Hackers primed to exploit CVSS 10-rated flaw in Palo Alto's PAN-OS

US Cyber Command has urged Palo Alto customers to their patch PAN-OS networking systems before cyber criminals have the opportunity to exploit a highly critical authentication vulnerability.

Assigned a rare CVSS score of 10/10, the flaw dubbed CVE-2020-2021 can allow an attacker to bypass authentication procedures and access a device without needing to provide credentials.

The vulnerability is triggered when the Security Assertion Markup Language (SAML) is enabled and the ‘validate identity provider certificate’ option is disabled. This causes the improper verification of signatures in PAN-OS, allowing an attacker with network access to the vulnerable server to access protected resources. 

“Please patch all devices affected by CVE-2020-2021 immediately, especially if SAML is in use,” US Cyber Command has tweeted. “Foreign APTs will likely attempt exploit soon. We appreciate Palo Alto Networks’ proactive response to this vulnerability.”

PAN-OS is the software that runs all Palo Alto firewalls, offering customers complete visibility and control of the apps in use by all users in all locations across an enterprise network. 

The flaw, which has been fixed, 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, which has reached end-of-life. 

Moreover, the flaw can only be exploited if SAML is in use for authentication. Elements of PAN-OS overseen by SAML-based authentication include virtual private network (VPN), GlobalProtect Gateways, GlobalProtect Portal, Captive Portal and Prisma Access. 

Vulnerabilities assigned a 10/10 rating on the CVSS scale are rare, and normally mean the exploit is highly exploitable, easy to trigger, and require little or no additional privileges and user interaction.

Nevertheless, the company has not yet seen evidence of active exploitation in the wild, despite warnings from US Cyber Command of imminent attempts by foreign APTs. 

Palo Alto has urged customers to ensure the signing certificate for their SAML Identity Provider is configured as the ‘Identity Provider Certificate’ before they upgrade to a fixed version of PAN-OS.

As short-term mitigation, restarting firewalls and the Panorama web interface eliminates any unauthorised sessions on the web interface. 

For evidence of a compromise, the company has urged customers to examine Authentication Logs, User-ID Logs, ACC NEtwork Activity Source/Destination Regions, Customers Reports, and GlobalProtect Logs in PAN-OS 9.1.0 and above.