The update fixes CVE-2020-0796 vulnerability in Server Message Block, a protocol for sharing files, printers, and other resources on local networks and the Internet.
The bug allowed attackers to connect to remote systems where SMB was enabled and to run malicious code with SYSTEM privileges.
Earlier this week, due to a leak of communication between Microsoft and some antivirus companies, details released for this particular internet error.
So although Microsoft had no plans to release other fixes this month, it was eventually forced to release the current patch.
Today's fixes were probably released on time, and according to the company the vulnerability only affects the Windows 10 and Windows Server 2019 (1903 and 1909).
For those who cannot install the update directly, Microsoft has detailed vulnerability information on a separate security advisory.