# KB5000871: March 2021 security update KB5000871, released March 10, 2021, fixes 7 CVEs across 25 products. 4 of them are being exploited (CVE-2021-26855); 4 on CISA KEV. Patch Radar priority: Patch now. The product is no longer supported. - Web page: https://patchblox.com/security/fix/microsoft/kb5000871 - Platform: Microsoft - Released: Mar 10, 2021 - Priority: Patch now (Closes CVE-2021-26855, exploited (CISA KEV, ransomware)) - CVEs: 7, exploited: 4, on CISA KEV: 4 - Vendor advisory: https://support.microsoft.com/help/5000871 ## Applies to | Product | Release | Fixed in | |---|---|---| | [Microsoft Exchange Server 2013 Cumulative Update 21](https://patchblox.com/security/data/product/microsoft/microsoft-exchange-server-2013-cumulative-update-21.md) | | | | [Microsoft Exchange Server 2013 Cumulative Update 22](https://patchblox.com/security/data/product/microsoft/microsoft-exchange-server-2013-cumulative-update-22.md) | | | | [Microsoft Exchange Server 2013 Cumulative Update 23](https://patchblox.com/security/data/product/microsoft/microsoft-exchange-server-2013-cumulative-update-23.md) | | | | [Microsoft Exchange Server 2013 Service Pack 1](https://patchblox.com/security/data/product/microsoft/microsoft-exchange-server-2013-service-pack-1.md) | | | | [Microsoft Exchange Server 2016 Cumulative Update 10](https://patchblox.com/security/data/product/microsoft/microsoft-exchange-server-2016-cumulative-update-10.md) | | | | [Microsoft Exchange Server 2016 Cumulative Update 11](https://patchblox.com/security/data/product/microsoft/microsoft-exchange-server-2016-cumulative-update-11.md) | | | | [Microsoft Exchange Server 2016 Cumulative Update 12](https://patchblox.com/security/data/product/microsoft/microsoft-exchange-server-2016-cumulative-update-12.md) | | | | [Microsoft Exchange Server 2016 Cumulative Update 13](https://patchblox.com/security/data/product/microsoft/microsoft-exchange-server-2016-cumulative-update-13.md) | | | | [Microsoft Exchange Server 2016 Cumulative Update 14](https://patchblox.com/security/data/product/microsoft/microsoft-exchange-server-2016-cumulative-update-14.md) | | | | [Microsoft Exchange Server 2016 Cumulative Update 15](https://patchblox.com/security/data/product/microsoft/microsoft-exchange-server-2016-cumulative-update-15.md) | | | | [Microsoft Exchange Server 2016 Cumulative Update 16](https://patchblox.com/security/data/product/microsoft/microsoft-exchange-server-2016-cumulative-update-16.md) | | | | [Microsoft Exchange Server 2016 Cumulative Update 17](https://patchblox.com/security/data/product/microsoft/microsoft-exchange-server-2016-cumulative-update-17.md) | | | | [Microsoft Exchange Server 2016 Cumulative Update 18](https://patchblox.com/security/data/product/microsoft/microsoft-exchange-server-2016-cumulative-update-18.md) | | | | [Microsoft Exchange Server 2016 Cumulative Update 19](https://patchblox.com/security/data/product/microsoft/microsoft-exchange-server-2016-cumulative-update-19.md) | | | | [Microsoft Exchange Server 2016 Cumulative Update 8](https://patchblox.com/security/data/product/microsoft/microsoft-exchange-server-2016-cumulative-update-8.md) | | | | [Microsoft Exchange Server 2016 Cumulative Update 9](https://patchblox.com/security/data/product/microsoft/microsoft-exchange-server-2016-cumulative-update-9.md) | | | | [Microsoft Exchange Server 2019](https://patchblox.com/security/data/product/microsoft/microsoft-exchange-server-2019.md) | | | | [Microsoft Exchange Server 2019 Cumulative Update 1](https://patchblox.com/security/data/product/microsoft/microsoft-exchange-server-2019-cumulative-update-1.md) | | | | [Microsoft Exchange Server 2019 Cumulative Update 2](https://patchblox.com/security/data/product/microsoft/microsoft-exchange-server-2019-cumulative-update-2.md) | | | | [Microsoft Exchange Server 2019 Cumulative Update 3](https://patchblox.com/security/data/product/microsoft/microsoft-exchange-server-2019-cumulative-update-3.md) | | | | [Microsoft Exchange Server 2019 Cumulative Update 4](https://patchblox.com/security/data/product/microsoft/microsoft-exchange-server-2019-cumulative-update-4.md) | | | | [Microsoft Exchange Server 2019 Cumulative Update 5](https://patchblox.com/security/data/product/microsoft/microsoft-exchange-server-2019-cumulative-update-5.md) | | | | [Microsoft Exchange Server 2019 Cumulative Update 6](https://patchblox.com/security/data/product/microsoft/microsoft-exchange-server-2019-cumulative-update-6.md) | | | | [Microsoft Exchange Server 2019 Cumulative Update 7](https://patchblox.com/security/data/product/microsoft/microsoft-exchange-server-2019-cumulative-update-7.md) | | | | [Microsoft Exchange Server 2019 Cumulative Update 8](https://patchblox.com/security/data/product/microsoft/microsoft-exchange-server-2019-cumulative-update-8.md) | | | ## CVEs this fix closes | CVE | Priority | Component | CVSS | EPSS | Exploitation | |---|---|---|---:|---:|---| | [CVE-2021-26855](https://patchblox.com/security/data/cve/CVE-2021-26855.md) | Patch now | Microsoft Exchange Server | 9.1 | 1.0000 | CISA KEV, Ransomware | | [CVE-2021-27065](https://patchblox.com/security/data/cve/CVE-2021-27065.md) | Patch now | Microsoft Exchange Server | 7.8 | 0.9988 | CISA KEV, Ransomware | | [CVE-2021-26857](https://patchblox.com/security/data/cve/CVE-2021-26857.md) | Patch now | Microsoft Exchange Server | 7.8 | 0.9576 | CISA KEV, Ransomware | | [CVE-2021-26858](https://patchblox.com/security/data/cve/CVE-2021-26858.md) | Patch now | Microsoft Exchange Server | 7.8 | 0.9365 | CISA KEV, Ransomware | | [CVE-2021-26412](https://patchblox.com/security/data/cve/CVE-2021-26412.md) | Urgent | Microsoft Exchange Server | 9.1 | 0.3376 | | | [CVE-2021-27078](https://patchblox.com/security/data/cve/CVE-2021-27078.md) | High | Microsoft Exchange Server | 9.1 | 0.2159 | | | [CVE-2021-26854](https://patchblox.com/security/data/cve/CVE-2021-26854.md) | Routine | Microsoft Exchange Server | 6.6 | 0.2474 | | --- Data as of 2026-11-07T06:34:28Z 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