Windows AppX Deployment Service: Local privilege escalation via link following

Summary

The Windows AppX Deployment Service (AppXSVC) on Windows 10, Windows 11 and Windows Server contains an improper link resolution flaw (CWE-59) before file access. An authorized local user with low privileges can exploit it to gain higher privileges, with high impact on confidentiality, integrity and availability. Remote exploitation is not indicated; the attacker needs local access to the affected system.

Affected

• Windows 10 Version 1607 and Windows Server 2016 (including Server Core): builds 10.0.14393.0 to below 10.0.14393.9612
• Windows 10 Version 1809 and Windows Server 2019 (including Server Core): builds 10.0.17763.0 to below 10.0.17763.9376
• Windows 10 Version 21H2: builds 10.0.19044.0 to below 10.0.19044.7807
• Windows 10 Version 22H2: builds 10.0.19045.0 to below 10.0.19045.7807
• Windows 11 Version 23H2: builds 10.0.22631.0 to below 10.0.22631.7652
• Windows 11 Version 24H2: builds 10.0.26100.0 to below 10.0.26100.9711
• Windows 11 Version 25H2: builds 10.0.26200.0 to below 10.0.26200.9711
• Windows 11 Version 26H1: builds 10.0.28000.0 to below 10.0.28000.3231
• Windows 11 Version 26H2: builds 10.0.26300.0 to below 10.0.26300.9711
• Windows Server 2022: builds 10.0.20348.0 to below 10.0.20348.5761

Fixed in

• Fixed builds per CVE record (first build not affected): 10.0.14393.9612 (1607 and Server 2016), 10.0.17763.9376 (1809 and Server 2019), 10.0.19044.7807 (21H2), 10.0.19045.7807 (22H2), 10.0.22631.7652 (23H2), 10.0.26100.9711 (24H2), 10.0.26200.9711 (25H2), 10.0.28000.3231 (26H1), 10.0.26300.9711 (26H2), 10.0.20348.5761 (Server 2022)
• Fixes are delivered with the October 2026 security update. Verify the exact build on the MSRC advisory.

Workaround

Unknown. No Microsoft workaround could be verified.

• Restrict local logon to trusted users.
• Limit valid local accounts on affected hosts.

Exploitation

• CISA SSVC: exploitation none, not automatable, technical impact total.
• No public proof of concept and no confirmed in-the-wild exploitation was found at the time of writing.

Our recommendation

• Inventory all Windows 10 1607 and Windows Server 2016 hosts, including OT and fixed-function devices.
• Install the October 2026 security update on all affected systems and verify the build number.
• Plan migration off Windows 10 Enterprise 2016 LTSB now. Research notes indicate that support ends on 13 October 2026, so further fixes may not be provided.
• Review local accounts and administrator rights on these hosts.

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

• MSRC Security Update Guide: CVE-2026-85849 msrc.microsoft.com
• NVD mirror (Vulners): CVE-2026-85849 vulners.com
• OpenCVE: CVE-2026-85849 app.opencve.io
• Vulners MSCVE tracker: MS:CVE-2026-85849 vulners.com
• Microsoft Windows release information learn.microsoft.com
• Qualys: Microsoft Patch Tuesday October 2026 review blog.qualys.com
• VulDB: CVE-2026-85849 vuldb.com
• Insentra: Windows 10 LTSB is ending www.insentragroup.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, 01:57.