CVE-2025-2594: User Registration Auth Bypass Vulnerability

CVE-2025-2594 Overview

The User Registration & Membership WordPress plugin before version 4.1.3 contains an authentication bypass vulnerability that allows attackers to authenticate as any user, including administrators, by simply using the target account's user ID. The vulnerability stems from improper validation of data in an AJAX action when the Membership Addon is enabled.

Critical Impact

Attackers can gain complete administrative access to WordPress installations by exploiting this authentication bypass, potentially leading to full site compromise, data theft, and malicious content injection.

Affected Products

• WPEverest User Registration & Membership (Free) versions prior to 4.1.3
• WPEverest User Registration & Membership (Pro) versions prior to 4.1.3
• WordPress installations with Membership Addon enabled

Discovery Timeline

• 2025-04-22 - CVE CVE-2025-2594 published to NVD
• 2025-09-30 - Last updated in NVD database

Technical Details for CVE-2025-2594

Vulnerability Analysis

This authentication bypass vulnerability allows unauthenticated attackers to impersonate any registered user on a WordPress site, including administrators. The flaw exists in the AJAX action handler used by the Membership Addon functionality. When a user attempts to authenticate, the plugin fails to properly validate the authentication request, allowing an attacker to specify an arbitrary user ID and gain access to that account without providing valid credentials.

The vulnerability is particularly dangerous because it requires no prior authentication and can be exploited remotely over the network. Once an attacker gains administrative access, they have complete control over the WordPress installation, including the ability to install malicious plugins, modify content, access sensitive user data, and potentially pivot to the underlying server infrastructure.

Root Cause

The root cause is improper input validation in an AJAX action handler within the Membership Addon component. The plugin does not adequately verify that the requesting user has legitimate authority to authenticate as the specified user ID. This allows any remote attacker to craft a malicious request that bypasses the normal authentication flow entirely.

Attack Vector

The attack can be executed remotely over the network without any authentication. An attacker simply needs to identify a target WordPress installation running a vulnerable version of the User Registration & Membership plugin with the Membership Addon enabled. By crafting a specially formed AJAX request containing a target user ID (such as the administrator account, typically user ID 1), the attacker can authenticate as that user without knowledge of their password.

The attack is relatively straightforward to execute once the vulnerable endpoint is identified. The attacker submits a malicious AJAX request to the WordPress site specifying the desired user ID, and the vulnerable plugin processes this request without proper validation, granting the attacker an authenticated session as the target user.

Detection Methods for CVE-2025-2594

Indicators of Compromise

• Unexpected administrative login sessions from unfamiliar IP addresses
• AJAX requests to WordPress admin-ajax.php with suspicious user ID parameters
• Multiple authentication events for administrative accounts without corresponding login page activity
• New administrator accounts or modified user permissions without authorized changes

Detection Strategies

• Monitor WordPress admin-ajax.php endpoint for abnormal request patterns, particularly those involving user authentication functions
• Review authentication logs for sessions that bypass normal login workflows
• Implement web application firewall (WAF) rules to detect and block exploitation attempts targeting this AJAX action
• Audit user session creation events and correlate with expected login activity

Monitoring Recommendations

• Enable comprehensive logging on WordPress installations including AJAX request logging
• Monitor for new administrative user accounts or privilege escalation events
• Configure alerts for authentication events originating from unusual geographic locations or IP ranges
• Regularly audit the membership and user registration plugin configurations and access logs

How to Mitigate CVE-2025-2594

Immediate Actions Required

• Update User Registration & Membership plugin to version 4.1.3 or later immediately
• Temporarily disable the Membership Addon if immediate patching is not possible
• Review all administrative accounts for unauthorized access or modifications
• Audit recent authentication logs for signs of exploitation
• Consider temporarily restricting access to admin-ajax.php for unauthenticated users if feasible

Patch Information

WPEverest has released version 4.1.3 of the User Registration & Membership plugin which addresses this authentication bypass vulnerability. Site administrators should update to this version or later through the WordPress plugin update mechanism. For detailed information about the vulnerability, refer to the WPScan Vulnerability Report.

Workarounds

• Disable the Membership Addon until the patch can be applied
• Implement IP-based access controls for WordPress administrative functions
• Deploy a web application firewall with rules to block suspicious AJAX authentication requests
• Consider temporarily deactivating the User Registration & Membership plugin if the Membership Addon cannot be disabled independently

# Configuration example - Restrict admin-ajax.php access (Apache .htaccess)
# Note: This may impact legitimate plugin functionality
<Files admin-ajax.php>
    Order deny,allow
    Deny from all
    # Allow known safe IP addresses
    Allow from 192.168.1.0/24
</Files>