The CE21 Suite plugin for WordPress is vulnerable to authentication bypass in versions up to, and including, 2.2.0. This is due to hardcoded encryption key in the 'ce21_authentication_phrase' function. This makes it possible for unauthenticated attackers to log in as any existing user on the site, such as an administrator, if they have access to the email.
https://plugins.trac.wordpress.org/changeset/3205463/ce21-suite#file3
https://plugins.trac.wordpress.org/browser/ce21-suite/trunk/single-sign-on-ce21.php?rev=3097700#L242