CVE-2026-75957: Ultimate Multisite <= 2.15.0 - Unauthenticated Authentication Bypass via 'checkout_form' Parameter
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 checkoutform parameter of the logincustomeraftercheckout function. This is due to the publicly accessible wuajaxnoprivwuvalidateform AJAX handler accepting a freely obtainable checkout nonce, and the checkoutform=wu-finish-checkout parameter causing getvalidationrules() to discard all validation rules while finishcheckoutformfields() returns an empty step list — forcing islaststep() to return true and routing the request directly into full order processing — after which maybecreatecustomer() resolves the attacker-supplied emailaddress to an existing WordPress user ID without any authentication or ownership verification, and logincustomeraftercheckout() calls wpsetauthcookie() 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.
Affected Software
Event History
Frequently Asked Questions
Which plugin versions are affected?
All Ultimate Multisite versions up to and including 2.15.0 are affected.
Does an attacker need an account or valid credentials?
No. The vulnerable AJAX handler is publicly accessible, and the checkout nonce it accepts is described as freely obtainable. An attacker needs the email address of an existing WordPress user they intend to target.
Can this affect privileged WordPress accounts?
Yes. The issue can allow login as an existing WordPress user, including a Network Super Admin. The supplied description also indicates there is an additional target-account prerequisite, but that condition is truncated in the provided data.