An authentication bypass vulnerability exists in the GlobalProtect SSL VPN component of Palo Alto Networks PAN-OS software that allows an attacker to bypass all client certificate checks with an invalid certificate. A remote attacker can successfully authenticate as any user and gain access to restricted VPN network resources when the gateway or portal is configured to rely entirely on certificate-based authentication. Impacted features that use SSL VPN with client certificate verification are: GlobalProtect Gateway, GlobalProtect Portal, GlobalProtect Clientless VPN In configurations where client certificate verification is used in conjunction with other authentication methods, the protections added by the certificate check are ignored as a result of this issue. This issue impacts: PAN-OS 8.1 versions earlier than PAN-OS 8.1.17; PAN-OS 9.0 versions earlier than PAN-OS 9.0.11; PAN-OS 9.1 versions earlier than PAN-OS 9.1.5; PAN-OS 10.0 versions earlier than PAN-OS 10.0.1.