# CVE-2021-26858: Microsoft Exchange Server Remote Code Execution Vulnerability

CVE-2021-26858 is fixed in 24 products on 1 platform, first by KB5000871, released March 10, 2021. It is being exploited: CISA added it to the Known Exploited Vulnerabilities catalog on November 3, 2021, with known ransomware use. Patch Radar priority: Patch now.

- Web page: https://patchblox.com/security/cve/CVE-2021-26858
- Priority: Patch now
- CVSS: 7.8 (Important)
- EPSS: 0.9365
- CISA KEV: listed Nov 3, 2021, federal due date May 3, 2022, known ransomware use
- Exploited (vendor report): yes
- Publicly disclosed: no
- Vendor exploitability assessment: Exploitation Detected
- Published: Mar 10, 2021
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-26858

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Microsoft | Microsoft Exchange Server 2013 Cumulative Update 21 |  | [KB5000871](https://patchblox.com/security/data/fix/microsoft/kb5000871.md) | Mar 10, 2021 |
| Microsoft | Microsoft Exchange Server 2013 Cumulative Update 22 |  | [KB5000871](https://patchblox.com/security/data/fix/microsoft/kb5000871.md) | Mar 10, 2021 |
| Microsoft | Microsoft Exchange Server 2013 Cumulative Update 23 |  | [KB5000871](https://patchblox.com/security/data/fix/microsoft/kb5000871.md) | Mar 10, 2021 |
| Microsoft | Microsoft Exchange Server 2016 Cumulative Update 10 |  | [KB5000871](https://patchblox.com/security/data/fix/microsoft/kb5000871.md) | Mar 10, 2021 |
| Microsoft | Microsoft Exchange Server 2016 Cumulative Update 11 |  | [KB5000871](https://patchblox.com/security/data/fix/microsoft/kb5000871.md) | Mar 10, 2021 |
| Microsoft | Microsoft Exchange Server 2016 Cumulative Update 12 |  | [KB5000871](https://patchblox.com/security/data/fix/microsoft/kb5000871.md) | Mar 10, 2021 |
| Microsoft | Microsoft Exchange Server 2016 Cumulative Update 13 |  | [KB5000871](https://patchblox.com/security/data/fix/microsoft/kb5000871.md) | Mar 10, 2021 |
| Microsoft | Microsoft Exchange Server 2016 Cumulative Update 14 |  | [KB5000871](https://patchblox.com/security/data/fix/microsoft/kb5000871.md) | Mar 10, 2021 |
| Microsoft | Microsoft Exchange Server 2016 Cumulative Update 15 |  | [KB5000871](https://patchblox.com/security/data/fix/microsoft/kb5000871.md) | Mar 10, 2021 |
| Microsoft | Microsoft Exchange Server 2016 Cumulative Update 16 |  | [KB5000871](https://patchblox.com/security/data/fix/microsoft/kb5000871.md) | Mar 10, 2021 |
| Microsoft | Microsoft Exchange Server 2016 Cumulative Update 17 |  | [KB5000871](https://patchblox.com/security/data/fix/microsoft/kb5000871.md) | Mar 10, 2021 |
| Microsoft | Microsoft Exchange Server 2016 Cumulative Update 18 |  | [KB5000871](https://patchblox.com/security/data/fix/microsoft/kb5000871.md) | Mar 10, 2021 |
| Microsoft | Microsoft Exchange Server 2016 Cumulative Update 19 |  | [KB5000871](https://patchblox.com/security/data/fix/microsoft/kb5000871.md) | Mar 10, 2021 |
| Microsoft | Microsoft Exchange Server 2016 Cumulative Update 8 |  | [KB5000871](https://patchblox.com/security/data/fix/microsoft/kb5000871.md) | Mar 10, 2021 |
| Microsoft | Microsoft Exchange Server 2016 Cumulative Update 9 |  | [KB5000871](https://patchblox.com/security/data/fix/microsoft/kb5000871.md) | Mar 10, 2021 |
| Microsoft | Microsoft Exchange Server 2019 |  | [KB5000871](https://patchblox.com/security/data/fix/microsoft/kb5000871.md) | Mar 10, 2021 |
| Microsoft | Microsoft Exchange Server 2019 Cumulative Update 1 |  | [KB5000871](https://patchblox.com/security/data/fix/microsoft/kb5000871.md) | Mar 10, 2021 |
| Microsoft | Microsoft Exchange Server 2019 Cumulative Update 2 |  | [KB5000871](https://patchblox.com/security/data/fix/microsoft/kb5000871.md) | Mar 10, 2021 |
| Microsoft | Microsoft Exchange Server 2019 Cumulative Update 3 |  | [KB5000871](https://patchblox.com/security/data/fix/microsoft/kb5000871.md) | Mar 10, 2021 |
| Microsoft | Microsoft Exchange Server 2019 Cumulative Update 4 |  | [KB5000871](https://patchblox.com/security/data/fix/microsoft/kb5000871.md) | Mar 10, 2021 |
| Microsoft | Microsoft Exchange Server 2019 Cumulative Update 5 |  | [KB5000871](https://patchblox.com/security/data/fix/microsoft/kb5000871.md) | Mar 10, 2021 |
| Microsoft | Microsoft Exchange Server 2019 Cumulative Update 6 |  | [KB5000871](https://patchblox.com/security/data/fix/microsoft/kb5000871.md) | Mar 10, 2021 |
| Microsoft | Microsoft Exchange Server 2019 Cumulative Update 7 |  | [KB5000871](https://patchblox.com/security/data/fix/microsoft/kb5000871.md) | Mar 10, 2021 |
| Microsoft | Microsoft Exchange Server 2019 Cumulative Update 8 |  | [KB5000871](https://patchblox.com/security/data/fix/microsoft/kb5000871.md) | Mar 10, 2021 |

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Data as of 2026-11-09T01:18:40Z 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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