CVE-2026-69439
High CVSS 8.8Published 2026-09-08 ยท last changed 2026-09-09
The fix
Microsoft fixes this in updatesKB5126106, KB5126104, KB5126105. The fixed build differs per Windows version, so the row that matters is the one matching the machine you are looking at.
| Windows version | Fixed in build | Update | Released |
|---|---|---|---|
| .NET 10.0 installed on Windows | 10.0.12 | KB5126106 | 2026-09-20 |
| .NET 11.0 installed on Windows | 11.0 RC1 | configuration change | 2026-09-20 |
| .NET 8.0 installed on Windows | 8.0.31 | KB5126104 | 2026-09-20 |
| .NET 9.0 installed on Windows | 9.0.20 | KB5126105 | 2026-09-20 |
Having the KB is not the same as knowing whether a machine has it. Windows updates supersede each other, so the update you installed often covers a fix that shipped in an earlier one. Paste your build into the patch checker and it walks that chain for you.
What it is
Heap-based buffer overflow in .NET and Visual Studio allows an unauthorized attacker to elevate privileges over a network.
Sources
CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H