CVE-2020-2050: 
PAN-OS vulnerability analysis and mitigation

An authentication bypass vulnerability (CVE-2020-2050) 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. The vulnerability was discovered internally by Nicholas Newsom of Palo Alto Networks and disclosed on November 11, 2020. It affects PAN-OS versions 8.1 (earlier than 8.1.17), 9.0 (earlier than 9.0.11), 9.1 (earlier than 9.1.5), and 10.0 (earlier than 10.0.1). The vulnerability has a CVSS score of 8.2 (HIGH) (Palo Advisory).

The vulnerability allows a remote attacker to 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. The impacted features include GlobalProtect Gateway, GlobalProtect Portal, GlobalProtect Clientless VPN, and GlobalProtect Large Scale VPN. In configurations where client certificate verification is used with other authentication methods, the protections added by the certificate check are ignored (Palo Advisory).

An attacker can bypass client certificate authentication and gain unauthorized access to restricted VPN network resources. This affects organizations using GlobalProtect VPN with client certificate authentication, potentially compromising network security by allowing unauthorized access (Palo Advisory).

Palo Alto Networks reported no evidence of active exploitation in the wild at the time of disclosure. The vulnerability requires no user interaction and can be exploited remotely with low attack complexity. The issue only affects systems using GlobalProtect VPN with client certificate authentication enabled (Palo Advisory).

The vulnerability is fixed in PAN-OS versions 8.1.17, 9.0.11, 9.1.5, 10.0.1, and all later versions. Until PAN-OS software can be upgraded, organizations can enable signatures for Unique Threat ID 59884 on traffic destined for the GlobalProtect portal, gateway, or VPN to block attacks. Additionally, configuring GlobalProtect to require users to authenticate with their credentials provides mitigation as other authentication methods are not impacted by this issue (Palo Advisory).