Researchers have developed and published a proof-of-concept exploit for a recently patched Windows vulnerability that can allow access to an organization’s crown jewels—the Active Directory domain controllers that act as an all-powerful gatekeeper for all machines connected to a network.
Enter Zerologon, an exploit developed by researchers from security firm Secura.
“This attack has a huge impact,” researchers with Secura wrote in a white paper published on Friday.
“It basically allows any attacker on the local network (such as a malicious insider or someone who simply plugged in a device to an on-premise network port) to completely compromise the Windows domain.
The Secura researchers, who discovered the vulnerability and reported it to Microsoft, said they developed an exploit that works reliably, but given the risk, they aren’t releasing it until they’re confident Microsoft’s patch has been widely installed on vulnerable servers.
The researchers, however, warned that it’s not hard to use Microsoft’s patch to work backwards and develop an exploit.
The release and description of exploit code quickly caught the attention of the US Cybersecurity and Infrastructure Security Agency, which works to improve cybersecurity across all levels of government.
Zerologon works by sending a string of zeros in a series of messages that use the Netlogon protocol, which Windows servers rely on for a variety of tasks, including allowing end users to log in to a network.
People with no authentication can use the exploit to gain domain administrative credentials, as long as the attackers have the ability to establish TCP connections with a vulnerable domain controller.
The vulnerability stems from the Windows implementation of AES-CFB8, or the use of the AES cryptography protocol with cipher feedback to encrypt and validate authentication messages as they traverse the internal network.
The Secura writeup gives a deep dive on the cause of the vulnerability and the five-step approach to exploiting it.
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