# KB5003435: May 2021 security update

KB5003435, released May 11, 2021, fixes 4 CVEs across 5 products. One of them is being exploited (CVE-2021-31207); 1 on CISA KEV. Patch Radar priority: Patch now. The product is no longer supported.

- Web page: https://patchblox.com/security/fix/microsoft/kb5003435
- Platform: Microsoft
- Released: May 11, 2021
- Priority: Patch now (Closes CVE-2021-31207, exploited (CISA KEV, ransomware))
- CVEs: 4, exploited: 1, on CISA KEV: 1
- Vendor advisory: https://support.microsoft.com/help/5003435

## Applies to

| Product | Release | Fixed in |
|---|---|---|
| [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 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 20](https://patchblox.com/security/data/product/microsoft/microsoft-exchange-server-2016-cumulative-update-20.md) |  |  |
| [Microsoft Exchange Server 2019 Cumulative Update 8](https://patchblox.com/security/data/product/microsoft/microsoft-exchange-server-2019-cumulative-update-8.md) |  |  |
| [Microsoft Exchange Server 2019 Cumulative Update 9](https://patchblox.com/security/data/product/microsoft/microsoft-exchange-server-2019-cumulative-update-9.md) |  |  |

## CVEs this fix closes

| CVE | Priority | Component | CVSS | EPSS | Exploitation |
|---|---|---|---:|---:|---|
| [CVE-2021-31207](https://patchblox.com/security/data/cve/CVE-2021-31207.md) | Patch now | Microsoft Exchange Server | 6.6 | 0.9978 | CISA KEV, Ransomware, Disclosed |
| [CVE-2021-31198](https://patchblox.com/security/data/cve/CVE-2021-31198.md) | High | Microsoft Exchange Server | 7.8 | 0.0487 |  |
| [CVE-2021-31195](https://patchblox.com/security/data/cve/CVE-2021-31195.md) | Routine | Microsoft Exchange Server | 6.5 | 0.7368 |  |
| [CVE-2021-31209](https://patchblox.com/security/data/cve/CVE-2021-31209.md) | Routine | Microsoft Exchange Server | 6.5 | 0.0263 |  |

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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 Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo