Microsoft Windows: Use after free in Secure Kernel Mode enables privilege escalation

Summary

A use-after-free flaw (CWE-416) in Windows Secure Kernel Mode allows an authorized local attacker to elevate privileges. The attacker needs an existing low-privilege account or foothold on the system, so the flaw cannot be reached from outside the network. It matters most after phishing, a malicious application or a compromised user account. NVD lists a CVSS 3.1 base score of 7.0, but this score is unverified; an independent calculation gives 6.4.

Affected

• Windows 10 Version 1809 and Windows Server 2019 (including Server Core): before 10.0.17763.9376
• Windows 10 Version 21H2: before 10.0.19044.7807
• Windows 10 Version 22H2: before 10.0.19045.7807
• Windows 11 Version 23H2: before 10.0.22631.7652
• Windows 11 Version 24H2: before 10.0.26100.9711
• Windows 11 Version 25H2: before 10.0.26200.9711
• Windows 11 Version 26H1: before 10.0.28000.3231
• Windows 11 Version 26H2: before 10.0.26300.9711
• Windows Server 2022: before 10.0.20348.5761
• Windows Server 2025 (including Server Core): before 10.0.26100.33650

Fixed in

• Windows 10 Version 1809 and Windows Server 2019: build 10.0.17763.9376 or later (KB5126651, October 2026 security update)
• Windows Server 2025: build 10.0.26100.33650 or later (KB5126646, October 2026 security update)
• Other listed versions: fixed in the October 2026 Windows updates, build numbers as listed under Affected. KB numbers for these versions are unconfirmed.

Workaround

Unknown.

• No vendor workaround was identified. Installing the security update is the fix.

Exploitation

• No evidence of exploitation in the wild found.
• Not listed in the CISA KEV catalog in the sources checked.
• No public proof-of-concept exploit found.
• EPSS score is low (0.00264).
• CISA SSVC: exploitation none, automatable no, technical impact total.

Our recommendation

• Install the October 2026 Windows security updates, starting with multi-user servers, Remote Desktop hosts and machines with shared or untrusted users.
• Check the exact build numbers against the MSRC advisory before rollout.
• Verify that all systems are still supported by Microsoft; unsupported systems such as Windows 10 Version 1809 or Server 2019 past end of service must be upgraded, because they will not receive this fix.
• Restrict local logon rights and monitor for unexpected privilege changes and disabled security tools.
• Priority: medium, within the normal patch cycle.

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-2026-70026 msrc.microsoft.com
• NVD record mirror (Vulners) vulners.com
• CNA affected-version data (Vulners CVELIST) vulners.com
• Microsoft advisory mirror (Vulners MSCVE) vulners.com
• Description and references (OpenCVE) app.opencve.io
• EPSS and KEV watch-list entry (GitHub) github.com

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 4 Nov 2026, 09:25.