CVE-2026-16736 in User Registration & Membership Plugin
Summary
by MITRE • 08/05/2026
The User Registration & Membership WordPress plugin before 5.2.6 does not enforce the site's registration-disabled setting when processing registration-form submissions, allowing unauthenticated users to create new accounts even when the administrator has turned off open registration.
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Analysis
by VulDB Data Team • 08/05/2026
The vulnerability in the User Registration & Membership WordPress plugin affects versions prior to 5.2.6 and represents a critical access control flaw that directly undermines the security posture of WordPress installations. This issue stems from a failure in the plugin's validation logic where it does not properly respect the site's registration settings, specifically when the administrator has disabled open user registration through the standard WordPress configuration options. The vulnerability creates an unexpected pathway for unauthorized account creation that bypasses fundamental security controls designed to prevent public registration.
This technical flaw operates at the application level and can be classified as a failure in access control enforcement according to CWE-284. The plugin's registration processing logic does not perform adequate checks against the WordPress core configuration settings that govern who may register for accounts on the site. When administrators disable open registration through the wp-admin interface, this setting should be respected by all plugins that handle user registration functionality. However, the affected plugin version fails to query or validate this critical configuration parameter before proceeding with account creation processes.
The operational impact of this vulnerability is significant as it allows any unauthenticated user to submit registration forms and create new accounts regardless of administrative intentions. This behavior directly violates the principle of least privilege and can lead to several downstream security consequences including unauthorized access to restricted content, potential abuse of site resources, and the creation of spam accounts that could be used for malicious purposes such as comment spam or phishing activities. Attackers can exploit this vulnerability systematically without requiring any authentication credentials, making it particularly dangerous in publicly accessible environments.
From a threat modeling perspective, this vulnerability aligns with ATT&CK technique T1078 which covers legitimate credentials and T1566 which covers credential harvesting through social engineering. The flaw enables adversaries to expand their presence on the target system without requiring prior access or compromising existing user credentials. Security professionals should note that this issue represents a configuration-based access control weakness rather than a traditional authentication bypass, meaning it affects the integrity of the site's registration policies rather than directly compromising authentication mechanisms.
The recommended mitigation strategy involves immediate upgrade to version 5.2.6 or later of the User Registration & Membership plugin where the vulnerability has been addressed through proper validation of the site's registration settings. Administrators should also implement additional monitoring for unexpected user registrations and consider implementing rate limiting on registration attempts to detect potential abuse. Regular security audits should verify that all plugins properly respect WordPress core configuration settings, particularly those related to user management and access control. Organizations using this plugin should conduct thorough vulnerability assessments to identify any other plugins that might exhibit similar behavior in handling user registration processes.