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Microsoft Windows LSASS: Remote code execution via out-of-bounds write

CVE-2026-96219Critical 9.8

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Summary

A critical out-of-bounds write in the Windows Local Security Authority Subsystem Service (LSASS) allows an unauthenticated remote attacker to execute code over a network. LSASS handles authentication and security policy, so a compromise on a domain controller or server could give an attacker control of the Windows domain. Microsoft and NVD rate the flaw 9.8 (CVSS 3.1). The network service or protocol that triggers the flaw is not stated in the sources reviewed.

Affected

  • Windows 10 Version 1809 and Windows Server 2019 (including Server Core): 10.0.17763.0 to before 10.0.17763.9376
  • Windows 10 Version 21H2: 10.0.19044.0 to before 10.0.19044.7807
  • Windows 10 Version 22H2: 10.0.19045.0 to before 10.0.19045.7807
  • Windows 11 Version 23H2: 10.0.22631.0 to before 10.0.22631.7652
  • Windows 11 Version 24H2: 10.0.26100.0 to before 10.0.26100.9711
  • Windows 11 Version 25H2: 10.0.26200.0 to before 10.0.26200.9711
  • Windows 11 Version 26H1: 10.0.28000.0 to before 10.0.28000.3231
  • Windows 11 Version 26H2: 10.0.26300.0 to before 10.0.26300.9711
  • Windows Server 2022: 10.0.20348.0 to before 10.0.20348.5761
  • Windows Server 2025 (including Server Core): 10.0.26100.0 to before 10.0.26100.33650
  • Note: NVD lists only Windows 10 1809 in its CPE data; the MSRC table should be checked for the complete list.

Fixed in

  • Apply the October 2026 Microsoft security update for your Windows version.
  • Windows 10 Version 1809 / Server 2019: 10.0.17763.9376 (unverified, third-party source)
  • Windows 10 Version 21H2: October 2026 update per KB article 5126657 (exact build unverified)
  • Other versions: see the fixed builds listed in the MSRC advisory.

Workaround

  • None published in the sources reviewed.

Exploitation

  • CISA SSVC: exploitation none; the automatable value conflicts between sources.
  • Not listed in CISA KEV.
  • No public proof of concept found.
  • No reports of exploitation in the wild found; confidence moderate, as searches were limited.

Our recommendation

  • Confirm affected and fixed builds in the MSRC advisory before rollout.
  • Patch domain controllers and internet-facing servers first, then all other Windows systems.
  • Check whether any Windows 10 1809 hosts are still in support; upgrade unsupported systems instead of only patching them.
  • Review network exposure of LSASS-related services and monitor MSRC and CISA for changes in exploitation status.

Information from Microsoft (Patch Tuesday October 2026)

Severity (Microsoft)
Important
Impact
Remote code execution – Windows Local Security Authority Subsystem Service (LSASS)
Status on Patch Tuesday
Neither exploited nor publicly disclosed
Exploitability assessment
Exploitation less likely
Product family
Windows, Windows ESU (Extended Security Updates)
Updates (KB)
KB5127646, KB5126651, KB5126657, KB5126655, KB5126653, KB5127648

Entry in the Microsoft Security Update Guide

Public exploits

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

Research sources

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 30 Oct 2026, 18:18.

Original description (NVD)

Out-of-bounds write in Windows Local Security Authority Subsystem Service (LSASS) allows an unauthorized attacker to execute code over a network.

NVD references (1)

Sources

The tracker combines official, freely usable data sources – updated continuously:

This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.

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