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 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.
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| WordPress plugin | Ultimate Multisite – WordPress Multisite SaaS & WaaS Platform | <= 2.15.0 | 2.15.1 |
References
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H- Weakness (CWE)
CWE-287- Platform
- WordPress
- Package
Ultimate Multisite – WordPress Multisite SaaS & WaaS Platform- Disclosed
- 30.09.2026
- Updated
- 11.10.2026 10:22
Sources and licenses
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Vulnerability history: Ultimate Multisite – WordPress Multisite SaaS & WaaS Platform
All published vulnerabilities of this package (WordPress plugin), newest first. Shows whether this is a one-off slip or a package that needs watching.
This is the only known vulnerability of this package.
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