CVE-2026-83999

highpriority · track · 28EPSS 0.003 · 21 %ileDERUUS

grimoire priorityP2 · Scheduled

Exploitable?

—

no known exploitation

Likely / severe?

0.28% (21st) EPSS

CVSS 7 · high

Is it mine?

33 products

Check your exposure

Who says so?

3 sources

fstec_bdu · cert_bund · msrc_csaf

EPSS · scored 2026-10-27

Improper link resolution before file access ('link following') in Windows Resilient File System (ReFS) Deduplication Service allows an authorized attacker to elevate privileges locally.

remediations

Vendor fix, mitigation, or workaround guidance, as published by each source.

A vendor fix is available.

FixedWindows 11 Version 24H2 for ARM64-based Systemsmsrc_csaf
10.0.26100.9445:Security Update:https://support.microsoft.com/help/5124008
https://support.microsoft.com/help/5124008
FixedWindows 11 Version 24H2 for x64-based Systemsmsrc_csaf
10.0.26100.9445:Security Update:https://support.microsoft.com/help/5124008
https://support.microsoft.com/help/5124008
FixedWindows 11 Version 25H2 for ARM64-based Systemsmsrc_csaf
10.0.26200.9445:Security Update:https://support.microsoft.com/help/5124008
https://support.microsoft.com/help/5124008
FixedWindows 11 Version 25H2 for x64-based Systemsmsrc_csaf
10.0.26200.9445:Security Update:https://support.microsoft.com/help/5124008
https://support.microsoft.com/help/5124008
FixedWindows 11 Version 26H1 for ARM64-based Systemsmsrc_csaf
10.0.28000.2954:Security Update:https://support.microsoft.com/help/5124012
https://support.microsoft.com/help/5124012
FixedWindows 11 version 26H1 for x64-based Systemsmsrc_csaf
10.0.28000.2954:Security Update:https://support.microsoft.com/help/5124012
https://support.microsoft.com/help/5124012
FixedWindows Server 2025msrc_csaf
10.0.26100.33438:Security Update:https://support.microsoft.com/help/5122871
https://support.microsoft.com/help/5122871
FixedWindows Server 2025 (Server Core installation)msrc_csaf
10.0.26100.33438:Security Update:https://support.microsoft.com/help/5122871
https://support.microsoft.com/help/5122871

cvss

Technical severity, 0–10. One row per scoring source.

7.0

010

base score 0–10 · higher = more severe · hover a vector to decode⚠ sources disagree · medium–high · 6.4–7

v3.17highCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:Hprimary · secure@microsoft.com USexploitability 1 · impact 5.9

v3.17highAV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:Hsecondary · FSTEC (BDU) RU

v3.16.4mediumCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H/E:Usecondary · CVSS-BT (t0sche)

v3.17highCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:Csecondary · Microsoft Security Response Center US

ssvc

A stakeholder decision — act, attend, or track — from exploitation and impact.

Exploitation: none · Automatable: no · Technical Impact: totalcoordinatorcisa_ssvcUS

weaknesses

The CWE weakness classes this flaw belongs to.

CWE-59USCWE-59USCWE-59US

affected products (33)

Products and version ranges known to be affected.

Microsoft Windows 10all versionscert_bundDEcpe:/o:microsoft:windows_10:-
Microsoft Windows 11all versionscert_bundDEcpe:/o:microsoft:windows_11:-
Microsoft Windows Server 2012all versionscert_bundDEcpe:/o:microsoft:windows_server_2012:-
Microsoft Windows Server 2012 R2all versionscert_bundDEcpe:/o:microsoft:windows_server_2012_r2:-
Microsoft Windows Server 2016all versionscert_bundDEcpe:/o:microsoft:windows_server_2016:-
Microsoft Windows Server 2019all versionscert_bundDEcpe:/o:microsoft:windows_server_2019:-
Microsoft Windows Server 2022all versionscert_bundDEcpe:/o:microsoft:windows_server_2022:-
Microsoft Windows Server 2025all versionscert_bundDEcpe:/o:microsoft:windows_server_2025:-
Microsoft Corp Windows 11 24H2≤ 10.0.26100.9445fstec_bduRU
Microsoft Corp Windows 11 25H2≤ 10.0.26200.9445fstec_bduRU
Microsoft Corp Windows 11 26H1≤ 10.0.28000.2954fstec_bduRU
Microsoft Corp Windows Server 2025≤ 10.0.26100.33438fstec_bduRU
Microsoft Corp Windows Server 2025 (Server Core installation)≤ 10.0.26100.33438fstec_bduRU
Microsoft Windows 11 Version 24H2 for ARM64-based Systemsall versionsfixedmsrc_csafUS
Microsoft Windows 11 Version 24H2 for ARM64-based Systems< 10.0.26100.9445msrc_csafUS
Microsoft Windows 11 Version 24H2 for x64-based Systemsall versionsfixedmsrc_csafUS
Microsoft Windows 11 Version 24H2 for x64-based Systems< 10.0.26100.9445msrc_csafUS
Microsoft Windows 11 Version 25H2 for ARM64-based Systemsall versionsfixedmsrc_csafUS
Microsoft Windows 11 Version 25H2 for ARM64-based Systems< 10.0.26200.9445msrc_csafUS
Microsoft Windows 11 Version 25H2 for x64-based Systemsall versionsfixedmsrc_csafUS

showing 20 of 33

advisories (2)

Vendor and ecosystem advisories describing this.

WID-SEC-W-2026-3243Microsoft Windows: Mehrere SchwachstellenDeutsch2026-09-08csaf · cert_bundDE
Ein Angreifer kann mehrere Schwachstellen in verschiedenen Versionen von Microsoft Windows Server, Microsoft Windows 10 und Microsoft Windows 11 ausnutzen, um seine Privilegien zu erhöhen, um einen Denial of Service herbeizuführen, um Informationen offenzulegen und um beliebigen Code auszuführen.
msrc_CVE-2026-83999Windows Resilient File System (ReFS) Deduplication Service Elevation of Privilege Vulnerability2026-09-08csaf · msrc_csafUS
To determine the support lifecycle for your software, see the Microsoft Support Lifecycle: https://support.microsoft.com/lifecycle

also known as (1)

Other names and identifiers for this entity.

BDU:2026-14843 fstec_bdu

sources

Which sources assert this record, and when.

fstec_bdu cert_bund msrc_csaf NVD CVE.org MITRE

published 2026-09-08modified 2026-09-18

references (1) nvd

External citations — patches, advisories, analysis.

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-83999PatchVendor Advisory

scry

Attackers weaponise vulnerabilities like this against internet-exposed services. See what is exposed on your perimeter with a free passive scan.

Free scan