploitation vectors. The risk implications are moderate to high, as it allows internal privilege leverage via social engineering or administrative interaction with the injected content.",
  "technicalDetails": "The root cause of the vulnerability is the lack of proper input sanitization and output escaping on attributes processed by the EWWW Image Optimizer plugin. Specifically, the plugin incorporates the bundled lazysizes ls.unveilhooks addon, which is designed to handle lazy loading mechanics for images and media.\nExploitation is achieved by embedding a crafted img element within post content. This malicious img element must include class='lazyload' alongside a 'data-script' attribute pointing to an attacker-controlled URL. During page rendering, the lazysizes ls.unveilhooks addon parses these attributes and dynamically creates and inserts a script element into the Document Object Model (DOM) at page view time.\nThe vulnerable component is the lazy load mechanism processing the 'data-script' Lazy Load Attribute in Post Content. Affected versions include all iterations up to and including 8.7.3.\nThe attack flow proceeds as follows: First, an authenticated attacker with contributor-level privileges or higher creates or edits a post or page containing the malicious img element with the 'data-script' attribute. Second, the post content is saved to the WordPress database without adequate sanitization. Third, when an unsuspecting user requests the affected page, the server renders the post content containing the lazy load attributes. Fourth, the bundled lazysizes ls.unveilhooks addon processes the 'data-script' attribute, dynamically generating and injecting a malicious script element into the DOM. Finally, the injected script executes in the victim's browser, enabling arbitrary script execution within the application's origin.\nAuthentication and privilege requirements mandate that the attacker must have at least contributor-level access to inject post content. Network exposure is standard web-based via HTTP/HTTPS when users visit the rendered pages containing the payload."
}