Microsoft Windows: Heap overflow in Direct Composition allows privilege escalation

Summary

A heap-based buffer overflow in the Windows Direct Composition component allows an attacker with a low-privileged local account to elevate privileges to a higher level. Successful exploitation would give the attacker high impact on confidentiality, integrity and availability of the affected system. The vulnerability is not reachable from the internet and requires a foothold on the system first, for example via phishing or malware.

Affected

• Windows 10 Version 1607 (builds before 10.0.14393.9612), including Windows Server 2016 and Server Core installations
• Windows 10 Version 1809 (builds before 10.0.17763.9376) and Windows Server 2019, including Server Core
• Windows 10 Version 21H2 (builds before 10.0.19044.7807)
• Windows 10 Version 22H2 (builds before 10.0.19045.7807)
• Windows 11 Version 23H2 (builds before 10.0.22631.7652)
• Windows 11 Version 24H2 (builds before 10.0.26100.9711)
• Windows 11 Version 25H2 (builds before 10.0.26200.9711)
• Windows 11 Version 26H1 (builds before 10.0.28000.3231)
• Windows 11 Version 26H2 (builds before 10.0.26300.9711)
• Windows Server 2022 (builds before 10.0.20348.5761)

Fixed in

• Windows 10 1607 and Windows Server 2016: 10.0.14393.9612 (per CVE record; verify against the MSRC page)
• Windows 10 1809 and Windows Server 2019: 10.0.17763.9376
• Windows 10 21H2: 10.0.19044.7807
• Windows 10 22H2: 10.0.19045.7807
• Windows 11 23H2: 10.0.22631.7652
• Windows 11 24H2: 10.0.26100.9711
• Windows 11 25H2: 10.0.26200.9711
• Windows 11 26H1: 10.0.28000.3231
• Windows 11 26H2: 10.0.26300.9711
• Windows Server 2022: 10.0.20348.5761
• Knowledge base article numbers: unknown for Windows 10 1607 and 22H2; KB5126651 (Windows 10 1809 / Server 2019) reported by a third party, not verified.

Workaround

Unknown. No vendor workaround or mitigation was found.

Exploitation

• Not known to be exploited in the wild.
• Microsoft rates exploit maturity as Unproven at publication.
• CISA SSVC: exploitation none, automatable no, technical impact total.
• No public proof of concept was found; this does not prove that none exists.

Our recommendation

• Install the October 2026 security update on all affected systems, prioritising multi-user systems, terminal servers and servers where local users can log on.
• Check whether any Windows 10 1607 or Windows Server 2016 systems are still in use and whether they are still supported by Microsoft; verify this on the Microsoft lifecycle page. Upgrade or isolate unsupported systems.
• Verify the exact fixed builds and knowledge base articles on the MSRC page before rollout.
• Monitor for unusual local privilege changes and new administrative accounts.

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-2026-85902 msrc.microsoft.com
• Talos: Microsoft Patch Tuesday for October 2026 blog.talosintelligence.com
• OpenCVE: CVE-2026-85902 app.opencve.io
• VulDB: CVE-2026-85902 vuldb.com
• Vulners: NVD record CVE-2026-85902 vulners.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 2 Nov 2026, 01:48.