# CVE-2021-26421: Skype for Business and Lync Spoofing Vulnerability

CVE-2021-26421 is fixed in 2 products on 1 platform, first by KB5003729, released May 11, 2021. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2021-26421
- Priority: Routine
- CVSS: 6.5 (Important)
- EPSS: 0.0141
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Vendor exploitability assessment: Exploitation Less Likely
- Published: May 11, 2021
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-26421

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Microsoft | Microsoft Lync Server 2013 CU10 |  | [KB5003729](https://patchblox.com/security/data/fix/microsoft/kb5003729.md) | May 11, 2021 |
| Microsoft | Skype for Business Server 2015 CU11 |  | [KB5003729](https://patchblox.com/security/data/fix/microsoft/kb5003729.md) | May 11, 2021 |

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Data as of 2026-11-08T06:59:42Z 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 Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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