# CVE-2021-42321: Microsoft Exchange Server Remote Code Execution Vulnerability

CVE-2021-42321 is fixed in 4 products on 1 platform, first by KB5007409, released November 9, 2021. It is being exploited: CISA added it to the Known Exploited Vulnerabilities catalog on November 17, 2021, with known ransomware use. Patch Radar priority: Patch now.

- Web page: https://patchblox.com/security/cve/CVE-2021-42321
- Priority: Patch now
- CVSS: 8.8 (Important)
- EPSS: 0.9174
- CISA KEV: listed Nov 17, 2021, federal due date Dec 1, 2021, known ransomware use
- Exploited (vendor report): yes
- Publicly disclosed: no
- Vendor exploitability assessment: Exploitation Detected
- Published: Nov 17, 2021
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-42321

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Microsoft | Microsoft Exchange Server 2016 Cumulative Update 21 |  | [KB5007409](https://patchblox.com/security/data/fix/microsoft/kb5007409.md) | Nov 9, 2021 |
| Microsoft | Microsoft Exchange Server 2016 Cumulative Update 22 |  | [KB5007409](https://patchblox.com/security/data/fix/microsoft/kb5007409.md) | Nov 9, 2021 |
| Microsoft | Microsoft Exchange Server 2019 Cumulative Update 10 |  | [KB5007409](https://patchblox.com/security/data/fix/microsoft/kb5007409.md) | Nov 9, 2021 |
| Microsoft | Microsoft Exchange Server 2019 Cumulative Update 11 |  | [KB5007409](https://patchblox.com/security/data/fix/microsoft/kb5007409.md) | Nov 9, 2021 |

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Data as of 2026-11-09T13:31:49Z 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 Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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