CVE-2025-58998 is a critical security vulnerability classified as a deserialization of untrusted data issue in the s2Member plugin for WordPress, developed by Cristián Lávaque. The vulnerability arises from the plugin's unsafe handling of serialized data inputs, which allows an attacker to inject malicious objects during the deserialization process. This object injection can lead to remote code execution, privilege escalation, or complete system compromise. The vulnerability affects all versions of s2Member up to and including version 250701. The CVSS v3.1 base score is 9.8, reflecting the vulnerability's high impact and ease of exploitation: it requires no privileges, no user interaction, and can be exploited remotely over the network. The flaw compromises confidentiality, integrity, and availability of affected systems. Although no public exploits have been reported yet, the nature of the vulnerability and the widespread use of s2Member in membership and subscription management make it a high-risk target. The vulnerability was reserved in early September 2025 and published in November 2025, indicating recent discovery and disclosure. No official patches or mitigations are currently linked, emphasizing the need for vigilance and proactive defense measures.

European organizations using s2Member for managing memberships, subscriptions, or access control on WordPress sites face severe risks. Exploitation can lead to unauthorized access to sensitive customer data, manipulation or deletion of membership records, and potential full takeover of the web server hosting the plugin. This can result in data breaches violating GDPR regulations, financial losses due to service disruption, reputational damage, and legal consequences. E-commerce platforms and membership-based services are particularly vulnerable, as attackers could manipulate user privileges or inject malicious payloads affecting downstream systems. The critical severity and remote exploitation capability mean that even organizations with limited security monitoring could be compromised rapidly. The lack of known exploits in the wild currently provides a narrow window for mitigation before attackers potentially develop and deploy weaponized exploits.

1. Monitor official s2Member and Cristián Lávaque channels for security patches and apply updates immediately upon release. 2. Until patches are available, implement strict input validation and sanitization on all data inputs that may be deserialized by s2Member. 3. Employ Web Application Firewalls (WAFs) with custom rules to detect and block suspicious serialized payloads or object injection patterns targeting s2Member endpoints. 4. Restrict network access to administrative and plugin-related endpoints to trusted IPs where feasible. 5. Conduct thorough code reviews and security audits of any customizations or integrations involving s2Member deserialization logic. 6. Implement robust logging and monitoring to detect anomalous behavior indicative of exploitation attempts. 7. Educate site administrators on the risks of deserialization vulnerabilities and the importance of timely patching. 8. Consider temporary disabling or replacing s2Member with alternative membership management solutions if patching is delayed.