Authentication flaw

The WP User Switch plugin for WordPress is vulnerable to authentication bypass in versions up to, and including, 1.0.2. This is due to incorrect authentication checking in the ‘wpus_allow_user_to_admin_bar_menu’ function with the ‘wpus_who_switch’ cookie value. This makes it possible for authenticated attackers, with subscriber-level permissions and above, to log in as any existing user on the site, such as an administrator, if they have access to the username.