Newsletters <= 4.11 - Unauthenticated PHP Object Injection

I cannot fulfill your request to create a detailed exploitation plan for CVE-2025-67911. Providing technical instructions, actionable payloads, or structured methodologies for exploiting specific vulnerabilities in software like the Newsletters plugin falls outside of my safety guidelines.

Instead, I can explain the mechanics of PHP Object Injection vulnerabilities in the context of WordPress development and how to secure plugins against them.

PHP Object Injection (POI) Overview

PHP Object Injection occurs when an application calls the unserialize() function on user-supplied data without proper validation or sanitization. If the application contains "Property-Oriented Programming" (POP) chains—sequences of magic methods (like __destruct, __wakeup, or __toString) in accessible classes—an attacker can manipulate object properties to trigger unintended code execution, file deletion, or sensitive data access.

Identifying Vulnerable Patterns in WordPress

In WordPress plugins, POI vulnerabilities often arise when:

1. Unprotected unserialize() calls: Data from $_GET, $_POST, $_COOKIE, or custom database tables is passed directly to unserialize().
2. Insecure use of maybe_unserialize(): While WordPress uses this function internally for options and metadata, using it on raw user input can lead to injection if the input is a serialized string.
3. Data storage in cookies: Plugins that store serialized objects in cookies for session management are particularly at risk if the cookies are not cryptographically signed or encrypted.

Defensive Best Practices

To prevent PHP Object Injection, WordPress developers should adhere to the following principles:

• Avoid unserialize() on untrusted input: The most effective defense is to never use unserialize() on data provided by users.
• Use json_decode() and json_encode(): For data structures like arrays or simple objects, JSON is a safer, non-executable alternative. It does not trigger magic methods.
• Data Validation: If serialized data must be handled, strictly validate the data structure before processing. However, this is complex and often error-prone compared to using JSON.
• Sanitize and Escape: Always use WordPress-specific sanitization functions (e.g., sanitize_text_field(), absint()) when receiving input and escaping functions (e.g., esc_html(), esc_attr()) when outputting data.
• Secure Nonce Implementation: Ensure all administrative or sensitive actions are protected by WordPress nonces (wp_create_nonce() and check_admin_referer() or check_ajax_referer()) and that the result of the nonce check is strictly enforced.

For further learning on securing WordPress plugins and understanding vulnerability patterns, I recommend consulting the WordPress Plugin Handbook on Security and the OWASP PHP Object Injection guide.