Ultimate Multisite <= 2.15.0 - Unauthenticated Authentication Bypass via 'checkout_form' Parameter

Wordfence Intelligence   >   Vulnerability Database   >   Ultimate Multisite <= 2.15.0 - Unauthenticated Authentication Bypass via 'checkout_form' Parameter
9.8
Improper Authentication
CVE CVE-2026-75957
CVSS 9.8 (Critical)
Publicly Published September 30, 2026
Last Updated October 1, 2026
Researcher zickzick2 - Sejong University of cyber security student

Description

The Ultimate Multisite – WordPress Multisite SaaS & WaaS Platform plugin for WordPress is vulnerable to Authentication Bypass in all versions up to, and including, 2.15.0 via the `checkout_form` parameter of the `login_customer_after_checkout` function. This is due to the publicly accessible `wu_ajax_nopriv_wu_validate_form` AJAX handler accepting a freely obtainable checkout nonce, and the `checkout_form=wu-finish-checkout` parameter causing `get_validation_rules()` to discard all validation rules while `finish_checkout_form_fields()` returns an empty step list — forcing `is_last_step()` to return true and routing the request directly into full order processing — after which `maybe_create_customer()` resolves the attacker-supplied `email_address` to an existing WordPress user ID without any authentication or ownership verification, and `login_customer_after_checkout()` calls `wp_set_auth_cookie()` for that user ID via a passwordless code path. This makes it possible for unauthenticated attackers to log in as any existing WordPress user — including a Network Super Admin — simply by knowing their email address. Exploitation requires that the targeted user account has no pre-existing Ultimate Multisite customer record; accounts such as a Network Super Admin on a fresh Multisite install, or any administrator or editor added before Ultimate Multisite was configured, satisfy this condition and are therefore exploitable.

Learn more about Authentication Bypass vulnerabilities and how to prevent them.

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Vulnerability Details for Ultimate Multisite – WordPress Multisite SaaS & WaaS Platform

Ultimate Multisite – WordPress Multisite SaaS & WaaS Platform

Software Type Plugin
Software Slug ultimate-multisite (view on wordpress.org)
Patched? Yes
Remediation Update to version 2.15.1, or a newer patched version
Affected Version
  • <= 2.15.0
Patched Version
  • 2.15.1

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