CVE-2026-6247: Scratchblocks for WP XSS Vulnerability

CVE-2026-6247 Overview

CVE-2026-6247 is a Stored Cross-Site Scripting (XSS) vulnerability in the scratchblocks for WP plugin for WordPress. The flaw affects all versions up to and including 1.0.1. The vulnerability resides in the element attribute of the scratchblocks shortcode, which lacks proper input sanitization and output escaping. Authenticated users with contributor-level access or higher can inject arbitrary JavaScript that executes in the browsers of visitors viewing affected pages. The issue is tracked under CWE-79: Improper Neutralization of Input During Web Page Generation.

Critical Impact

Authenticated contributors can inject persistent JavaScript that executes against any visitor, enabling session theft, administrative account takeover, and content tampering.

Affected Products

• scratchblocks for WP plugin for WordPress (all versions ≤ 1.0.1)
• WordPress sites permitting contributor-level user registration
• WordPress installations exposing the scratchblocks shortcode to non-administrative roles

Discovery Timeline

• 2026-05-12 - CVE-2026-6247 published to NVD
• 2026-05-12 - Last updated in NVD database

Technical Details for CVE-2026-6247

Vulnerability Analysis

The scratchblocks for WP plugin registers a scratchblocks shortcode that renders Scratch-style code blocks inside WordPress posts and pages. The shortcode accepts an element attribute that is passed through to the rendered HTML output without sufficient sanitization or escaping. Because WordPress contributors are permitted to author posts containing shortcodes, an attacker holding a contributor account can craft shortcode markup that injects arbitrary script content into the page DOM.

The payload is stored persistently in post content. Each time an administrator, editor, or site visitor loads the affected post, the injected script runs in their browser session. This enables cookie theft for users without HttpOnly session protection, forced administrative actions via authenticated requests, redirection to attacker-controlled infrastructure, and silent modification of page content.

Root Cause

The root cause is missing input sanitization and missing output escaping on the user-supplied element shortcode attribute. The plugin source at scratchblocks-for-wp.php line 57 emits the attribute value directly into HTML output without calling WordPress escaping primitives such as esc_attr() or esc_html(). Reference the WordPress Plugin Source Code for the vulnerable code path.

Attack Vector

Exploitation requires an authenticated contributor account on the target WordPress site. The attacker creates or edits a post containing a malicious scratchblocks shortcode where the element attribute carries a script payload. Once an editor or administrator previews or publishes the post, or once any visitor loads the page, the injected script executes in the victim's browser with full access to the WordPress session context. See the Wordfence Vulnerability Analysis for additional technical context.

Detection Methods for CVE-2026-6247

Indicators of Compromise

• Posts or pages containing [scratchblocks element="..."] shortcodes with <script>, onerror, onload, or javascript: strings in the attribute value
• Unexpected outbound requests from administrator browser sessions to unfamiliar domains following post previews
• New or modified WordPress administrator accounts created shortly after a contributor submitted content
• HTML-encoded or base64-encoded payloads embedded in wp_posts.post_content referencing the scratchblocks shortcode

Detection Strategies

• Query the wp_posts table for post_content rows containing the scratchblocks shortcode and inspect element attribute values for script syntax
• Review web server access logs for contributor accounts submitting post revisions with suspicious shortcode payloads
• Monitor browser-side Content Security Policy (CSP) violation reports for inline script execution on post pages
• Audit WordPress plugin inventories against the affected version range (≤ 1.0.1)

Monitoring Recommendations

• Alert on creation or modification of WordPress users with administrator or editor roles following contributor post submissions
• Track shortcode usage patterns and flag attribute values exceeding expected length or containing HTML control characters
• Forward WordPress audit logs to a centralized logging platform for retention and correlation
• Monitor for unauthorized changes to wp_options entries such as siteurl, home, and active_plugins

How to Mitigate CVE-2026-6247

Immediate Actions Required

• Update the scratchblocks for WP plugin to a version newer than 1.0.1 once the vendor releases a patched release
• Audit all existing posts and pages for malicious scratchblocks shortcode usage and remove or sanitize affected content
• Review contributor-level and higher user accounts for unauthorized or dormant entries and remove untrusted accounts
• Rotate session cookies and authentication keys defined in wp-config.php if exploitation is suspected

Patch Information

At the time of NVD publication on 2026-05-12, all versions up to and including 1.0.1 are affected. Consult the Wordfence Vulnerability Analysis and the WordPress Plugin Development Reference for the latest release status and remediation guidance.

Workarounds

• Deactivate the scratchblocks for WP plugin until a patched version is available
• Restrict contributor and author capabilities so that untrusted users cannot publish or preview posts containing shortcodes
• Deploy a web application firewall (WAF) rule that blocks scratchblocks shortcode submissions containing <, >, ", or javascript: tokens in the element attribute
• Enforce a strict Content Security Policy that disallows inline scripts on post rendering endpoints

# Disable the vulnerable plugin via WP-CLI until a fix is released
wp plugin deactivate scratchblocks-for-wp
wp plugin status scratchblocks-for-wp

# Search post content for suspicious shortcode usage
wp db query "SELECT ID, post_title FROM wp_posts WHERE post_content LIKE '%[scratchblocks%' AND (post_content LIKE '%<script%' OR post_content LIKE '%onerror=%' OR post_content LIKE '%javascript:%');"