Microsoft Windows: Heap-based buffer overflow in Windows Update Service

Summary

A heap-based buffer overflow in the Windows Update Service allows an authorized local user to elevate privileges on affected Windows 10, Windows 11 and Windows Server systems. The attacker needs an existing low-privileged session or code execution on the machine; no remote attack path is described. Successful exploitation can lead to full compromise of confidentiality, integrity and availability.

Affected

• Windows 10 Version 1607 (10.0.14393.0 before 10.0.14393.9612)
• Windows 10 Version 1809 (10.0.17763.0 before 10.0.17763.9376)
• Windows 10 Version 21H2 and 22H2 (10.0.19044.0 and 10.0.19045.0 before 10.0.19044.7807 / 10.0.19045.7807)
• Windows 11 Version 23H2 (10.0.22631.0 before 10.0.22631.7652)
• Windows 11 Version 24H2, 25H2 and 26H2 (before 10.0.26100.9711, 10.0.26200.9711, 10.0.26300.9711)
• Windows 11 Version 26H1 (10.0.28000.0 before 10.0.28000.3231)
• Windows Server 2012 and 2012 R2, including Server Core (before 6.2.9200.26434 and 6.3.9600.23470)
• Windows Server 2016 (10.0.14393.0 before 10.0.14393.9612)
• The CPE entry lists only Windows 10 1607; the CNA record lists the broader set above.

Fixed in

• Windows 10 1607 and Windows Server 2016: build 10.0.14393.9612 or later
• Windows 10 1809: build 10.0.17763.9376 or later
• Windows 10 21H2 and 22H2: build 10.0.19044.7807 or 10.0.19045.7807 or later
• Windows 11 23H2: build 10.0.22631.7652 or later
• Windows 11 24H2, 25H2, 26H2: build 10.0.26100.9711, 10.0.26200.9711 or 10.0.26300.9711 or later
• Windows 11 26H1: build 10.0.28000.3231 or later
• Windows Server 2012 / 2012 R2: build 6.2.9200.26434 / 6.3.9600.23470 or later
• KB numbers: Unknown for Windows 10 1607; KB5126646 (Server 2025) and KB5126651 (Windows 10 1809 / Server 2019) per third-party listing. Verify on MSRC.

Workaround

Unknown. No vendor-stated workaround is confirmed.

• General hardening: restrict local administrator rights and enforce least privilege.

Exploitation

• CISA SSVC: exploitation none, automatable no, technical impact total.
• No evidence of exploitation in the wild; not listed in CISA KEV (per OpenCVE).
• No public proof of concept found in the research.
• EPSS about 0.3 % (0.00341 to 0.00379).

Our recommendation

• Install the October 2026 Microsoft security update on all affected Windows systems, starting with shared workstations and terminal servers.
• Confirm the Windows 10 1607 fixed build and KB number on MSRC, and check whether the device is still supported or covered by ESU, since an unsupported build may receive no fix.
• Make sure WSUS or Intune does not block the October release.
• Restrict local administrator rights and monitor for unexpected privilege changes.

Public exploits iAttack code is publicly available (PoC on GitHub, Metasploit or Exploit-DB).

PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.

Research sources

• Microsoft Security Update Guide: CVE-2026-70139 msrc.microsoft.com
• Vulners: NVD record CVE-2026-70139 vulners.com
• OpenCVE: CVE-2026-70139 app.opencve.io
• VulDB: CVE-2026-70139 vuldb.com
• Strix: CVE-2026-70139 (third-party aggregator) www.strix.ai

Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 2 Nov 2026, 04:06.