3 OctRestore deleted or older files in OneDrive3 OctRun the Windows Update troubleshooter3 OctWindows File Recovery: recover permanently deleted files with winfr3 OctHow to update drivers in Windows 11 and 10 (roll back, reinstall)3 OctDisable Fast Startup in Windows 11 and 103 OctUse System Restore in Windows 11 and Windows 103 OctHow to stop apps from opening on startup3 OctRun Startup Repair in Windows 11 (fix the Automatic Repair loop)

KB5103212: what it fixes and who gets it

KB5103212 is a security update from Microsoft's July 2026 release for Microsoft Exchange Server Subscription Edition RTM.

Microsoft data read
4CVEs fixed
1rated Critical
0already exploited
Yesrestart required

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 KB5103212

CVETypeCVSSSeverity
CVE-2026-55008Microsoft Exchange Server Spoofing VulnerabilitySpoofing9.6Critical
CVE-2026-55005Microsoft Exchange Server Remote Code Execution VulnerabilityRemote Code Execution8.8Important
CVE-2026-55006Microsoft Exchange Server Elevation of Privilege VulnerabilityElevation of Privilege7.8Important
CVE-2026-55009Microsoft Exchange Server Elevation of Privilege VulnerabilityElevation of Privilege7.8Important

Questions and experiences

Ask about this page: members and our editors answer. Reading is open; writing needs a free account.

0 comments

…

4,322 members already hereThey read, write, comment and vote. 0 verified · 31 joined this year
All membersJoin

Cookies

We use essential cookies to run the platform. Analytics and marketing cookies are only turned on once you consent — you can change your choice at any time.