An information disclosure vulnerability exists when certain central processing units (CPU) speculatively access memory. An attacker who successfully exploited the vulnerability could read privileged data across trust boundaries. To exploit this vulnerability, an attacker would have to log on to an affected system and run a specially crafted application. The vulnerability would not allow an attacker to elevate user rights directly, but it could be used to obtain information that could be used to try to compromise the affected system further.
KB4550970: Windows 8.1 and Windows Server 2012 R2 April 2020 Security Update
KB4550965: Windows 7 and Windows Server 2008 R2 April 2020 Security Update
KB4550929: Windows 10 Version 1607 and Windows Server 2016 April 2020 Security Update
KB4549949: Windows 10 Version 1809 and Windows Server 2019 April 2020 Security Update
KB4549951: Windows 10 Version 1903 and Windows 10 Version 1909 April 2020 Security Update