CVE-2024-43242: Ultimate Membership Pro Vulnerability

CVE-2024-43242 Overview

CVE-2024-43242 is a critical PHP Object Injection vulnerability affecting the Ultimate Membership Pro plugin for WordPress developed by wpindeed. This insecure deserialization flaw allows unauthenticated attackers to inject malicious serialized PHP objects, potentially leading to remote code execution, data exfiltration, or complete site compromise. The vulnerability stems from improper handling of untrusted data during deserialization operations within the plugin.

Critical Impact

Unauthenticated attackers can exploit this PHP Object Injection vulnerability to execute arbitrary code on vulnerable WordPress installations, potentially leading to complete server compromise, data theft, or website defacement.

Affected Products

• wpindeed Ultimate Membership Pro versions through 12.7
• WordPress sites running vulnerable versions of the indeed-membership-pro plugin
• All installations where the plugin is active, regardless of configuration

Discovery Timeline

• 2024-08-19 - CVE-2024-43242 published to NVD
• 2026-04-01 - Last updated in NVD database

Technical Details for CVE-2024-43242

Vulnerability Analysis

This vulnerability is classified under CWE-502 (Deserialization of Untrusted Data). The Ultimate Membership Pro plugin fails to properly validate and sanitize serialized data before processing it through PHP's deserialization functions. When an attacker supplies a malicious serialized payload, the application blindly deserializes it, potentially instantiating arbitrary PHP objects with attacker-controlled properties.

The scope of this vulnerability extends beyond the immediate application context, as indicated by the changed scope metric. An attacker exploiting this vulnerability can impact resources beyond the vulnerable component, potentially affecting the underlying server, database, or other applications hosted on the same infrastructure.

Root Cause

The root cause lies in the plugin's acceptance and processing of user-supplied serialized data without proper validation. PHP's unserialize() function, when called on untrusted input, can instantiate any class available in the application's codebase. If a suitable "gadget chain" exists—a sequence of classes with magic methods like __wakeup(), __destruct(), or __toString()—attackers can leverage these to achieve code execution or other malicious outcomes.

Attack Vector

The attack is network-accessible and requires no authentication or user interaction, making it particularly dangerous. Attackers can craft malicious HTTP requests containing serialized PHP objects targeting vulnerable endpoints within the Ultimate Membership Pro plugin.

The exploitation process involves identifying available PHP classes within WordPress core, the vulnerable plugin, or other installed plugins that contain exploitable magic methods. By chaining these classes together in a carefully crafted serialized payload, attackers can trigger arbitrary operations during the deserialization process. Common outcomes include arbitrary file operations, remote code execution, or database manipulation.

For detailed technical information about this vulnerability, refer to the Patchstack Vulnerability Report.

Detection Methods for CVE-2024-43242

Indicators of Compromise

• Unexpected HTTP requests containing base64-encoded or serialized PHP object patterns (e.g., O:, a:, s: prefixes)
• Web server logs showing requests with unusually long query strings or POST bodies containing serialization markers
• Suspicious file creation or modification in the WordPress installation directory
• Unexpected outbound connections from the web server to external hosts
• New or modified PHP files containing obfuscated code or web shells

Detection Strategies

• Deploy Web Application Firewall (WAF) rules to detect and block requests containing PHP serialization patterns in unexpected parameters
• Monitor web server access logs for POST requests to Ultimate Membership Pro endpoints with serialized object signatures
• Implement file integrity monitoring on WordPress core files, plugin directories, and upload folders
• Enable PHP error logging to capture deserialization failures or unexpected class instantiation attempts

Monitoring Recommendations

• Configure real-time alerting for any requests matching PHP object injection signatures targeting the /wp-content/plugins/indeed-membership-pro/ path
• Monitor for process execution by the web server user (www-data, apache, nginx) that deviates from normal patterns
• Track database queries for unexpected operations such as new admin user creation or option value modifications
• Review authentication logs for any suspicious login activity following potential exploitation attempts

How to Mitigate CVE-2024-43242

Immediate Actions Required

• Update Ultimate Membership Pro plugin to a version newer than 12.7 immediately
• If an update is not available, temporarily deactivate the Ultimate Membership Pro plugin until a patch is released
• Conduct a thorough security audit of the WordPress installation to identify any signs of compromise
• Review user accounts for any unauthorized administrative access or newly created accounts
• Scan the file system for any unauthorized modifications or web shells

Patch Information

WordPress site administrators should update to the latest version of Ultimate Membership Pro that addresses this vulnerability. The update should be obtained through the official WordPress plugin repository or directly from the vendor. Before updating, it is recommended to create a full backup of the WordPress installation including the database.

For additional details and patch information, consult the Patchstack Vulnerability Report.

Workarounds

• Implement a WAF rule to block requests containing serialized PHP objects (patterns like O:[0-9]+: or a:[0-9]+:) in all user-controllable input
• Use WordPress security plugins to add additional input validation layers before requests reach the vulnerable plugin
• Restrict access to the WordPress admin area and plugin endpoints by IP address where feasible
• Consider disabling the plugin entirely if it is not critical to site operations until a patched version is available

# Example .htaccess rule to block potential serialization attacks
# Add to WordPress root .htaccess file

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteCond %{QUERY_STRING} (O:|a:|s:)[0-9]+: [NC,OR]
RewriteCond %{REQUEST_BODY} (O:|a:|s:)[0-9]+: [NC]
RewriteRule ^wp-content/plugins/indeed-membership-pro/ - [F,L]
</IfModule>