CVE-2025-58998 is a critical vulnerability found in the s2Member plugin for WordPress, developed by Cristián Lávaque. The issue arises from the unsafe deserialization of untrusted data, which allows attackers to perform object injection attacks. Deserialization vulnerabilities occur when untrusted input is deserialized without proper validation, enabling attackers to inject malicious objects that can execute arbitrary code or manipulate application logic. This vulnerability affects all versions of s2Member up to and including version 250701. The CVSS 3.1 base score of 9.8 reflects the high severity, with an attack vector of network (remote exploitation), no required privileges, no user interaction, and impacts on confidentiality, integrity, and availability. Exploiting this flaw could allow attackers to execute arbitrary code on the server hosting the plugin, potentially leading to full system compromise, data theft, or service disruption. Although no public exploits are currently known, the vulnerability’s characteristics make it highly exploitable. The lack of available patches at the time of disclosure increases the urgency for organizations to implement interim mitigations. The s2Member plugin is widely used for membership management on WordPress sites, often handling sensitive user data and payment information, making this vulnerability particularly dangerous in e-commerce and membership-based websites.

For European organizations, the impact of this vulnerability is significant. Exploitation could lead to unauthorized access to sensitive customer data, including personal and payment information, resulting in data breaches and regulatory non-compliance under GDPR. The integrity of membership and subscription data could be compromised, leading to fraudulent access or manipulation of user privileges. Availability could also be affected if attackers deploy ransomware or disrupt services, causing operational downtime and reputational damage. Organizations relying on s2Member for critical business functions, especially in sectors like e-commerce, education, and online services, face heightened risks. The potential for remote, unauthenticated exploitation increases the threat landscape, necessitating urgent attention to prevent exploitation. Additionally, the breach of such systems could have cascading effects on partner organizations and customers, amplifying the overall impact.

Immediate mitigation steps include monitoring for unusual activity related to s2Member plugin usage and restricting access to the WordPress admin interface and plugin files through network segmentation and firewall rules. Organizations should implement Web Application Firewalls (WAFs) with custom rules to detect and block suspicious deserialization payloads targeting s2Member endpoints. Until an official patch is released, disabling the s2Member plugin or replacing it with alternative membership management solutions can reduce risk. Applying strict input validation and sanitization on all data inputs that interact with the plugin is critical to prevent malicious payloads. Regularly updating WordPress core and all plugins, including s2Member once a patch is available, is essential. Conducting code audits and penetration testing focused on deserialization vulnerabilities can help identify and remediate similar issues proactively. Finally, organizations should prepare incident response plans specific to web application compromises to respond swiftly if exploitation occurs.