What is CVE-2026-42904?

CVE-2026-42904 is a critical-severity vulnerability in Microsoft Windows_10_21h2, classified under Heap-based Buffer Overflow. CVSS score: 9.6/10. Published 2026-06-09.

How severe is CVE-2026-42904?

Critical severity. CVSS v3 base score is 9.6 out of 10.

Buffer overflow in Microsoft Windows_10_21h2

CVE-2026-42904

Heap-based buffer overflow in Windows TCP/IP allows an unauthorized attacker to elevate privileges over an adjacent network.

Vulnerability class: Buffer Overflow

CVSS v3 metric

CVSS v3 base score 9.6 (Critical). Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H.

Affected products

Microsoft Windows_10_21h2
Microsoft Windows_10_22h2
Microsoft Windows_11_23h2
Microsoft Windows_11_24h2
Microsoft Windows_11_25h2
Microsoft Windows_11_26h1
Microsoft Windows_server_2022
Microsoft Windows_server_2025

Weakness classification (CWE)

CWE-122 — Heap-based Buffer Overflow

References

secure@microsoft.com (Vendor Advisory)

Frequently asked questions

What is CVE-2026-42904?: CVE-2026-42904 is a critical-severity vulnerability in Microsoft Windows_10_21h2, classified under Heap-based Buffer Overflow. CVSS score: 9.6/10. Published 2026-06-09.
How severe is CVE-2026-42904?: Critical severity. CVSS v3 base score is 9.6 out of 10.