CVE-2020-2021: Authentication Bypass in SAML Authentication

What it is

When Security Assertion Markup Language (SAML) authentication is enabled and the 'Validate Identity Provider Certificate' option is disabled (unchecked), improper verification of signatures in PAN-OS SAML authentication enables an unauthenticated network-based attacker to access protected resources. The attacker must have network access to the vulnerable server to exploit this vulnerability.

This issue affects PAN-OS 9.1 versions earlier than PAN-OS 9.1.3; PAN-OS 9.0 versions earlier than PAN-OS 9.0.9; PAN-OS 8.1 versions earlier than PAN-OS 8.1.15, and all versions of PAN-OS 8.0 (EOL). This issue does not affect PAN-OS 7.1.

This issue cannot be exploited if SAML is not used for authentication.

This issue cannot be exploited if the 'Validate Identity Provider Certificate' option is enabled (checked) in the SAML Identity Provider Server Profile.

Resources that can be protected by SAML-based single sign-on (SSO) authentication are: GlobalProtect Gateway, GlobalProtect Portal, GlobalProtect Clientless VPN, Authentication and Captive Portal, PAN-OS next-generation firewalls (PA-Series, VM-Series) and Panorama web interfaces, Prisma Access

In the case of GlobalProtect Gateways, GlobalProtect Portal, Clientless VPN, Captive Portal, and Prisma Access, an unauthenticated attacker with network access to the affected servers can gain access to protected resources if allowed by configured authentication and Security policies. There is no impact on the integrity and availability of the gateway, portal, or VPN server. An attacker cannot inspect or tamper with sessions of regular users. In the worst case, this is a critical severity vulnerability with a CVSS Base Score of 10.0 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N).

In the case of PAN-OS and Panorama web interfaces, this issue allows an unauthenticated attacker with network access to the PAN-OS or Panorama web interfaces to log in as an administrator and perform administrative actions. In the worst-case scenario, this is a critical severity vulnerability with a CVSS Base Score of 10.0 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H). If the web interfaces are only accessible to a restricted management network, then the issue is lowered to a CVSS Base Score of 9.6 (CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H).

Palo Alto Networks is not aware of any malicious attempts to exploit this vulnerability.

Am I affected?

This issue is applicable only where SAML authentication is enabled and the 'Validate Identity Provider Certificate' option is disabled (unchecked) in the SAML Identity Provider Server Profile. This issue cannot be exploited if SAML is not used for authentication. This issue cannot be exploited if the 'Validate Identity Provider Certificate' option is enabled in the SAML Identity Provider Server Profile. Detailed descriptions of how to check for the configuration required for exposure and mitigate them are listed in the knowledge base article https://knowledgebase.paloaltonetworks.com/KCSArticleDetail?id=kA14u0000008UXK. To check whether SAML authentication is enabled on a firewall, see the configuration under Device > Server Profiles > SAML Identity Provider. To check whether SAML authentication is enabled for Panorama administrator authentication, see the configuration under Panorama> Server Profiles > SAML Identity Provider To check whether SAML authentication is enabled for firewalls managed by Panorama, see the configuration under Device > [template]> Server Profiles > SAML Identity Provider. Any unauthorized access is logged in the system logs based on the configuration; however, it can be difficult to distinguish between valid and malicious logins or sessions.

Workarounds

Using a different authentication method and disabling SAML authentication will completely mitigate the issue. Until an upgrade can be performed, applying both these mitigations (a) and (b) eliminates the configuration required for exposure to this vulnerability:

(a) Ensure that the 'Identity Provider Certificate' is configured. Configuring the 'Identity Provider Certificate' is an essential part of a secure SAML authentication configuration.

(b) If the identity provider (IdP) certificate is a certificate authority (CA) signed certificate, then ensure that the 'Validate Identity Provider Certificate' option is enabled in the SAML Identity Provider Server Profile. Many popular IdPs generate self-signed IdP certificates by default and the 'Validate Identity Provider Certificate' option cannot be enabled. Additional steps may be required to use a certificate signed by a CA. This certificate can be signed by an internal enterprise CA, the CA on the PAN-OS, or a public CA. Instructions to configure a CA-issued certificate on IdPs are available at https://knowledgebase.paloaltonetworks.com/KCSArticleDetail?id=kA14u0000008UXP.

Upgrading to a fixed version of PAN-OS software prevents any future configuration changes related to SAML that inadvertently expose protected services to attacks.

Exploitation

Palo Alto Networks is not aware of any malicious attempts to exploit this vulnerability.

CISA lists this CVE as exploited in the wild since 25 Mar 2022, including in ransomware campaigns.