# KB5003729: May 2021 security update

KB5003729, released May 11, 2021, fixes 2 CVEs across 3 products. 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/kb5003729
- Platform: Microsoft
- Released: May 11, 2021
- Priority: High (Closes CVE-2021-26422, high severity)
- CVEs: 2, exploited: 0, on CISA KEV: 0
- Vendor advisory: https://support.microsoft.com/help/5003729

## Applies to

| Product | Release | Fixed in |
|---|---|---|
| [Microsoft Lync Server 2013 CU10](https://patchblox.com/security/data/product/microsoft/microsoft-lync-server-2013-cu10.md) |  |  |
| [Skype for Business Server 2015 CU11](https://patchblox.com/security/data/product/microsoft/skype-for-business-server-2015-cu11.md) |  |  |
| [Skype for Business Server 2019 CU5](https://patchblox.com/security/data/product/microsoft/skype-for-business-server-2019-cu5.md) |  |  |

## CVEs this fix closes

| CVE | Priority | Component | CVSS | EPSS | Exploitation |
|---|---|---|---:|---:|---|
| [CVE-2021-26422](https://patchblox.com/security/data/cve/CVE-2021-26422.md) | High | Skype for Business and Microsoft Lync | 7.2 | 0.0222 |  |
| [CVE-2021-26421](https://patchblox.com/security/data/cve/CVE-2021-26421.md) | Routine | Skype for Business and Microsoft Lync | 6.5 | 0.0141 |  |

---

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 Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo