A remote code execution vulnerability exists when Windows Media Audio Codec improperly handles objects. An attacker who successfully exploited the vulnerability could take control of an affected system. There are multiple ways an attacker could exploit the vulnerability, such as by convincing a user to open a specially crafted document, or by convincing a user to visit a malicious webpage. The security update addresses the vulnerability by correcting how Windows Media Audio Codec handles objects.
https://www.tenable.com/blog/microsoft-s-august-2020-patch-tuesday-addresses-120-cves-cve-2020-1337
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-1339