This blog was originally published Sept. 18, 2020 on humio.com. Humio is a CrowdStrike Company.

Zerologon is arguably the most dangerous Windows vulnerability the security industry has seen. Organizations want to know with no uncertainty whether they’ve been attacked. That assurance doesn’t come from searching 30 days or even 90 days’ worth of Windows logs. It comes from a comprehensive search of all your Windows logs. Humio customers can get the certainty they need in a matter of seconds.

Last month, Microsoft issued a patch for Zerologon. Since then, the severity of the vulnerability has come to light. The bug, identified as CVE-2020-1472, has a Common Vulnerability Scoring System (CVSS) score of 10.0.

When left unpatched, Zerologon allows an attacker to manipulate Netlogon authentication procedures by adding zeros to Netlogon authentication parameters. To exploit the bug, an attacker must already have access to the enterprise network. From there, however, attackers can take control of any part of an enterprise Windows infrastructure or the entire network–in a matter of seconds. The example exploit code is a trivial Python script of less than 100 lines. It can be executed in seconds, giving an attacker full administrative control of the domain controller.

If your organization uses Humio for log management, you have the benefit of querying all of your Windows logs to determine whether your environment has been compromised.

At the request of a customer who was looking to detect the Zerologon attack in their own logs, we wrote a query for this purpose. Running this one query across relevant Windows logs will let you know, in a matter of seconds, if you’ve been impacted by Zerologon.

"NetrServerPasswordSet2" OR "NetrServerReqChallenge" OR "NetrServerAuthenticate3"
| groupBy(ipAddress, function=[ { "NetrServerPasswordSet2" | count(as=NetrServerPasswordSet2) },
{ "NetrServerReqChallenge" | count(as=NetrServerReqChallenge) },
{ "NetrServerAuthenticate3" | count(as=NetrServerAuthenticate3)}])
| NetrServerReqChallenge > 2 AND NetrServerAuthenticate3 > 0 AND NetrServerPasswordSet2 > 0

This is not the most efficient form of the query, but it is the most versatile. There’s little need to format the data in any way (only the IP address needs to be parsed in advance), making it a quick and easy way to query your Windows logs for Zerologon. We advise you to run this query as soon as possible, and hopefully you–and your executives–can rest assured when you see the results.

Want to learn more about using Humio for security? Listen to this on-demand webinar with our partner, Vijilan. Also learn how to simplify the ingestion of Office 365 logs into Humio with O365beat.