KB5128896: what it fixes and who gets it
KB5128896 is a security update from Microsoft's October 2026 release for Microsoft Exchange Server 2019 Cumulative Update 15.
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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 KB5128896
| CVE | Type | CVSS | Severity |
|---|---|---|---|
| CVE-2026-70571Microsoft Exchange Server Remote Code Execution Vulnerability | Remote Code Execution | 8.1 | Critical |
| CVE-2026-70279Microsoft Exchange Server Spoofing Vulnerability | Spoofing | 9.3 | Important |
| CVE-2026-77910Microsoft Exchange Server Elevation of Privilege Vulnerability | Elevation of Privilege | 8.8 | Important |
| CVE-2026-87695Microsoft Exchange Server Elevation of Privilege Vulnerability | Elevation of Privilege | 7.8 | Important |
| CVE-2026-87696Microsoft Exchange Server Elevation of Privilege Vulnerability | Elevation of Privilege | 7.5 | Important |
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