Microsoft will Enable Domain Controller Enforcement Mode to Address Zerologon Flaw

In a post on 14^th January 2021, Microsoft’s Aanchal Gupta, VP Engineering, published a post alerting network admins that an upcoming Windows Security Update will ensure that the Domain Controller enforcement mode will be enabled by default.

Vulnerability that was found

It was earlier identified that a malicious attacker by using the Netlogon Remote Protocol (MS-NRPC), could establish a vulnerable Netlogon secure channel connection to a domain controller. Once this vulnerability had been exploited, the threat actor could run a specially crafted application on a device on the network.

Benefit of the Security update

Once the update has been successfully completed, devices will connect only using the secure RPC with Netlogon secure channel, unless the customer has specifically added an exception for the non-compliant device thus making it vulnerable.

“We are reminding our customers that beginning with the February 9, 2021 Security Update release we will be enabling Domain Controller enforcement mode by default. This will block vulnerable connections from non-compliant devices,” Microsoft notes.

Things to do

To prepare, network admins need to:

• UPDATE their Domain Controllers with an update released August 11, 2020 or later.
• FIND which devices are making vulnerable connections by monitoring event logs.
• ADDRESS non-compliant devices making vulnerable connections.
• ENABLE Domain Controller enforcement mode to address CVE-2020-1472 in your environment

In preparation for the enforcement mode phase, organizations should apply the available patch to all domain controllers and should identify and resolve non-compliant devices to ensure they won’t make vulnerable connections.

Previous attacks

In the latter half of 2020, the Netlogon vulnerability CVE-2020-1472 was used by a group of hackers to attack several networks by using the Ryuk ransomware.