The SAML Single Sign On WordPress plugin before 6.0.0 does not honour the configured criterion...

The SAML Single Sign On WordPress plugin before 6.0.0 does not honour the configured criterion for linking an incoming single sign-on identity to a WordPress account, always resolving the identity by login name whatever the site has chosen, which allows an attacker who can have the site's identity provider assert a login name of their choosing to authenticate as any account, including an administrator, without proving ownership of that account.