The vulnerability identified as CVE-2025-13540 affects the Tiare Membership plugin for WordPress, developed by Qode Interactive. This plugin facilitates membership management on WordPress sites. The root cause is improper privilege management (CWE-269) in the 'tiare_membership_init_rest_api_register' function, which handles user registration via the REST API. Specifically, this function does not validate or restrict the user role parameter supplied during registration. As a result, an unauthenticated attacker can craft a registration request specifying the 'administrator' role, thereby gaining full administrative privileges on the WordPress site. This bypasses all normal authentication and authorization controls. The vulnerability affects all plugin versions up to and including 1.2, with no patch currently available. The CVSS v3.1 score is 9.8 (critical), reflecting the vulnerability's ease of exploitation (network attack vector, no privileges or user interaction required) and its severe impact on confidentiality, integrity, and availability. Successful exploitation allows an attacker to fully control the WordPress site, including installing malicious plugins, modifying content, stealing sensitive data, or disrupting site operations. Although no known exploits have been observed in the wild yet, the vulnerability's nature and severity make it a prime target for attackers. The vulnerability is particularly dangerous because WordPress is widely used across Europe for business, government, and personal websites, and membership plugins are common for managing user access. The lack of role validation in the REST API registration endpoint represents a critical security oversight that must be addressed promptly.

For European organizations, this vulnerability poses a severe risk of complete site compromise. Attackers gaining administrator access can exfiltrate sensitive data, deface websites, deploy malware, or use compromised sites as pivot points for further attacks within corporate networks. Organizations relying on WordPress for customer portals, membership sites, or internal collaboration platforms are especially vulnerable. The breach of confidentiality can lead to data protection violations under GDPR, resulting in legal penalties and reputational damage. Integrity loss can disrupt business operations and trustworthiness of published content. Availability impacts may arise from site defacement or denial-of-service conditions caused by malicious administrative actions. The ease of exploitation without authentication or user interaction means attacks can be automated and widespread, increasing the likelihood of rapid compromise. European sectors such as finance, healthcare, education, and government, which often use WordPress for public-facing services, face heightened risks. Additionally, the vulnerability could be leveraged in supply chain attacks if compromised sites serve as distribution points for malware or phishing campaigns targeting European users.

Immediate mitigation steps include disabling the Tiare Membership plugin until a secure patch is released by Qode Interactive. If disabling is not feasible, restrict access to the REST API registration endpoint via web application firewalls (WAFs) or server-level access controls to prevent unauthenticated registration requests. Implement strict input validation and role assignment policies by customizing or overriding the plugin's registration logic to enforce allowed roles only. Monitor WordPress user accounts for suspicious administrator account creations and audit logs for unusual activity. Employ multi-factor authentication (MFA) for all administrator accounts to reduce the impact of compromised credentials. Keep WordPress core, themes, and other plugins up to date to minimize attack surface. Network segmentation can limit attacker lateral movement if a site is compromised. Finally, organizations should prepare incident response plans specific to WordPress compromises and conduct regular security assessments of their web infrastructure.