Windows Direct Composition: Heap buffer overflow allows local privilege escalation
Summary
A heap-based buffer overflow in the Windows Direct Composition graphics component allows an authorized local user to elevate privileges. An attacker needs a low-privileged account or code running on the affected system, for example after phishing or malware running as a standard user. Successful exploitation can give full control over confidentiality, integrity and availability.
Affected
- 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 26H2: 10.0.26300.0 to before 10.0.26300.9711
- Windows Server 2025 (including Server Core): 10.0.26100.0 to before 10.0.26100.33650
Fixed in
- Windows 11 24H2: build 10.0.26100.9711 or later
- Windows 11 25H2: build 10.0.26200.9711 or later
- Windows 11 26H2: build 10.0.26300.9711 or later
- Windows Server 2025: build 10.0.26100.33650 or later
- Patch: October 2026 security update (a third-party listing names KB5127648; verify on the MSRC page)
Workaround
Unknown. No workaround is documented in the sources reviewed. Patching is the remedy.
Exploitation
- Not listed in the CISA Known Exploited Vulnerabilities catalog.
- CISA SSVC: Exploitation none, Automatable no, Technical Impact total.
- No public proof of concept found in the sources reviewed.
Our recommendation
- Install the October 2026 security update or later on all Windows 11 24H2, 25H2 and 26H2 and Windows Server 2025 systems.
- Prioritise shared workstations, RDS/terminal servers and systems where users run untrusted software.
- Check the MSRC advisory for the exact KB number and fixed builds before rollout.
- Monitor for unusual privilege changes or new SYSTEM processes on endpoints.
Information from Microsoft (Patch Tuesday October 2026)
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Microsoft Security Update Guide: CVE-2026-83903 msrc.microsoft.com
- Vulners: CVE List record CVE-2026-83903 vulners.com
- Vulners: NVD record CVE-2026-83903 vulners.com
- OpenCVE: CVE-2026-83903 app.opencve.io
- Patch Tuesday coverage (Anoop C. Nair) www.anoopcnair.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, 02:37.
Original description (NVD)
Heap-based buffer overflow in Windows Direct Composition allows an authorized attacker to elevate privileges locally.
NVD references (1)
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
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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