When the pre-logon feature is enabled, a missing certification validation in Palo Alto Networks GlobalProtect app can disclose the pre-logon authentication cookie to a man-in-the-middle attacker on the same local area network segment with the ability to manipulate ARP or to conduct ARP spoofing attacks. This allows the attacker to access the GlobalProtect Server as allowed by configured Security rules for the 'pre-login' user. This access may be limited compared to the network access of regular users. This issue affects: GlobalProtect app 5.0 versions earlier than GlobalProtect app 5.0.10 when the prelogon feature is enabled; GlobalProtect app 5.1 versions earlier than GlobalProtect app 5.1.4 when the prelogon feature is enabled.