A vulnerability in the smart card login authentication of Cisco Duo for macOS could allow an unauthenticated attacker with physical access to bypass authentication. This vulnerability exists because the assigned user of a smart card is not properly matched with the authenticating user. An attacker could exploit this vulnerability by configuring a smart card login to bypass Duo authentication. A successful exploit could allow the attacker to use any personal identity verification (PIV) smart card for authentication, even if the smart card is not assigned to the authenticating user.