KB5121576: what it fixes and who gets it
KB5121576 is a security update from Microsoft's August 2026 release for Microsoft Exchange Server 2016 Cumulative Update 23.
Microsoft data read
Should you install it?
Yes. It closes holes Microsoft rates Critical, the most serious rating it uses. Windows Update installs it automatically on supported home PCs.
If the installation fails or the PC misbehaves afterwards, note the exact error code first: the fix depends on it. Our update troubleshooting guides are linked on this page.
Security fixes in KB5121576
| CVE | Type | CVSS | Severity |
|---|---|---|---|
| CVE-2026-62911Microsoft Exchange Server Elevation of Privilege Vulnerability | Elevation of Privilege | 8.0 | Critical |
| CVE-2026-62913Microsoft Exchange Server Remote Code Execution Vulnerability | Remote Code Execution | 8.8 | Important |
| CVE-2026-62914Microsoft Exchange Server Spoofing Vulnerability | Spoofing | 7.3 | Important |
| CVE-2026-62910Microsoft Exchange Server Elevation of Privilege Vulnerability | Elevation of Privilege | 7.2 | Important |
| CVE-2026-62912Microsoft Exchange Server Denial of Service Vulnerability | Denial of Service | 6.5 | Important |
| CVE-2026-62915Microsoft Exchange Server Security Feature Bypass Vulnerability | Security Feature Bypass | 6.5 | Important |
| CVE-2026-65813Microsoft Exchange Server Elevation of Privilege Vulnerability | Elevation of Privilege | 6.5 | Important |
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