Patch tracker / KB5123303
KB5123303: Windows Server 2019 Security Update (August 2026)
KB5123303 is a High security update for Windows Server 2019, released 2026-08-11. It closes 3 CVEs with a maximum CVSS of 7.9. The most likely of them to be attacked is CVE-2026-66799, which FIRST.org rates at 6% probability of exploitation in the next 30 days.
Update summary
Fixes 3 CVEs. Most severe CVSS 7.9 (High). EPSS exploit probability up to <1%. Among the lower half of tracked Microsoft updates by EPSS exploit probability.
Microsoft documents 1 known issue with this update.
- Microsoft is not currently aware of any issues with this update.
Senserva AI Opinion and rich prompt for KB5123303
Copy this prompt into Claude, ChatGPT, or Copilot. The facts are included, sourced from this page.
Full tracking and change history for KB5123303
- Released
- 2026-08-11
- Last changed
- 2026-08-11
- Changes tracked
- 1
Senserva began recording day-to-day change history on 2026-07-07, and refreshes it several times a day. Release dates are historical where Microsoft publishes them; revision history is tracked from that date forward, so it does not include changes made before then.
Check if KB5123303 is installed
Elevated PowerShell. No output means it is not installed.
Known issues, from Microsoft
Quoted from Microsoft's support article for KB5123303 (checked 2026-08-26). Verify against the article before acting.
Microsoft is not currently aware of any issues with this update.
CVEs fixed by this update
Sorted exploited-first, then by CVSS. Every CVE links to its Senserva page with the full risk facts, references, and a ready-to-paste AI prompt.
| CVE | Severity | CVSS | EPSS | Exploited |
|---|---|---|---|---|
| CVE-2026-6726 | High | 7.9 | 6.2% | No |
| CVE-2026-66799 | High | 7.8 | 6.2% | No |
| CVE-2026-6727 | Medium | 5.9 | 6.2% | No |
What the press says about this update
Trusted-source coverage of the CVEs this update fixes, pulled live from their own feeds.
Scope and sources
- Affected products
- Also released in August 2026
KB5002882
39 CVEs · Critical · exploitedKB5002883
40 CVEs · Critical · exploitedKB5002891
40 CVEs · Critical · exploitedKB5120228
215 CVEs · Critical · exploitedKB5120229
195 CVEs · Critical · exploitedKB5120233
215 CVEs · Critical · exploitedKB5120238
183 CVEs · Critical · exploitedKB5120240
171 CVEs · Critical · exploitedThe full month, summarized: Microsoft Patch Tuesday.
- Authoritative references
See this and every Microsoft update ranked by real-world risk on the Microsoft Patch Tracker.