Ultimate Multisite Plugin up to 2.15.0 on WordPress Ajax login_customer_after_checkout checkout_form improper authentication

Summaryinfo

A vulnerability identified as critical has been detected in Ultimate Multisite Plugin up to 2.15.0. This affects the function login_customer_after_checkout of the component Ajax Handler. This manipulation of the argument checkout_form causes improper authentication. The identification of this vulnerability is CVE-2026-75957. It is possible to initiate the attack remotely. There is no exploit available.

Detailsinfo

A vulnerability has been found in Ultimate Multisite Plugin up to 2.15.0 and classified as critical. Affected by this vulnerability is the function login_customer_after_checkout of the component Ajax Handler. The manipulation of the argument checkout_form with an unknown input leads to a improper authentication vulnerability. The CWE definition for the vulnerability is CWE-287. When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

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.

It is possible to read the advisory at wordfence.com. This vulnerability is known as CVE-2026-75957 since 08/18/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Technical details of the vulnerability are known, but there is no available exploit. The pricing for an exploit might be around USD $0-$5k at the moment (estimation calculated on 10/01/2026).

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

Be aware that VulDB is the high quality source for vulnerability data.

Productinfo

Type

• WordPress Plugin

Name

• Ultimate Multisite Plugin

Version

• 2.0
• 2.1
• 2.2
• 2.3
• 2.4
• 2.5
• 2.6
• 2.7
• 2.8
• 2.9
• 2.10
• 2.11
• 2.12
• 2.13
• 2.14
• 2.15.0

CPE 2.3info

• 🔒
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CPE 2.2info

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• 🔒

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Entryinfo

Be aware that VulDB is the high quality source for vulnerability data.

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