CVE-2025-3439 is a critical security vulnerability identified in the Everest Forms – Contact Form, Quiz, Survey, Newsletter & Payment Form Builder plugin for WordPress, affecting all versions up to and including 3.1.1. The flaw is a PHP Object Injection vulnerability caused by unsafe deserialization of untrusted data from the 'field_value' parameter. Deserialization vulnerabilities occur when untrusted input is converted back into objects without proper validation, enabling attackers to craft malicious serialized objects that, when deserialized, can manipulate application logic or execute arbitrary code. In this case, unauthenticated attackers can send specially crafted requests to inject PHP objects. However, the vulnerability alone does not guarantee exploitation because no gadget POP (Property Oriented Programming) chain exists within Everest Forms itself. A POP chain is a sequence of existing code snippets (gadgets) that attackers leverage to perform malicious actions during deserialization. If the target WordPress site has other plugins or themes installed that contain such POP chains, the attacker can chain these with the injection to execute harmful actions such as deleting arbitrary files, retrieving sensitive data, or executing arbitrary code. The vulnerability has a CVSS 3.1 base score of 9.8, indicating critical severity with network attack vector, no required privileges or user interaction, and high impact on confidentiality, integrity, and availability. Although no known exploits are currently reported in the wild, the potential impact is severe, especially on sites with multiple plugins or themes that may provide the necessary POP chains for exploitation.

The impact of CVE-2025-3439 is potentially severe for organizations running WordPress sites with the Everest Forms plugin, especially if other plugins or themes containing gadget POP chains are installed. Exploitation can lead to full system compromise, including arbitrary code execution, data theft, and destruction of files. This can result in loss of sensitive customer data, defacement, ransomware deployment, or use of the compromised site as a pivot point for further attacks within an organization’s network. Since the vulnerability requires no authentication or user interaction, it can be exploited remotely by any attacker scanning for vulnerable sites. The wide usage of WordPress and the popularity of form builder plugins increase the attack surface. Organizations relying on Everest Forms for customer interaction, surveys, or payment processing face risks to business continuity, reputation, and regulatory compliance if exploited.

1. Immediate upgrade: Organizations should update Everest Forms to a patched version once released by the vendor. Until then, consider disabling or removing the plugin if feasible. 2. Plugin and theme audit: Conduct a thorough audit of all installed plugins and themes to identify those containing known POP chains or unsafe deserialization patterns. Remove or update such components to reduce exploitation risk. 3. Web Application Firewall (WAF): Deploy and configure a WAF with rules to detect and block malicious serialized payloads targeting the 'field_value' parameter or suspicious POST requests to Everest Forms endpoints. 4. Input validation and sanitization: Implement additional input validation layers at the application or server level to reject unexpected serialized input. 5. Principle of least privilege: Restrict file system and database permissions for the WordPress environment to limit damage if code execution occurs. 6. Monitoring and logging: Enable detailed logging of web requests and monitor for anomalous activity indicative of exploitation attempts. 7. Backup and recovery: Maintain regular, tested backups of WordPress sites and databases to enable rapid recovery if compromise occurs. 8. Network segmentation: Isolate WordPress servers from critical internal systems to limit lateral movement in case of breach.