Windows exFAT File System: Heap overflow enables local privilege escalation

Summary

A heap-based buffer overflow in the Windows exFAT File System driver allows local privilege escalation. An attacker who already has a low-privilege account on the affected Windows system can gain higher privileges. Microsoft rates the CVE 7.8 (High), but reports no public disclosure and no exploitation, and assesses exploitation as unlikely.

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

• Install the Microsoft October 2026 security update for each affected build.
• Windows 10 Version 1607 / Server 2016: 10.0.14393.9612 or later
• Windows 10 Version 1809: 10.0.17763.9376 or later
• Windows 10 Version 21H2: 10.0.19044.7807 or later
• Windows 10 Version 22H2: 10.0.19045.7807 or later
• Windows 11 Version 23H2: 10.0.22631.7652 or later
• Windows 11 Version 24H2 and 25H2 and 26H2: 10.0.26100.9711 / 10.0.26200.9711 / 10.0.26300.9711 or later
• Windows 11 Version 26H1: 10.0.28000.3231 or later
• Windows Server 2012 and 2012 R2: 6.2.9200.26434 / 6.3.9600.23470 or later

Workaround

• No Microsoft-documented workaround known.
• Interim measure (own recommendation): restrict local logons on shared machines and limit use of untrusted USB sticks and SD cards until the update is installed.
• Disabling exFAT support is not a routine change and was not verified as a safe mitigation; test before use.

Exploitation

• Publicly disclosed: No.
• Exploited in the wild: No.
• Microsoft exploitability assessment: Exploitation Unlikely.
• EPSS about 0.4 % (below 1 %).
• No public proof of concept found in the research; this is not proof that none exists.

Our recommendation

• Patch first: Windows 10 Version 1607 and Server 2016, then all other affected builds in the normal update cycle.
• Check whether Windows 10 Version 1607 is still supported for your edition; if it is out of support, plan a replacement.
• Verify the installed build after patching (winver or systeminfo).
• Identify shared PCs, terminal servers and RDS hosts, and prioritise them.
• Check that CVE-2026-85822 (a separate exFAT elevation of privilege CVE) is covered by the same update.

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-2026-83881 msrc.microsoft.com
• CVE-2026-83881 CNA record (vulners CVELIST) vulners.com
• NVD: CVE-2026-83881 (vulners mirror) vulners.com
• OpenCVE: CVE-2026-83881 app.opencve.io
• Microsoft Security Update Guide: CVE-2026-85822 (related exFAT CVE) msrc.microsoft.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, 02:42.