Troubleshoot ‘Kerberos Pre-Auth Failed’ in Minutes

Ah Kerberos pre-authentication failed. We’ve all been there haven’t we? Trying to log in to a system and being met with that dreaded error message. It’s enough to make you want to pull your hair out.

Overview

Kerberos pre-authentication failed errors can be caused by many things from network issues to incorrect user credentials. In this article we’ll take a look at the most common causes and how to go about resolving them.

What is Kerberos Preauthentication?

Kerberos preauthentication is a security protocol that provides authentication services to help protect networks from malicious attacks. Put simply preauthentication ensures that users who attempt to log in are who they say they are. It’s the way you can make sure your password isn’t stolen by a nefarious hacker as it verifies the identity of the user before providing access to the network.

To use preauthentication a user must first authenticate themselves by providing a correct username and password or other credentials. That information is then checked against an authentication server. If the credentials supplied match what is stored in the server then the user is granted access.

Imagine a world where anyone could simply log in to any network at any time—that would be a scary place indeed! Preauthentication makes sure the right people get in and the wrong people stay out.

Unfortunately preauthentication isn’t perfect. It can fail due to various factors such as incorrect server configurations or incorrect user credentials. But when it works correctly preauthentication is a highly effective means of keeping networks secure.

Issues that Cause Preauthentication Failure

Have you ever seen the dreaded “Kerberos pre-authentication failed” message? If so then you know it can be a bit of a head-scratcher. It can stem from a variety of issues leaving you feeling frustrated and unsure of how to proceed. To help you get to the bottom of things we’ve outlined some of the most common causes of pre-authentication failure.

First let’s look at user account issues. It’s possible for a user’s status to be disabled or expired. This can be due to an administrator manually disabling an account a password policy set to expire them after a certain period of time or even a network policy that kicks inactive users off after some time of inactivity. To get around this you should simply re-enable their account or change the password policy settings.

Another common cause of pre-authentication failure is network connection issues. If a user is attempting to log in with a computer connected to the wrong domain the Kerberos authentication will fail. Be sure the user is connected to the correct domain so Kerberos can properly authenticate them.

Finally any number of software issues could be at the heart of the pre-authentication failure. If the user’s machine does not have the correct version of the Kerberos protocol installed the authentication will fail. It can also be caused by outdated DNS configuration settings or something as simple as clock synchronization problems between machines in the domain.

As you can see there are many potential issues that could cause a pre-authentication failure. To get to the root of the problem you should examine user accounts network connections and software settings before diving into solutions. With these points in mind you should be able to figure out why you’re facing a pre-authentication failure and hopefully get back on track quickly.

Troubleshooting and Prevention

Ah the classic ‘Kerberos Pre-Authentication Failed’ issue! It can be an absolute headache when this pops up but fear not – with a few key steps we’ll get you up and running in no time. Let’s get straight into the nitty-gritty of troubleshooting and prevention methods.

The first step is to check on the clock and time zone settings of your client and server machines. Make sure they are in sync as Kerberos will not authenticate if the clocks are out of sync. You’ll want to check your Active Directory for this as well as the Windows Time Service on both the client and server machines.

Next you should check if DNS is resolving correctly. If DNS cannot find the domain controller authentication cannot happen.

Finally check if there is a valid host principal for the target server in the domain controller’s key distribution center. The client machine should attempt to communicate with the key distribution center using the correct host principal in order for the authentication to take place.

Prevention is the best cure in these types of scenarios. Consider setting up a Kerberos monitoring system. This system will alert you whenever there is a Kerberos pre-authentication failure. It can also monitor active directory replication as well as time and DNS issues that may be causing such errors.

We’ve also found that creating a schedule for rebooting the client and server machines can help preemptively solve Kerberos pre-authentication errors. It’s important to note that you’ll need to reboot both the server and client machines for this to take effect.

If you follow these troubleshooting and prevention steps you’ll find that ‘Kerberos Pre-Authentication Failed’ issue disappear before your eyes. Keep at it and you’ll be back up and running in no time!

Resources

• https://computing.fnal.gov/lqcd/troubleshooting-kerberos-kinit-problems/