Wild Apricot Login <= 1.0.18 - Authentication Bypass via SSO Email-Collision Account Binding on Multisite

The Wild Apricot Login plugin for WordPress is vulnerable to Authentication Bypass via SSO Email-Collision Account Binding in all versions up to, and including, 1.0.18. When no WildApricot contact-ID mapping is found for an incoming SSO login, the plugin falls back to a network-global `get_user_by('email', ...)` lookup in `Module.php` to resolve a WordPress user, then `UserSynchronizer::syncWaContact()` binds and `Controller::login()` issues a session cookie via `wp_set_auth_cookie()` for that resolved user — both guarded only by `is_super_admin()` — without ever requiring proof of ownership of the matched WordPress account such as a password, local account-linking confirmation, inbox verification, or administrator approval. This makes it possible for attackers with custom-level WildApricot membership access to authenticate as an existing WordPress subsite administrator on a path-based Multisite network, obtaining a valid network-global authentication cookie for the victim without their credentials. Exploitation requires that the attacker control a WildApricot contact whose email address matches the target WordPress administrator's email — achievable via a public zero-fee membership application on the connected WildApricot organization — and that they complete the SSO flow on any subsite where Wild Apricot Login is active; because WordPress user identities and authentication cookies are network-global, the cookie issued on that subsite is equally valid on any other subsite where the victim user holds an administrator role.

Because it turns on account access, WordSec's login security is the relevant layer: role-based two-factor, captcha and brute-force limits raise the cost of getting the account this needs. No patched version is recorded yet, which is the case where a filtering layer matters most, because there is nothing to update to.

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