# CVE-2021-1730: Microsoft Exchange Server Spoofing Vulnerability

CVE-2021-1730 is fixed in 2 products on 1 platform, first by KB4571788, released February 9, 2021. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2021-1730
- Priority: Routine
- CVSS: 5.4 (Important)
- EPSS: 0.0182
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Vendor exploitability assessment: Exploitation Less Likely
- Published: Feb 9, 2021
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-1730

## 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>

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Microsoft | Microsoft Exchange Server 2016 Cumulative Update 18 |  | [KB4571788](https://patchblox.com/security/data/fix/microsoft/kb4571788.md) | Feb 9, 2021 |
| Microsoft | Microsoft Exchange Server 2019 Cumulative Update 7 |  | [KB4571787](https://patchblox.com/security/data/fix/microsoft/kb4571787.md) | Feb 9, 2021 |

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Data as of 2026-11-08T13:06:02Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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