CVE-2026-75957 Ultimate Multisite <= 2.15.0 - Unauthenticated Authentication Bypass via 'checkout_form' Parameter
Unauthenticated attackers can log in as any existing WordPress user, including admins, by supplying their email address to a vulnerable AJAX handler.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-75957?
CVE-2026-75957 is a critical authentication bypass vulnerability in superdav42 Ultimate Multisite – WordPress Multisite SaaS & WaaS Platform, published on 1 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-287
Which versions are affected by CVE-2026-75957?
How do I fix CVE-2026-75957?
No fix has been published for CVE-2026-75957 yet. Limit exposure of the affected software until one is available.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-75957 being exploited?
There is no known exploitation of CVE-2026-75957 in the wild and no public exploit code.
Sources
Also known as GHSA-xr7j-wm8w-c5p4.