F5 BIG IP Vulnerable to Kerberos

A new bypass vulnerability in the Kerberos Key Distribution Center (KDC) security feature impacting F5 Big-IP application delivery services.

The KDC Spoofing vulnerability allows an attacker to bypass the Kerberos authentication to Big-IP Access Policy Manager (APM), bypass security policies and gain unfettered access to sensitive workloads,” bypassing F5 admin console

Kerberos is an authentication protocol that relies on a client-server model for mutual authentication and requires a trusted intermediary called Key Distribution Center A Kerberos Authentication Server (AS) or a Ticket Granting Server acts as a repository of shared secret keys of all users as well as information about which users have access privileges to which services on which network servers.

Thus when a user, say Alice, wants to access a particular service on a server (Bob), Alice is prompted to provide her username and password to verify her identity, after which the AS checks if Alice has access privileges to Bob, and if so, issue a “ticket” permitting the user to use the service until its expiration time.

As part of the process is the authentication of KDC to the server, in the absence of which the security of the Kerberos gets compromised, thus allowing an attacker that has the ability to hijack the network communication between Big-IP and the domain controller to sidestep the authentication entirely.

An adversary attempting to impersonate the KDC cannot bypass the authentication protections. The spoofing attack hinges on the possibility that there exist insecure Kerberos configurations so as to hijack the communication between the client and the domain controller, leveraging it to create a fraudulent KDC that diverts the traffic intended for the controller to the fake KDC, and subsequently authenticate itself to the client.

Patch is released to address the issue