Windows: Heap-based buffer overflow in Direct Composition enables privilege escalation

Summary

A heap-based buffer overflow (CWE-122) in the Windows Direct Composition graphics component allows privilege escalation on affected Windows 10, Windows 11 and Windows Server systems. An attacker needs local access and an authenticated low-privilege account or code execution on the machine. Successful exploitation could give the attacker higher privileges, with a CVSS 3.1 base score of 7.8 (High).

Affected

• Windows 10 Version 1809 and Windows Server 2019 (including Server Core): builds before 10.0.17763.9376
• 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 and 25H2, Windows 11 Version 26H2: builds before 10.0.26100.9711 / 10.0.26200.9711 / 10.0.26300.9711
• Windows 11 Version 26H1: builds before 10.0.28000.3231
• Windows Server 2022: builds before 10.0.20348.5761
• Windows Server 2025 (including Server Core): builds before 10.0.26100.33650

Fixed in

• Install the October 2026 Windows security update for your version (Microsoft Security Update Guide).
• Fixed builds are listed under 'affected' above, as stated in the CVE record. Verify them against the MSRC advisory before deployment.

Workaround

Unknown.

Exploitation

• No evidence of exploitation in the wild (CISA SSVC: Exploitation 'none').
• CISA SSVC: not automatable.
• No public proof of concept found in the sources checked; this is not proof that none exists.
• EPSS about 0.0036 (low exploitation probability estimate).

Our recommendation

• Apply the October 2026 Windows security update on all affected endpoints and servers as part of the normal Patch Tuesday cycle.
• Prioritise Windows 10 Version 1809 and Windows Server 2019 hosts that are still in use, and check their support status.
• Restrict local logon and limit standard user privileges where possible, as this vulnerability is a second stage after malware or phishing.
• Monitor endpoints for unexpected privilege changes and new processes running as SYSTEM.

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-2026-83902 msrc.microsoft.com
• Vulners: CVE-2026-83902 (CVE record mirror) vulners.com
• OpenCVE: CVE-2026-83902 app.opencve.io

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, 02:37.