CVE-2025-52733

Executive Summary

CVE-2025-52733 is a DOM-Based Cross-Site Scripting (XSS) vulnerability discovered in the ANON::form embedded secure form plugin (version 1.7 and earlier) by Anonform AB. This vulnerability allows an attacker to inject malicious scripts into the DOM of a web page, which are then executed in the victim's browser. The attack vector is network-based, requires user interaction (e.g., clicking a crafted link), and can lead to data theft, session hijacking, or defacement. The vendor has not released a patch, and no public exploit code is available at this time.

Supply Chain & Package Security

This vulnerability affects a WordPress plugin ecosystem component. The plugin is distributed via the WordPress plugin repository and potentially through third-party marketplaces. Users should verify the integrity of their plugin files and monitor for updates from the vendor.

CVSS Breakdown & Threat Level

• CVSS Score: 6.5 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:L
• Attack Vector (AV): Network (N) – Exploitable remotely.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): Required (R) – Victim must click a malicious link or visit a crafted page.
• Scope (S): Changed (C) – Impact extends beyond the vulnerable component.
• Confidentiality (C): Low (L) – Limited data exposure.
• Integrity (I): Low (L) – Limited ability to modify data.
• Availability (A): Low (L) – Limited impact on availability.

Threat Level: Medium. While the CVSS score is moderate, the lack of a patch and the potential for DOM-based attacks in a widely used form plugin elevate the risk for unpatched installations.

Deep Dive & Mechanics

The vulnerability resides in the ANON::form embedded secure form plugin, which generates secure forms for embedding in web pages. The plugin fails to properly neutralize user-controlled input during web page generation, specifically within the Document Object Model (DOM). This allows an attacker to inject arbitrary JavaScript code that is executed in the context of the victim's browser.

Root Cause: The plugin likely uses innerHTML, document.write, or similar DOM manipulation methods without sanitizing input from URL parameters, form fields, or other user-controllable sources. For example, a parameter like ?form_id=<script>alert(1)</script> might be directly injected into the DOM.

Attack Flow:

1. Attacker crafts a malicious URL containing a JavaScript payload in a vulnerable parameter.
2. Victim clicks the link or visits a page hosting the vulnerable plugin.
3. The plugin processes the input and injects it into the DOM without sanitization.
4. The injected script executes in the victim's browser, allowing the attacker to steal cookies, redirect to phishing sites, or perform other malicious actions.

Vulnerable vs. Patched Code

Since no patch is available, we can only infer the vulnerable code pattern. The following example demonstrates a typical DOM-based XSS vulnerability:

Vulnerable Code (JavaScript):

// Vulnerable: Directly sets innerHTML from URL parameter
var formId = new URLSearchParams(window.location.search).get('form_id');
document.getElementById('form-container').innerHTML = '<div>' + formId + '</div>';

Patched Code (Hypothetical):

// Patched: Uses textContent or sanitizes input
var formId = new URLSearchParams(window.location.search).get('form_id');
var sanitized = DOMPurify.sanitize(formId);
document.getElementById('form-container').textContent = sanitized;

The patched version would use textContent instead of innerHTML or employ a sanitization library like DOMPurify to strip malicious code.

Exploitation & Lab Setup

Red Team (Attack Simulation)

Prerequisites:

• A WordPress instance with ANON::form embedded secure form plugin version 1.7 installed.
• A victim user who will click a crafted link.

Exploitation Steps:

1. Identify a vulnerable parameter (e.g., form_id, redirect_url, or callback).
2. Craft a malicious URL:

   http://target-site.com/?form_id=<img src=x onerror=alert('XSS')>
   

3. Send the link to the victim via email, social engineering, or other means.
4. When the victim clicks the link, the script executes in their browser.

Proof-of-Concept (PoC) Code:

<!-- PoC: Save as poc.html and open in browser -->
<!DOCTYPE html>
<html>
<head><title>PoC for CVE-2025-52733</title></head>
<body>
<h1>DOM-Based XSS PoC</h1>
<p>Click the link below to trigger the vulnerability:</p>
<a href="http://target-site.com/?form_id=<script>alert('XSS')</script>">Click Me</a>
</body>
</html>

Blue Team (Defense & Detection)

Detection Steps:

1. Monitor web server logs for suspicious URL parameters containing <script>, <img onerror>, or other XSS payloads.
2. Use browser-based security headers (e.g., Content-Security-Policy) to mitigate impact.
3. Implement input validation and output encoding in the plugin code.

Mitigation Lab Setup:

• Deploy a WAF (e.g., ModSecurity) with rules to block common XSS patterns.
• Use a browser extension like NoScript to prevent script execution.

Indicators of Compromise (IOCs)

• Network IOCs:
  • URLs containing ?form_id= followed by JavaScript code (e.g., <script>, <img onerror>).
  • HTTP requests with unusual query parameters or encoded payloads.
• Host IOCs:
  • Presence of unexpected JavaScript files in the web root.
  • Modified plugin files (e.g., anonform-embedded-secure-form.php).
• Behavioral IOCs:
  • Unusual outbound connections from the web server.
  • Unexpected DOM modifications in the browser (e.g., injected iframes or scripts).

Detection Engineering

YARA Rule

rule CVE_2025_52733_DOM_XSS {
    meta:
        description = "Detects DOM-based XSS patterns in ANON::form plugin"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-52733"
    strings:
        $xss1 = /form_id=[^&]*<script/i
        $xss2 = /form_id=[^&]*<img[^>]+onerror/i
        $xss3 = /form_id=[^&]*onload/i
    condition:
        any of them
}

Sigma Rule

title: CVE-2025-52733 DOM-Based XSS in ANON::form Plugin
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects HTTP requests with XSS payloads targeting the ANON::form plugin
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        c-uri|contains:
            - 'form_id=<script'
            - 'form_id=<img'
            - 'form_id=javascript:'
    condition: selection
falsepositives:
    - Legitimate use of form_id parameter with safe values
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-52733 DOM-Based XSS Attempt"; flow:to_server,established; content:"form_id"; http_uri; pcre:"/form_id=[^&]*(<script|<img[^>]+onerror|onload)/i"; classtype:web-application-attack; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin until a patch is available.
2. Implement a Web Application Firewall (WAF) with rules to block XSS payloads.
3. Use Content Security Policy (CSP) headers to restrict script execution:

   Content-Security-Policy: default-src 'self'; script-src 'self' 'unsafe-inline' 'unsafe-eval'; 
   

   (Note: unsafe-inline may be needed for legitimate plugin functionality, but should be avoided if possible.)

Long-Term Fixes:

• The vendor should release a patched version that sanitizes all user inputs before DOM insertion.
• Developers should use safe DOM methods like textContent or sanitization libraries (e.g., DOMPurify).
• Conduct regular security audits and penetration testing.

Workarounds:

• If the plugin is critical, consider using a different form plugin that is actively maintained.
• Monitor the vendor's website for updates.

Valters IT
Securing Digital Frontiers