A spoofing vulnerability exists in Microsoft Exchange Server which could result in an attack that would allow a malicious actor to impersonate the user. This update addresses this vulnerability. To prevent these types of attacks, Microsoft recommends customers to download inline images from different DNSdomains than the rest of OWA. Please see further instructions in the FAQ to put in place this mitigations.
Security Updates for Microsoft Exchange Server (CVE-2021-1730) (February 2021)
Patch Tuesday - February 2021