Microsoft Windows: Local privilege escalation in Microsoft Account Sign-in Assistant

Summary

A heap-based buffer overflow in the Windows Microsoft Account Sign-in Assistant service allows a local attacker to elevate privileges. The attacker needs a valid local account with low privileges, and no user interaction is required. The flaw is not remotely exploitable, but it can give an attacker who already runs code on a system full control over it.

Affected

• Windows 10 Version 1607 and Windows Server 2016 (including Server Core): 10.0.14393.0 to before 10.0.14393.9688
• Windows 10 Version 1809 and Windows Server 2019 (including Server Core): 10.0.17763.0 to before 10.0.17763.9487
• Windows 10 Version 21H2: 10.0.19044.0 to before 10.0.19044.7846
• Windows 10 Version 22H2: 10.0.19045.0 to before 10.0.19045.7846
• Windows 11 Version 23H2: 10.0.22631.0 to before 10.0.22631.7711
• Windows 11 Version 24H2: 10.0.26100.0 to before 10.0.26100.9974
• Windows 11 Version 25H2: 10.0.26200.0 to before 10.0.26200.9974
• Windows 11 Version 26H1: 10.0.28000.0 to before 10.0.28000.3501
• Windows 11 Version 26H2: 10.0.26300.0 to before 10.0.26300.9974
• Windows Server 2022: 10.0.20348.0 to before 10.0.20348.5870

Fixed in

• Fixed in the November 2026 security update.
• Fixed builds per the vendor record: 10.0.14393.9688 or later (Windows 10 1607, Server 2016); 10.0.17763.9487 or later (Windows 10 1809, Server 2019); 10.0.19044.7846 or later (Windows 10 21H2); 10.0.19045.7846 or later (Windows 10 22H2); 10.0.22631.7711 or later (Windows 11 23H2); 10.0.26100.9974 or later (Windows 11 24H2); 10.0.26200.9974 or later (Windows 11 25H2); 10.0.28000.3501 or later (Windows 11 26H1); 10.0.26300.9974 or later (Windows 11 26H2); 10.0.20348.5870 or later (Windows Server 2022).
• Confirm the knowledge base (KB) article per build in the Microsoft advisory; this could not be verified.

Workaround

Unknown.

• No Microsoft-documented workaround was found. Applying the security update is the recommended fix.

Exploitation

• No evidence of exploitation in the wild was found.
• No public proof-of-concept exploit was found.
• CISA SSVC assessment: exploitation none, not automatable, total technical impact.
• Not listed in the CISA Known Exploited Vulnerabilities catalog at the time of research.

Our recommendation

• Install the November 2026 security update on all affected Windows 10, Windows 11 and Windows Server systems.
• Prioritise shared PCs, terminal servers and systems where users have local accounts.
• Check whether any Windows 10 builds still in use are still supported.
• Monitor the Microsoft advisory and the CISA catalog for changes, as this CVE is recent and under analysis.

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-2026-119816 msrc.microsoft.com
• CVE Record CVE-2026-119816 (CVE Program) www.cve.org
• VulDB entry 434145 vuldb.com
• Senserva KB 5132061 (Windows 11 24H2 November 2026 update) senserva.com
• Talos: Microsoft Patch Tuesday for November 2026 blog.talosintelligence.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 11 Nov 2026, 03:51.