Microsoft has released out-of-band (OOB) security updates to address vulnerabilities in IE11 & Defender from vulnerabilities that can be exploited by malware authors.

https://redmondmag.com/articles/2019/09/23/ie-and-microsoft-defender-security-advisories.aspx

https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2019-1367

https://www.us-cert.gov/ncas/current-activity/2019/09/23/microsoft-releases-out-band-security-updates

The Cybersecurity and Infrastructure Security Agency (CISA) encourages users and administrators to review Microsoft Security Advisories for CVE-2019-1367CVE-2019-1255, and Microsoft’s Cumulative security update for Internet Explorer and apply the necessary updates.