KB5122105: what it fixes and who gets it
KB5122105 is a security update from Microsoft's August 2026 release for .NET 9.0 installed on Linux, .NET 9.0 installed on Mac OS, .NET 9.0 installed on Windows.
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Should you install it?
Yes. It is a routine security update; none of its fixes are rated Critical or reported as exploited. 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 KB5122105
| CVE | Type | CVSS | Severity |
|---|---|---|---|
| CVE-2026-62871.NET Elevation of Privilege Vulnerability | Remote Code Execution | 7.8 | Important |
| CVE-2026-62886.NET Elevation of Privilege Vulnerability | Elevation of Privilege | 7.8 | Important |
| CVE-2026-62909.NET Elevation of Privilege Vulnerability | Elevation of Privilege | 7.8 | Important |
| CVE-2026-70354.NET Core Remote Code Execution Vulnerability | Remote Code Execution | 7.8 | Important |
| CVE-2026-62898Microsoft QUIC Information Disclosure Vulnerability | Information Disclosure | 7.5 | Important |
| CVE-2026-62901.NET Denial of Service Vulnerability | Denial of Service | 7.5 | Important |
| CVE-2026-62897.NET Framework Remote Code Execution Vulnerability | Remote Code Execution | 7.0 | Important |
| CVE-2026-62902.NET Information Disclosure Vulnerability | Information Disclosure | 6.5 | Important |
| CVE-2026-62899.NET Security Feature Bypass Vulnerability | Security Feature Bypass | 5.9 | Important |
| CVE-2026-62900.NET Information Disclosure Vulnerability | Information Disclosure | 5.9 | Important |
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