We’ve looked at many vulnerabilities over the years here on Hackaday, but it’s rather rare for a CVE to score a perfect 10 severity. This is reserved for the most severe and exploitable of problems. Palo Alto announced such a vulnerability, CVE-2020-2021, on the 29th. This vulnerability affects Palo Alto devices running PAN-OS that have SAML authentication enabled and a certain validation option disabled. The vulnerability is pre-authentication, but does require access to a service protected by SAML authentication. For example, a Palo Alto device providing a web-based VPN could be vulnerable. The good news is that the vulnerable settings aren’t default, but the bad news is that the official configuration guide recommends the vulnerable settings for certain scenarios, like using a third party authentication service.
The issue is in the Security Assertion Markup Language (SAML) implementation, which is an XML based open standard for authentication. One of the primary use cases for SAML is to provide a Single Sign On (SSO) scheme. The normal deployment of SAML SSO is that a central provider handles the authentication of users, and then asserts to individual services that the connecting user is actually who they claim to be.
The setting needed for this vulnerability to be exploitable is ‘Validate Identity Provider Certificate’ to be disabled. If this option is enabled, the SSO provider must use a CA signed SAML certificates. This doesn’t appear to mean that unsigned SSL certificates would be accepted, and only applies to certificates inside the SAML messages. It seems to be widely accepted that these certificates don’t need to be CA signed. In the official announcement, the vulnerability type is said to be “CWE-347 Improper Verification of Cryptographic Signature”. Continue reading “This Week In Security: Palo Alto Scores A 10, Cursed Images, VM Escapes, And Malicious Music”