Ultimate Multisite Plugin up to 2.16.x on WordPress improper authentication

Summaryinfo

A vulnerability was found in Ultimate Multisite Plugin up to 2.16.x and classified as critical. Affected by this vulnerability is an unknown functionality. The manipulation results in improper authentication. This vulnerability is reported as CVE-2026-103646. The attack can be launched remotely. No exploit exists. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as critical, was found in Ultimate Multisite Plugin up to 2.16.x. Affected is an unknown code. The manipulation with an unknown input leads to a improper authentication vulnerability. CWE is classifying the issue as CWE-287. When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct. This is going to have an impact on confidentiality, integrity, and availability. CVE summarizes:

The Ultimate Multisite WordPress plugin before 2.17.0 does not require authentication before a logged-out checkout is linked to, and logged in as, an existing WordPress account matching the submitted email address, and its duplicate-account check normalizes that address differently from the lookup used to create the customer, so an unauthenticated attacker can log in as any existing user, including a Network Super Admin, whose email address they know. This bypass is not addressed by the 2.15.1 fix for CVE-2026-75957 and remains exploitable in all versions up to and including 2.16.1, the releases that fix was expected to cover. Exploitation requires a checkout form configured without a password field (auto-generated password) and a target account that has no existing customer record in the Ultimate Multisite WordPress plugin before 2.17.0.

The advisory is shared for download at wpscan.com. This vulnerability is traded as CVE-2026-103646 since 10/01/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. There are neither technical details nor an exploit publicly available.

Upgrading to version 2.17.0 eliminates this vulnerability.

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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
• 2.16

CPE 2.3info

• 🔒
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CPE 2.2info

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• 🔒
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