CVE-2021-1730: Microsoft Exchange Server

Medium severity, CVSS 5.4. EPSS: 1.8% chance of exploitation in the next 30 days.

<p>A spoofing vulnerability exists in Microsoft Exchange Server which could result in an attack that would allow a malicious actor to impersonate the user.</p> <p>This update addresses this vulnerability.</p> <p>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.</p>

Affected products

• Microsoft Exchange Server: version 2016 only; version 2019 only

Published 2021-02-25. Last modified 2026-06-17.