# KB4504721: April 2021 security update

KB4504721, released April 13, 2021, fixes 4 CVEs across 2 products. None of them is reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/fix/microsoft/kb4504721
- Platform: Microsoft
- Released: Apr 13, 2021
- Priority: High (Closes CVE-2021-28454, high severity)
- CVEs: 4, exploited: 0, on CISA KEV: 0
- Vendor advisory: https://support.microsoft.com/help/4504721

## Applies to

| Product | Release | Fixed in |
|---|---|---|
| [Microsoft Excel 2016 (32-bit edition)](https://patchblox.com/security/data/product/microsoft/microsoft-excel-2016-32-bit-edition.md) |  |  |
| [Microsoft Excel 2016 (64-bit edition)](https://patchblox.com/security/data/product/microsoft/microsoft-excel-2016-64-bit-edition.md) |  |  |

## CVEs this fix closes

| CVE | Priority | Component | CVSS | EPSS | Exploitation |
|---|---|---|---:|---:|---|
| [CVE-2021-28454](https://patchblox.com/security/data/cve/CVE-2021-28454.md) | High | Microsoft Office Excel | 7.8 | 0.0335 |  |
| [CVE-2021-28449](https://patchblox.com/security/data/cve/CVE-2021-28449.md) | High | Microsoft Office Excel | 7.8 | 0.0269 |  |
| [CVE-2021-28451](https://patchblox.com/security/data/cve/CVE-2021-28451.md) | High | Microsoft Office Excel | 7.8 | 0.0250 |  |
| [CVE-2021-28456](https://patchblox.com/security/data/cve/CVE-2021-28456.md) | Routine | Microsoft Office Excel | 5.5 | 0.0367 |  |

---

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 Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo