Government cybersecurity agency warns of Windows Server exploit

Rare warning from CISA instructs government agencies to patch a vulnerability in a core authentication component of Active Directory from Windows Server 2008 to Windows Server 2019.

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The federal government's Cybersecurity and Infrastructure Security Agency (CISA) has issued a rare emergency directive to federal government agencies to roll out a Windows Server patch within days, an indication of the severity of the exploit.

The directive was issued on September 18, and agencies were given four days to apply the security update. It demands that executive agencies take "immediate and emergency action" to patch CVE-2020-1472, issued August 11.

The vulnerability is in Microsoft Windows Netlogon Remote Protocol (MS-NRPC), a core authentication component of Active Directory from Windows Server 2008 to Server 2019. It has been named "Zerologon" because of how it works.

CVE-2020-1472 addresses a critical elevation-of-privilege bug that exists when an attacker uses NRPC to establish a vulnerable secure channel connection to a domain controller, according to Microsoft's bug entry. It could allow an unauthenticated attacker with network access to a domain controller to completely compromise all Active Directory identity services.

Microsoft rated the exploit a 10 on the 1-10 Common Vulnerability Scoring System (CVSS) scale, meaning the most severe of vulnerabilities. The patch is the only way to mitigate this vulnerability, or the affected domain controllers could be removed from the network.

CISA has jurisdiction over government agencies, save for the Department of Defense, which has its own rules. However, CISA strongly urges state and local government agencies, the private sector, and other non-governmental entities to update as soon as possible.

When bug hunters find exploits like this, all parties do a pretty good job of keeping the details quiet until a patch is issued. The problem is that once a patch is issued, the vulnerability becomes available for all to see, and if the patch isn't immediately applied, those machines are at risk.