What’s Vulnerable › Vulnerabilities
CVE-2026-103646: Ultimate Multisite < 2.17.0 - Unauthenticated Authentication Bypass via 'email_address' Parameter
- Severity: critical (CVSS 9.8 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 0.4% probability of exploitation in the next 30 days
- Public exploit or detection template: none known
- Published: 2026-10-08 · updated 2026-10-08
- Weakness: CWE-287
Description
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.
Affected products
- Ultimate Multisite: before 2.17.0 — fixed in 2.17.0
How to fix
Upgrade to a fixed version: Ultimate Multisite 2.17.0. Check the vendor advisory for mitigations.
References
Get alerted when CVE-2026-103646 or the next vulnerability affects your stack