Windows NetBIOS: Heap-based buffer overflow allows privilege escalation

Summary

A heap-based buffer overflow in the Windows NetBIOS component allows an attacker to elevate privileges on affected Windows 10, Windows 11 and Windows Server systems. The official record scores the flaw as network-reachable with user interaction required, but a related Microsoft advisory (CVE-2026-70054) is scored as local with low privileges, so the actual attack path is still unclear. Microsoft's exploit maturity rating is Unproven and no exploitation in the wild is known.

Affected

• Windows 10 Version 1607 before 10.0.14393.9688 - Windows 10 Version 1809 before 10.0.17763.9487 - Windows 10 Version 21H2 before 10.0.19044.7846 - Windows 10 Version 22H2 before 10.0.19045.7846 - Windows 11 Version 23H2 before 10.0.22631.7711 - Windows 11 Version 24H2 before 10.0.26100.9974 - Windows 11 Version 25H2 before 10.0.26200.9974 - Windows 11 Version 26H1 before 10.0.28000.3501 - Windows 11 Version 26H2 before 10.0.26300.9974 - Windows Server 2016 (including Server Core) before 10.0.14393.9688 - Windows Server 2019 (including Server Core) before 10.0.17763.9487 - Windows Server 2022 before 10.0.20348.5870 - Windows Server 2025: Unknown, only a third-party source lists it.

Fixed in

• Install the Microsoft security update for CVE-2026-105551 that brings the builds above to at least the listed fixed version. Check the MSRC advisory for the exact KB articles.

Workaround

• No workaround is documented by Microsoft. Where NetBIOS over TCP/IP is not required, disable it on network adapters. Block NetBIOS ports (TCP 139, UDP 137 and 138, and TCP 445 where SMB is not needed) at the perimeter and between network segments.

Exploitation

• Not known to be exploited in the wild according to a secondary source. The CISA KEV catalog has not been checked directly. Microsoft's CVSS temporal vector uses E:U (exploit code maturity Unproven). No public proof of concept has been found, but the CVE was published only on 2026-11-10.

Our recommendation

• Inventory Windows 10 and Windows Server systems with NetBIOS enabled and compare their build numbers with the list above. Prioritise unpatched Windows 10 1607, 1809 and 21H2 systems and any unsupported Windows versions. Install the update within the normal patch cycle and disable NetBIOS where it is not required. Monitor for exploitation and check the MSRC advisory and NVD once the vector is confirmed.

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-2026-105551 msrc.microsoft.com
• CVE Record CVE-2026-105551 www.cve.org
• Strix: CVE-2026-105551 www.strix.ai
• Microsoft Security Update Guide: CVE-2026-70054 (related NetBIOS advisory) msrc.microsoft.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, 06:11.