Description

The Optimole WordPress plugin before 4.2.13 does not escape unrecognized attributes of its video-player block before rendering them onto the block's wrapper element, allowing users with the Author role and above to store an event-handler attribute that executes scripts in the browser of any user, such as an administrator, who views the post.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "6.8",
  "pubDate": "2026-09-26T07:17:03.430Z",
  "pubdate": "2026-09-26T07:17:03.430Z",
  "executiveSummary": "The Optimole WordPress plugin contains a Stored Cross-Site Scripting (XSS) vulnerability due to insufficient input validation and output encoding within its video-player block implementation.\nThis vulnerability allows authenticated users with Author-level privileges or higher to inject malicious JavaScript payloads into post content via unrecognized block attributes.\nThe malicious payload is stored within the WordPress database and subsequently rendered without sanitization on the frontend when the affected post is viewed.\nSuccessful exploitation allows an attacker to execute arbitrary scripts in the browser of any visitor, including high-privileged users like administrators.\nThis facilitates session hijacking, unauthorized administrative actions, or credential theft.\nThe vulnerability affects all versions of the Optimole plugin prior to 4.2.13.\nImmediate remediation involves updating the plugin to version 4.2.13 or later.",
  "technicalDetails": "The vulnerability resides in the way the Optimole plugin's video-player block processes and renders its attributes. Specifically, the block's frontend rendering logic fails to properly sanitize or whitelist attributes before injecting them into the wrapper element of the block.\nBy design, WordPress blocks are parsed into HTML. When an attacker includes an unrecognized attribute within the video-player block's block-editor syntax, the plugin fails to strip or escape this data. An attacker can leverage this oversight to inject event-handler attributes, such as 'onmouseover', 'onerror', or 'onload', into the rendered HTML markup.\nThe exploitation flow begins with an authenticated user (Author level or higher) creating or modifying a post. During the block insertion process, the attacker crafts a malicious payload by adding an arbitrary, non-sanitized attribute to the video-player block structure. For example, an attribute defined as 'data-custom=\"x\" onerror=\"alert(document.cookie)\"' is processed by the plugin's server-side rendering or client-side rendering engine.\nBecause the plugin does not validate these unrecognized attributes against an allowlist, the injected payload is stored directly in the wp_posts table as part of the post_content.\nWhen a victim (e.g., an administrator or an unsuspecting site visitor) loads the page containing the compromised video-player block, the browser renders the malicious attribute as an executable HTML event handler. Upon triggering the specified event—such as the element loading or a hover action—the browser executes the embedded JavaScript within the security context of the victim's session.\nThis leads to a Stored XSS scenario, enabling a broad range of malicious activities including, but not limited to, the exfiltration of sensitive cookies, CSRF attacks performed in the context of the authenticated victim, or forced redirection to external malicious sites.\nThe flaw stems from a lack of secure coding practices regarding dynamic attribute handling. By failing to ensure that only expected attributes are rendered, the plugin allows user-supplied input to alter the DOM structure of the page, bypassing standard security measures.\nAffected versions are strictly limited to those below 4.2.13, which introduced the necessary sanitization routines to filter and escape input attributes during the rendering cycle."
}