CVE-2026-1865: WordPress User Registration SQLi Flaw

CVE-2026-1865 Overview

CVE-2026-1865 is a SQL Injection vulnerability affecting the User Registration & Membership plugin for WordPress. This plugin provides free and paid memberships, subscriptions, content restriction, user profile customization, and custom user registration functionality. The vulnerability exists in all versions up to and including 5.1.2 due to insufficient escaping on user-supplied parameters and lack of sufficient preparation on existing SQL queries.

The flaw allows authenticated attackers with Subscriber-level access and above to inject malicious SQL queries through the membership_ids[] parameter. Successful exploitation enables attackers to append additional SQL queries into already existing queries, which can be used to extract sensitive information from the WordPress database.

Critical Impact

Authenticated attackers with minimal privileges (Subscriber-level) can extract sensitive database information including user credentials, personal information, and other confidential data stored in the WordPress database.

Affected Products

• User Registration & Membership – Free & Paid Memberships, Subscriptions, Content Restriction, User Profile, Custom User Registration & Login Builder plugin for WordPress versions up to and including 5.1.2

Discovery Timeline

• April 8, 2026 - CVE-2026-1865 published to NVD
• April 8, 2026 - Last updated in NVD database

Technical Details for CVE-2026-1865

Vulnerability Analysis

This SQL Injection vulnerability (CWE-89) stems from improper handling of user-supplied input in the membership_ids[] parameter. When users interact with membership-related functionality, the plugin processes this array parameter without adequate sanitization or parameterized query preparation.

The vulnerability is exploitable over the network and requires only basic authentication (Subscriber-level access), which is commonly available on WordPress sites that offer user registration. While the attack complexity is low and requires no user interaction, the impact is focused on confidentiality—attackers can read sensitive database contents but cannot modify data or cause service disruption.

WordPress sites using this plugin for membership management are particularly at risk, as subscriber accounts are often easily obtainable through standard registration processes.

Root Cause

The root cause of this vulnerability is twofold:

1. Insufficient Input Escaping: The membership_ids[] parameter values are not properly escaped before being incorporated into SQL queries, allowing special SQL characters to break out of the intended query context.

2. Lack of Prepared Statements: The existing SQL query does not utilize prepared statements or parameterized queries, which would separate SQL code from user data and prevent injection attacks.

This combination allows attackers to craft malicious input that modifies the logic of database queries, enabling unauthorized data extraction.

Attack Vector

The attack is executed over the network against authenticated WordPress sessions. An attacker must first obtain at least Subscriber-level access to the target WordPress site, which is often achievable through standard user registration if enabled.

Once authenticated, the attacker manipulates the membership_ids[] parameter in requests to the vulnerable plugin functionality. By injecting SQL syntax into this parameter, the attacker can modify the resulting database query to extract data from tables beyond the intended scope.

The vulnerability allows for information extraction attacks, where sensitive data such as user credentials, email addresses, personal information, and other database contents can be retrieved through carefully crafted SQL injection payloads. Since the vulnerability allows appending queries to existing ones, attackers can potentially enumerate entire database tables through iterative extraction techniques.

Detection Methods for CVE-2026-1865

Indicators of Compromise

• Unusual or malformed values in the membership_ids[] parameter containing SQL syntax such as quotes, UNION statements, or comment sequences
• Database query logs showing unexpected queries or UNION-based data extraction attempts
• Abnormal database access patterns from authenticated user sessions
• Error messages in logs indicating SQL syntax errors from the User Registration plugin

Detection Strategies

• Implement Web Application Firewall (WAF) rules to detect SQL injection patterns in the membership_ids[] parameter
• Monitor WordPress debug logs for SQL-related errors originating from the user-registration plugin directory
• Enable database query logging and alert on queries containing suspicious patterns like UNION SELECT, information_schema references, or comment sequences
• Review access logs for repeated requests to membership-related endpoints with varying parameter values

Monitoring Recommendations

• Deploy intrusion detection systems configured to identify SQL injection attack signatures targeting WordPress installations
• Implement real-time alerting for database query anomalies, particularly those involving user data tables
• Monitor authenticated session activity for unusual patterns of requests to membership functionality
• Establish baseline metrics for normal plugin behavior to identify deviations that may indicate exploitation attempts

How to Mitigate CVE-2026-1865

Immediate Actions Required

• Update the User Registration & Membership plugin to a version newer than 5.1.2 immediately
• Review database access logs for signs of exploitation prior to patching
• Audit subscriber-level accounts for suspicious activity or unauthorized registrations
• Consider temporarily disabling the plugin if immediate patching is not possible

Patch Information

The vulnerability has been addressed by the plugin developers. The security fix is documented in the WordPress Changeset Update. Users should update to the latest available version through the WordPress plugin dashboard.

For additional technical details about this vulnerability, refer to the Wordfence Vulnerability Report.

Workarounds

• Implement Web Application Firewall rules to block requests containing SQL injection patterns in the membership_ids[] parameter
• Restrict subscriber-level account registration temporarily until the patch can be applied
• Use database user permissions to limit the WordPress database user's access to only required tables
• Enable WordPress security plugins that provide SQL injection protection at the application layer

# Example: Block suspicious requests at the web server level (Apache)
# Add to .htaccess in WordPress root
<IfModule mod_rewrite.c>
    RewriteEngine On
    RewriteCond %{QUERY_STRING} membership_ids.*(\%27|\'|union|select|concat) [NC]
    RewriteRule .* - [F,L]
</IfModule>