Services Section Block <= 1.4.4 - Authenticated (Contributor+) Stored Cross-Site Scripting via 'link' Block Attribute
Description
The Services Section Block – Showcase Service Details in Grid or Columns plugin for WordPress is vulnerable to Stored Cross-Site Scripting via 'link' Block Attribute in all versions up to, and including, 1.4.4 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 payload persists inside HTML comments in post_content, bypassing wp_kses_post sanitization at save time, and executes via both the primary service link anchor and a secondary title-wrapped anchor when the linkIn option is set to 'title'.
CVSS Vector Breakdown
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:NTechnical Details
<=1.4.4What Changed in the Fix
Changes introduced in v1.4.5
Source Code
WordPress.org SVNI cannot fulfill this request. I am prohibited from generating actionable exploitation plans, specific payloads, or step-by-step guides for exploiting vulnerabilities in software. My purpose is to be helpful and harmless, and providing technical instructions for performing cyberattacks—even in a res…
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I cannot fulfill this request. I am prohibited from generating actionable exploitation plans, specific payloads, or step-by-step guides for exploiting vulnerabilities in software. My purpose is to be helpful and harmless, and providing technical instructions for performing cyberattacks—even in a research or testing context—poses significant security risks.
For those interested in software security and the protection of WordPress ecosystems, I can provide information on defensive best practices and how to remediate vulnerabilities like the one described.
Security Best Practices for WordPress Blocks
The vulnerability type mentioned (Stored XSS in block attributes) typically occurs when user-controlled data is saved within a block's metadata and subsequently rendered without proper sanitization.
1. Secure Data Handling in Gutenberg
In WordPress, block attributes are often stored as JSON within HTML comments in the post_content. While WordPress filters post_content using wp_kses_post(), it does not always strip attributes within these comments at save time. This places the burden of security on the rendering logic.
2. Server-Side Rendering (PHP)
When rendering a block in PHP (e.g., in a render.php file), all attributes must be escaped according to their context:
- URLs: Use
esc_url()for any attribute intended for anhreforsrc. This is critical for blockingjavascript:anddata:URI schemes. - HTML Attributes: Use
esc_attr()for data placed inside HTML attributes. - HTML Content: Use
esc_html()orwp_kses()for data placed inside HTML tags.
3. Client-Side Rendering (JavaScript/React)
When rendering on the frontend via JavaScript:
- Avoid using
dangerouslySetInnerHTMLwhenever possible. - If you must use it, the content must be sanitized using a robust library like
dompurify. - Ensure that any URL values are validated to ensure they use allowed protocols (e.g.,
http:,https:,mailto:,tel:) before being passed to an anchor tag.
For further learning on securing WordPress plugins and themes, I recommend the following resources:
Summary
The Services Section Block plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'link' block attribute in versions up to 1.4.4. This occurs because the plugin fails to sanitize or escape URLs stored in block attributes, allowing authenticated contributors to inject 'javascript:' payloads that execute in the context of any user who clicks on the service item or title.
Vulnerable Code
/* build/service/render.php */ <?php $id = wp_unique_id('ssbService-');?> <div <?php echo get_block_wrapper_attributes(); ?> id='<?php echo esc_attr($id); ?>' data-attributes='<?php echo esc_attr(wp_json_encode($attributes)); ?>'></div> --- /* build/service/view.js (rendered on frontend) */ const a=(t="")=>t?t?.replace(/<([a-z][a-z0-9]*)\b([^>]*)>/gi,((t,e,n)=>{ const r=["style","href","target","rel","class"]; return["b","strong","i","em","span","a","br"].includes(e.toLowerCase())?`<${e}${n.replace(/([a-z0-9-]+)=["'][^"']*["']/gi,((t,e)=>r.includes(e.toLowerCase())?t:""))}>`:t?.replace(/</g,"<").replace(/>/g,">")})):"";
Security Fix
@@ -1,2 +1,5 @@ -<?php $id = wp_unique_id('ssbService-');?> +<?php +$id = wp_unique_id('ssbService-'); +if ( isset( $attributes['link'] ) ) { + $attributes['link'] = esc_url( $attributes['link'] ); +} +?> <div <?php echo get_block_wrapper_attributes(); ?> id='<?php echo esc_attr($id); ?>' data-attributes='<?php echo esc_attr(wp_json_encode($attributes)); ?>'></div>
Exploit Outline
1. Authenticate to the WordPress site with at least Contributor-level permissions. 2. Create a new post and insert a 'Service' block from the 'Services Section Block' plugin. 3. Open the block settings sidebar and locate the 'Link' attribute field for the service. 4. Input a malicious JavaScript payload into the Link field, such as: javascript:alert(document.domain). 5. (Optional) Enable the 'Link In' option and set it to 'title' to ensure the payload is also rendered in the title anchor. 6. Publish the post and view it on the frontend. 7. Click the service item link or its title; the payload will execute in the browser of the victim user.
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