Microsoft Windows RDP: Heap-based buffer overflow enables local privilege escalation

Summary

A heap-based buffer overflow in the Windows Remote Desktop Protocol (RDP) component allows an authorized attacker with low privileges to elevate privileges to a higher level on the local system. Exploitation requires local access and a valid low-privileged account, and there is no user interaction. The vulnerability is not remotely exploitable, but an attacker who already has a foothold on a device (for example through a phished account or exposed RDP login) could gain full control of it.

Affected

• Windows 10 Version 1607 (10.0.14393.0 to before 10.0.14393.9612)
• Windows 10 Version 1809 (10.0.17763.0 to before 10.0.17763.9376)
• Windows 10 Version 21H2 (10.0.19044.0 to before 10.0.19044.7807)
• Windows 10 Version 22H2 (10.0.19045.0 to before 10.0.19045.7807)
• Windows 11 Version 23H2 (10.0.22631.0 to before 10.0.22631.7652)
• 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 26H1 (10.0.28000.0 to before 10.0.28000.3231)
• Windows 11 Version 26H2 (10.0.26300.0 to before 10.0.26300.9711)
• Windows Server 2012 incl. Server Core (6.2.9200.0 to before 6.2.9200.26434)
• Windows Server 2012 R2 incl. Server Core (6.3.9600.0 to before 6.3.9600.23470)
• Windows Server 2016 (10.0.14393.0 to before 10.0.14393.9612)

Fixed in

• Windows 10 1607 / Server 2016: 10.0.14393.9612
• Windows 10 1809: 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, 25H2, 26H2: 10.0.26100.9711 / 10.0.26200.9711 / 10.0.26300.9711
• Windows 11 26H1: 10.0.28000.3231
• Windows Server 2012: 6.2.9200.26434
• Windows Server 2012 R2: 6.3.9600.23470
• Fixed in the October 2026 security update cycle. Verify exact KB numbers in the MSRC Security Update Guide.

Workaround

Unknown. Microsoft has not confirmed a specific mitigation in the sources reviewed.

• Restrict Remote Desktop Services to authorized users and trusted IP addresses or VPN ranges (recommendation from a third-party source, not verified against MSRC).

Exploitation

• CISA SSVC: exploitation none, automatable no, technical impact total.
• Not listed in CISA KEV at the time of the sources.
• No public proof-of-concept found in the research; this is not confirmed absent.
• EPSS score 0.00353 (very low).

Our recommendation

• Apply the October 2026 cumulative update on all supported Windows systems without delay.
• Inventory all Windows 10 1607 / LTSB 2016 devices. According to Microsoft's release-health page, these devices no longer receive security updates as of 13 October 2026; plan an upgrade, replacement or Extended Security Updates (ESU). Confirm ESU availability with Microsoft.
• Restrict RDP to VPN or trusted networks and remove it from internet exposure.
• Limit local accounts and monitor for unusual privilege changes on RDP-enabled hosts.
• Verify build numbers directly in the MSRC table, as mirror sites differ on at least one value.

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-2026-83861 msrc.microsoft.com
• Microsoft release health: Windows 10 1607 and Windows Server 2016 learn.microsoft.com
• NVD mirror (Vulners): CVE-2026-83861 vulners.com
• VulDB: CVE-2026-83861 vuldb.com
• OpenCVE: CVE-2026-83861 app.opencve.io
• Zero Day Initiative: October 2026 Security Update Review www.zerodayinitiative.com
• Strix: CVE-2026-83861 www.strix.ai
• Windows 10 Enterprise LTSB 2016 end of support and ESU (4sysops) 4sysops.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, 02:46.