CVE-2026-19423: Ultimate Member WordPress Vulnerability

CVE-2026-19423 Overview

CVE-2026-19423 is a privilege escalation vulnerability in the Ultimate Member WordPress plugin versions prior to 2.13.0. The plugin fails to validate submitted role selections when it cannot resolve the roles permitted by a profile form. Instead of enforcing the form's own allow-list, the plugin checks the submitted value against the site's registered role names. Unauthenticated attackers can register through the plugin's own form and assign themselves arbitrary capabilities, including administrator-equivalent access. The flaw is categorized under CWE-269 Improper Privilege Management.

Critical Impact
Unauthenticated attackers can register accounts with administrator-equivalent capabilities, resulting in full compromise of the WordPress site.

Affected Products

Ultimate Member WordPress plugin versions prior to 2.13.0
WordPress sites running the plugin with public registration forms enabled
Sites with custom role definitions that overlap with the site's registered role names

Discovery Timeline

2026-08-28 - CVE-2026-19423 published to NVD
2026-08-28 - Last updated in NVD database

Technical Details for CVE-2026-19423

Vulnerability Analysis

The Ultimate Member plugin exposes a registration workflow that accepts a role identifier as part of the submitted form data. The plugin attempts to determine which roles a specific profile form permits and, when that resolution fails, falls back to a broader validation step. This fallback compares the submitted role against every role registered on the WordPress site instead of restricting the value to the form's configured allow-list. The result is a broken authorization check that treats any legitimate site role as an acceptable selection during unauthenticated registration.

Root Cause

The root cause is improper privilege management [CWE-269] in the role validation logic. The plugin conflates two distinct trust boundaries: the set of roles a form is authorized to assign, and the set of roles that exist on the WordPress installation. When the form-scoped allow-list cannot be resolved, the code degrades to the site-wide role list, effectively bypassing the intended restriction. Any role name present on the site becomes selectable during registration.

Attack Vector

An unauthenticated attacker submits the plugin's registration form and includes a role parameter referencing a privileged role such as administrator. Because the plugin validates the value against the site's registered roles rather than the form's allow-list, the submission is accepted. The resulting user account is provisioned with the requested capabilities, granting the attacker administrator-equivalent control over the site. The attack requires network access to the registration endpoint and no user interaction.

No verified public proof-of-concept code is available. See the WPScan Vulnerability Detail for additional technical context.

Detection Methods for CVE-2026-19423

Indicators of Compromise

Newly created WordPress user accounts assigned the administrator or other privileged role shortly after registration form submissions.
Unexpected role assignments logged in the wp_usermeta table where meta_key = wp_capabilities references privileged roles.
Registration events originating from public IP addresses immediately followed by administrative actions such as plugin installation or theme editing.
New administrative accounts with email domains inconsistent with existing staff accounts.

Detection Strategies

Audit WordPress user tables for accounts created since the plugin was installed and correlate creation timestamps with registration form POST requests.
Inspect web server access logs for POST requests to Ultimate Member registration endpoints containing role parameters.
Enable and review WordPress activity logs to identify capability changes tied to newly registered users.

Monitoring Recommendations

Alert on any new user account assigned an administrator or editor role that did not originate from an authenticated administrative session.
Monitor plugin installation, theme modification, and file upload activity performed by recently created accounts.
Forward WordPress and web server logs to a centralized logging platform to correlate registration events with follow-on privileged actions.

How to Mitigate CVE-2026-19423

Immediate Actions Required

Update the Ultimate Member plugin to version 2.13.0 or later on all WordPress installations.
Audit all existing user accounts and remove any unauthorized privileged accounts created through the registration form.
Rotate credentials and session tokens for legitimate administrator accounts after remediation.
Review installed plugins, themes, and uploaded files for backdoors or modifications introduced by attacker-created accounts.

Patch Information

The vendor addressed the vulnerability in Ultimate Member 2.13.0 by correcting the role validation logic so submitted role selections are checked against the form's own allow-list rather than the site's registered role names. Refer to the WPScan Vulnerability Detail for advisory details.

Workarounds

Disable public registration in the Ultimate Member plugin settings until the update to 2.13.0 or later is applied.
Restrict access to the registration endpoint at the web server or WAF layer to trusted IP addresses.
Remove or disable custom roles that grant elevated capabilities while the plugin remains unpatched.

bash

# Configuration example: block Ultimate Member registration endpoint at nginx
location ~* /register/ {
    allow 203.0.113.0/24;
    deny all;
}