# KB5123300: September 2026 security update

KB5123300, released September 8, 2026, fixes 10 CVEs across 2 products. None of them is reported as exploited. Patch Radar priority: Urgent.

- Web page: https://patchblox.com/security/fix/microsoft/kb5123300
- Platform: Microsoft
- Released: Sep 8, 2026
- Priority: Urgent (Closes CVE-2026-66302, rated Critical)
- CVEs: 10, exploited: 0, on CISA KEV: 0
- Vendor advisory: https://support.microsoft.com/help/5123300

## Applies to

| Product | Release | Fixed in |
|---|---|---|
| [Skype for Business Server 2019 CU8](https://patchblox.com/security/data/product/microsoft/skype-for-business-server-2019-cu8.md) |  |  |
| [Skype for Business Server Subscription Edition CU1](https://patchblox.com/security/data/product/microsoft/skype-for-business-server-subscription-edition-cu1.md) |  |  |

## CVEs this fix closes

| CVE | Priority | Component | CVSS | EPSS | Exploitation |
|---|---|---|---:|---:|---|
| [CVE-2026-66302](https://patchblox.com/security/data/cve/CVE-2026-66302.md) | Urgent | Skype for Business | 9.8 | 0.0097 |  |
| [CVE-2026-66307](https://patchblox.com/security/data/cve/CVE-2026-66307.md) | High | Skype for Business | 7.5 | 0.0117 |  |
| [CVE-2026-66304](https://patchblox.com/security/data/cve/CVE-2026-66304.md) | High | Skype for Business | 7.5 | 0.0097 |  |
| [CVE-2026-66305](https://patchblox.com/security/data/cve/CVE-2026-66305.md) | High | Skype for Business | 7.1 | 0.0053 |  |
| [CVE-2026-69646](https://patchblox.com/security/data/cve/CVE-2026-69646.md) | High | Skype for Business | 8.3 | 0.0032 |  |
| [CVE-2026-66303](https://patchblox.com/security/data/cve/CVE-2026-66303.md) | Routine | Skype for Business | 6.5 | 0.0114 |  |
| [CVE-2026-66308](https://patchblox.com/security/data/cve/CVE-2026-66308.md) | Routine | Skype for Business | 6.5 | 0.0114 |  |
| [CVE-2026-66306](https://patchblox.com/security/data/cve/CVE-2026-66306.md) | Routine | Skype for Business | 6.5 | 0.0092 |  |
| [CVE-2026-63523](https://patchblox.com/security/data/cve/CVE-2026-63523.md) | Routine | Skype for Business | 6.5 | 0.0055 |  |
| [CVE-2026-69642](https://patchblox.com/security/data/cve/CVE-2026-69642.md) | Routine | Skype for Business | 6.5 | 0.0041 |  |

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 Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo