What’s Vulnerable › Vulnerabilities

CVE-2021-1730: Microsoft Exchange Server Spoofing Vulnerability

• Severity: medium (CVSS 5.8 v2.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.8% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-02-25 · updated 2026-06-17

Description

<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: 2016-cumulative_update_18, 2019-cumulative_update_7
• Microsoft Exchange Server 2016 Cumulative Update 18: from 15.01.0 before publication — fixed in publication
• Microsoft Exchange Server 2019 Cumulative Update 7: from 15.02.0 before publication — fixed in publication

How to fix

Upgrade to a fixed version: Microsoft Exchange Server 2016 Cumulative Update 18 publication; Microsoft Exchange Server 2019 Cumulative Update 7 publication. Check the vendor advisory for mitigations.

References

• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-1730
• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-1730

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