Ultimate Multisite < 2.17.0 - Unauthenticated Authentication Bypass via 'email_address' Parameter

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.

Source published

8 Oct 2026 06:00:05 UTC

Source modified

8 Oct 2026 10:59:19 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

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