# KB5001999: September 2021 security update

KB5001999, released September 14, 2021, fixes 1 CVE in Microsoft Office Online Server. None of them is reported as exploited. Patch Radar priority: High. The product is no longer supported.

- Web page: https://patchblox.com/security/fix/microsoft/kb5001999
- Platform: Microsoft
- Released: Sep 14, 2021
- Priority: High (Closes CVE-2021-38655, high severity)
- CVEs: 1, exploited: 0, on CISA KEV: 0
- Vendor advisory: https://support.microsoft.com/help/5001999

## Applies to

| Product | Release | Fixed in |
|---|---|---|
| [Microsoft Office Online Server](https://patchblox.com/security/data/product/microsoft/microsoft-office-online-server.md) |  |  |

## CVEs this fix closes

| CVE | Priority | Component | CVSS | EPSS | Exploitation |
|---|---|---|---:|---:|---|
| [CVE-2021-38655](https://patchblox.com/security/data/cve/CVE-2021-38655.md) | High | Microsoft Office Excel | 7.8 | 0.0639 |  |

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Data as of 2026-11-07T18:46:35Z 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 Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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