Microsoft Remote Desktop Client: Remote code execution via heap-based buffer overflow

Summary

A heap-based buffer overflow in the Windows Remote Desktop Client allows an unauthorized attacker to execute code over the network. The CVSS vector (AV:N/AC:H/PR:N/UI:R) indicates high attack complexity and required user interaction, so exploitation is harder than for a wormable flaw. Microsoft has released fixes for the affected Windows 10, Windows 11 and Windows Server builds.

Affected

• Windows 10 Version 1607 and Windows Server 2016 (including Server Core): 10.0.14393.0 to before 10.0.14393.9688
• Windows 10 Version 1809 and Windows Server 2019 (including Server Core): 10.0.17763.0 to before 10.0.17763.9487
• Windows 10 Version 21H2: 10.0.19044.0 to before 10.0.19044.7846
• Windows 10 Version 22H2: 10.0.19045.0 to before 10.0.19045.7846
• Windows 11 Version 23H2: 10.0.22631.0 to before 10.0.22631.7711
• Windows 11 Version 24H2: 10.0.26100.0 to before 10.0.26100.9974
• Windows 11 Version 25H2: 10.0.26200.0 to before 10.0.26200.9974
• Windows 11 Version 26H1: 10.0.28000.0 to before 10.0.28000.3501
• Windows 11 Version 26H2: 10.0.26300.0 to before 10.0.26300.9974
• Windows Server 2022: 10.0.20348.0 to before 10.0.20348.5870

Fixed in

• Fixed in the November 2026 cumulative updates for the affected builds listed above (build numbers as stated in the CVE record; confirm the KB numbers on the MSRC advisory).

Workaround

Unknown.

Exploitation

• Not known to be exploited in the wild for this CVE. Rapid7 and Tenable identify a different November 2026 zero-day (CVE-2026-124194).
• No public proof of concept found.
• Microsoft's exploitability assessment: unknown.
• CISA SSVC: exploitation none, automatable no, technical impact total.

Our recommendation

• Install the November 2026 cumulative update on all affected Windows workstations and servers in the regular patch cycle.
• Check the MSRC advisory for the exact KB numbers and any later exploitation flag.
• Restrict RDP access to trusted networks and keep Network Level Authentication enabled.
• Warn staff not to connect to unfamiliar RDP hosts and to be cautious with RDP files from untrusted sources.
• Monitor for unusual RDP sessions and raise priority if exploitation is reported.

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-2026-119858 msrc.microsoft.com
• CVE Record CVE-2026-119858 (CVE.org) www.cve.org
• Strix: CVE-2026-119858 www.strix.ai
• Rapid7: Patch Tuesday November 2026 www.rapid7.com
• Tenable: Microsoft Patch Tuesday November 2026 www.tenable.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, 05:31.