One of the security vulnerabilities fixed on Tuesday 11 August (Patch Tuesday) affects Windows 7, Windows 8.1, Windows 10, and several versions of Windows Server, and Microsoft itself has reported attacks that use this flaw.
It is a forgery vulnerability in the operating system and documented in CVE-2020-1464.
"There is a vulnerability to forgery when Windows incorrectly validates file signatures. An attacker who successfully exploits this vulnerability could override security features and upload files that have not been properly signed. "In an attack scenario, an attacker could bypass security features to prevent improperly signed files from being loaded."
The company knew that exploit was operating and that it was publicly disclosed in 2018.
KrebsOnSercurity reveals that the forgery vulnerability was reported to Microsoft by Bernardo Quintero, director of VirusTotal.
"Microsoft has decided not to resolve this issue in the current versions of Windows and has agreed that we may publish this exploit." refers in Virus Total.
Tal Be'ery, security researcher and founder of KZen Networks, also points out that the flaw was discovered in the summer of 2018 and somehow Microsoft decided not to fix it.
Microsoft, on the other hand, does not answer why it left its customers' devices exposed for so long from 2018 and waiting until August 2020 to resolve the defect.
Note that devices running Windows 7, which are themselves exposed to the same attack, will not be updated as support expired in January 2020.