CVE-2025-31612: CBX Poll Object Injection Vulnerability

CVE-2025-31612 Overview

CVE-2025-31612 is a critical PHP Object Injection vulnerability affecting the CBX Poll WordPress plugin developed by Sabuj Kundu. This vulnerability stems from insecure deserialization of untrusted data, allowing attackers to inject malicious serialized PHP objects into the application. When these objects are deserialized, they can trigger arbitrary code execution, data manipulation, or complete site compromise depending on the available gadget chains within the WordPress environment.

Critical Impact

This PHP Object Injection vulnerability allows unauthenticated attackers to inject malicious serialized objects, potentially leading to remote code execution, data theft, or complete WordPress site takeover without any user interaction required.

Affected Products

• CBX Poll WordPress Plugin versions up to and including 1.2.7
• WordPress installations running vulnerable CBX Poll versions
• Any WordPress site with CBX Poll plugin enabled regardless of configuration

Discovery Timeline

• 2025-04-01 - CVE-2025-31612 published to NVD
• 2025-04-02 - Last updated in NVD database

Technical Details for CVE-2025-31612

Vulnerability Analysis

This vulnerability is classified under CWE-502 (Deserialization of Untrusted Data), which occurs when an application deserializes data from an untrusted source without proper validation. In the context of WordPress plugins, PHP Object Injection vulnerabilities arise when user-controllable input is passed to PHP's unserialize() function.

The CBX Poll plugin fails to properly validate or sanitize serialized data before deserializing it. An attacker can craft a malicious serialized PHP object containing a payload that, when processed by the application, executes arbitrary code or performs unauthorized actions. The severity of this vulnerability is compounded by the fact that it requires no authentication and can be exploited remotely over the network without any user interaction.

PHP Object Injection attacks leverage "magic methods" such as __destruct(), __wakeup(), or __toString() that are automatically invoked during the deserialization process. When combined with existing class methods in WordPress core, themes, or other plugins (known as "gadget chains"), attackers can chain these methods together to achieve code execution or other malicious outcomes.

Root Cause

The root cause of this vulnerability is the improper handling of serialized PHP data within the CBX Poll plugin. The application accepts serialized data from untrusted sources and passes it directly to PHP's unserialize() function without implementing proper input validation, sanitization, or using safer alternatives like JSON encoding.

WordPress plugins that store complex data structures often use PHP serialization for convenience. However, when this serialized data can be influenced by user input—whether through form submissions, cookies, database entries, or other vectors—it creates an opportunity for attackers to inject malicious objects. The CBX Poll plugin versions through 1.2.7 do not adequately protect against this attack vector.

Attack Vector

The attack can be executed remotely over the network by any unauthenticated user. The attacker crafts a specially formatted serialized PHP object string containing malicious payload code or references to dangerous class methods. This serialized string is then submitted to the vulnerable endpoint in the CBX Poll plugin.

When the plugin processes the request and deserializes the malicious input, PHP instantiates the attacker-controlled object. If appropriate gadget chains exist within the WordPress installation (from core, themes, or other plugins), the attacker can chain method calls to achieve arbitrary file operations, database manipulation, or remote code execution.

The vulnerability mechanism involves crafting a serialized PHP object payload targeting magic methods that execute during deserialization. When the CBX Poll plugin processes this payload through unserialize(), the malicious object's destructor or wakeup methods can trigger a chain of method calls leading to code execution. For detailed technical analysis, refer to the Patchstack vulnerability report.

Detection Methods for CVE-2025-31612

Indicators of Compromise

• Unusual serialized data patterns in web server access logs, particularly containing PHP class names and object notation (O:, s:, a:)
• Unexpected file creation or modification in WordPress directories following CBX Poll plugin requests
• Web application firewall (WAF) alerts for serialized PHP object patterns in HTTP request parameters
• Anomalous database queries or modifications originating from the CBX Poll plugin context

Detection Strategies

• Deploy web application firewall rules to detect and block serialized PHP object patterns in incoming requests
• Implement file integrity monitoring on WordPress installations to detect unauthorized changes
• Enable verbose logging for the CBX Poll plugin and monitor for deserialization-related errors or warnings
• Use WordPress security plugins that can detect and alert on suspicious plugin behavior

Monitoring Recommendations

• Monitor web server logs for requests to CBX Poll endpoints containing serialized data patterns
• Implement real-time alerting for any new file creation within the WordPress installation directory
• Track and audit database changes, particularly in tables associated with the CBX Poll plugin
• Review PHP error logs for deserialization warnings or object instantiation failures

How to Mitigate CVE-2025-31612

Immediate Actions Required

• Update the CBX Poll plugin to a patched version immediately if one is available from the plugin developer
• If no patch is available, deactivate and remove the CBX Poll plugin until a security update is released
• Conduct a security audit of the WordPress installation to identify any signs of compromise
• Review server access logs for any suspicious activity targeting the CBX Poll plugin endpoints

Patch Information

Organizations should check for updated versions of the CBX Poll plugin through the WordPress plugin repository or the developer's official website. The vulnerability affects all versions from n/a through 1.2.7. Monitor the Patchstack vulnerability database for updates on available patches.

Until an official patch is released, site administrators should consider the workarounds listed below to reduce exposure to this vulnerability.

Workarounds

• Deactivate the CBX Poll plugin entirely until a patched version is available
• Implement WAF rules to block requests containing serialized PHP object patterns targeting the plugin
• Restrict access to the WordPress admin area and plugin endpoints using IP-based access controls
• Consider replacing CBX Poll with an alternative polling plugin that does not have known vulnerabilities

# WordPress CLI command to deactivate CBX Poll plugin
wp plugin deactivate cbxpoll --path=/var/www/html/wordpress

# Verify plugin status
wp plugin status cbxpoll --path=/var/www/html/wordpress