CVE-2026-62871
High CVSS 7.8Published 2026-08-11 ยท last changed 2026-08-13
The fix
Microsoft fixes this in updatesKB5122104, KB5122105. 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 8.0 installed on Windows | 8.0.30 | KB5122104 | 2026-09-20 |
| .NET 9.0 installed on Windows | 9.0.19 | KB5122105 | 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
Out-of-bounds write in .NET allows an unauthorized attacker to execute code locally.
Sources
CVSS vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H