Admins urged to patch Windows Server immediately to close vulnerability

IT administrators are being urged to prioritize installing a security patch for Windows Server that Microsoft issued in August to close a vulnerability in Active Directory.

Dubbed Zerologon, if exploited, an attacker could gain a foothold on an internal network to become domain admin with one click. According to security firm Secura, which discovered the bug, all that is required is for a connection to the Domain Controller to be possible from the attacker’s viewpoint.

While the patch has been available for over a month, it’s considered so serious that on Friday the U.S. Cybersecurity and Infrastructure Security Agency (CISA) issued an emergency order to all federal departments to update all Windows Servers with the domain controller role by midnight tonight Eastern time.

UPDATE: On Sept. 23 Microsoft said it is seeing this vulnerability being exploited by hackers.

CISA’s Canadian counterpart, the Canadian Centre for Cyber Security (CCCS) warned both public and private sector organizations on Sept. 16 to install the patch immediately.

Tracked as CVE-2020-1472, the exploit occurs when establishing a vulnerable Netlogon secure channel connection to a domain controller, using the Netlogon Remote Protocol. The Netlogon Remote Protocol (also called MS-NRPC) is an interface that is used exclusively by domain-joined devices. MS-NRPC includes an authentication method and a method of establishing a Netlogon secure channel.

By forging an authentication token for specific Netlogon functionality, an attacker can call a function to set the computer password of the domain controller to a known value. After that, the attacker can use this new password to take control over the domain controller and steal the credentials of a domain admin.

The updates enforce the specified Netlogon client behaviour to use secure RPC with Netlogon secure channel between member computers and Active Directory domain controllers. To provide Active Director forest protection, all domain controllers must be updated since they will enforce secure RPC with Netlogon secure channel. This includes read-only domain controllers.

The August patch issued by Microsoft is actually the first phase of a fix. Starting with updates to be issued Feb. 9, 2021, enforcement mode will be enabled on all Windows domain controllers, regardless of the registry setting. Domain Controllers will deny vulnerable connections from all non-compliant devices unless they are added to the “Domain controller: Allow vulnerable Netlogon secure channel connections” group policy.

Would you recommend this article?


Thanks for taking the time to let us know what you think of this article!
We'd love to hear your opinion about this or any other story you read in our publication.

Jim Love, Chief Content Officer, IT World Canada

Featured Download

Howard Solomon
Howard Solomon
Currently a freelance writer, I'm the former editor of and Computing Canada. An IT journalist since 1997, I've written for several of ITWC's sister publications including and Computer Dealer News. Before that I was a staff reporter at the Calgary Herald and the Brampton (Ont.) Daily Times. I can be reached at hsolomon [@]

Featured Articles

Cybersecurity in 2024: Priorities and challenges for Canadian organizations 

By Derek Manky As predictions for 2024 point to the continued expansion...

Survey shows generative AI is a top priority for Canadian corporate leaders.

Leaders are devoting significant budget to generative AI for 2024 Canadian corporate...

Related Tech News

Tech Jobs

Our experienced team of journalists and bloggers bring you engaging in-depth interviews, videos and content targeted to IT professionals and line-of-business executives.

Tech Companies Hiring Right Now