Microsoft today finally released software updates to patch a recently disclosed very dangerous vulnerability in SMBv3 protocol that could let attackers launch wormable malware, which propagates itself from one vulnerable computer to another automatically.

The vulnerability, tracked as CVE-2020-0796, in question is a remote code execution flaw that affects Windows 10 version 1903 and 1909, and Windows Server version 1903 and 1909.

Server Message Block (SMB), which runs over TCP port 445, is a network protocol that has been designed to enable file sharing, network browsing, printing services, and interprocess communication over a network.

The latest vulnerability, for which a patch update is now available on the Microsoft website, exists in the way SMBv3 protocol handles requests with compression headers, which makes it possible for an unauthenticated, remote attacker to execute malicious code on the target servers or clients.

Compression headers is a feature that was added to the affected protocol of the Windows 10 and Windows Server operating systems in May 2019.


"To exploit the vulnerability against a server, an unauthenticated attacker could send a specially crafted packet to a targeted SMBv3 server. To exploit the vulnerability against a client, an unauthenticated attacker would need to configure a malicious SMBv3 server and convince a user to connect to it," Microsoft said in the advisory.

At the time of writing, there is only one known PoC exploit that exists for this critical remotely exploitable flaw, but reverse engineering new patches could now also help others find possible real-life attack vectors.

Since a patch for the wormable SMBv3 flaw is now available to download for affected versions of Windows, it's highly recommended for home users and businesses to install updates as soon as possible, rather than merely relying on the mitigation.