CVE-2026-27929 — Windows LUA File Virtualization Filter Driver Elevation of Privilege Vulnerability

Executive Summary

Time-of-check time-of-use (toctou) race condition in Windows LUAFV allows an authorized attacker to elevate privileges locally.

Overview

7

CVSS HIGH

Important

MS Severity

Not Exploited

MS Exploit Status

Less Likely

MS Exploit Likelihood

Category Elevation of Privilege

Weakness CWE-367: Time-of-check Time-of-use (TOCTOU) Race Condition

Released Apr 14 2026

Last Updated Apr 14 2026

Publicly Disclosed No

CISA KEV Not Listed

Known Exploits None Known

EPSS Score 0.00186 — 0.08483 percentile

NVD CVSS 7 HIGH — matches MSRC

CVSS Vector

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C

ATTACK VECTOR

Local

ATTACK COMPLEXITY

High

PRIVILEGES REQUIRED

Low

USER INTERACTION

None

SCOPE

Unchanged

CONFIDENTIALITY

High

INTEGRITY

High

AVAILABILITY

High

EXPLOIT CODE MATURITY

Unproven

REMEDIATION LEVEL

Official Fix

REPORT CONFIDENCE

Confirmed

Temporal Score: 6.1

EPSS Score

0.00186

probability of exploitation in the next 30 days

0.08483 percentile - updated 2026-08-14

View on FIRST.org

Affected Products

31 affected products

Product	KB Article	Severity	Impact	Restart Required
Windows 10 Version 1607 for 32-bit Systems	`5082198 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 1607 for x64-based Systems	`5082198 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 1809 for 32-bit Systems	`5082123 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 1809 for x64-based Systems	`5082123 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 21H2 for 32-bit Systems	`5082200 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 21H2 for ARM64-based Systems	`5082200 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 21H2 for x64-based Systems	`5082200 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 22H2 for 32-bit Systems	`5082200 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 22H2 for ARM64-based Systems	`5082200 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 22H2 for x64-based Systems	`5082200 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 11 Version 23H2 for ARM64-based Systems	`5082052 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 11 Version 23H2 for x64-based Systems	`5082052 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 11 Version 24H2 for ARM64-based Systems	`5083769 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 11 Version 24H2 for x64-based Systems	`5083769 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 11 Version 25H2 for ARM64-based Systems	`5083769 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 11 Version 25H2 for x64-based Systems	`5083769 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 11 Version 26H1 for ARM64-based Systems	`5083768 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 11 version 26H1 for x64-based Systems	`5083768 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2012	`5082127 (Monthly Rollup)`	Important	Elevation of Privilege	Yes
Windows Server 2012 (Server Core installation)	`5082127 (Monthly Rollup)`	Important	Elevation of Privilege	Yes
Windows Server 2012 R2	`5082126 (Monthly Rollup)`	Important	Elevation of Privilege	Yes
Windows Server 2012 R2 (Server Core installation)	`5082126 (Monthly Rollup)`	Important	Elevation of Privilege	Yes
Windows Server 2016	`5082198 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2016 (Server Core installation)	`5082198 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2019	`5082123 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2019 (Server Core installation)	`5082123 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2022	`5082142 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2022 (Server Core installation)	`5082142 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2022, 23H2 Edition (Server Core installation)	`5082060 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2025	`5082063 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2025 (Server Core installation)	`5082063 (Security Update)`	Important	Elevation of Privilege	Yes

Patches

11 patches

Article	Type	Restart
`5082198`	Security Update	Yes
`5082123`	Security Update	Yes
`5082200`	Security Update	Yes
`5082052`	Security Update	Yes
`5083769`	Security Update	Yes
`5083768`	Security Update	Yes
`5082127`	Monthly Rollup	Yes
`5082126`	Monthly Rollup	Yes
`5082142`	Security Update	Yes
`5082060`	Security Update	Yes
`5082063`	Security Update	Yes

Patch Diff

ghidriff · luafv.sys (KB5083769)

Time-of-check/time-of-use race (CWE-367) in the Windows LUA File Virtualization filter driver luafv.sys store-directory query, local EoP to SYSTEM (AC:H race). LUAFV virtualizes file access for legacy apps into a per-user virtualization store; LuafvQueryStoreDirectory resolves/opens the store directory (via LuafvOpenDirectory) and uses it. PRE: the store-directory resolution had a time-of-check/time-of-use window - the directory checked and the directory subsequently opened/used were not bound to the same object, so a local user could swap the path/target between check and use to redirect the privileged store operation. Diff of luafv.sys 10.0.26100.7920 -> .8246 (Apr 14 2026, KB5083769) confirms the fix: gated behind CFR flag Feature_3287483706, LuafvQueryStoreDirectory is restructured so the store-directory object is captured once (cached at the context, param_3+0x20 / +0x60) and the LuafvOpenDirectory calls reissue consistently against that captured object, binding the check and use to the same directory and closing the TOCTOU window. Note: LuafvQueryStoreDirectory is the sole changed function and is confirmed code-changed under Feature_3287483706; the exact check/use instruction pairing is not fully isolable in the restructure, so the mechanism is stated at confirmed-changed level per the CWE-367 classification.

Pre-patch version 10.0.26100.7920 Download

Post-patch version 10.0.26100.8246 Download

Function	Address	Change	Note
`LuafvQueryStoreDirectory`	`code change`	code (store-directory resolution TOCTOU-hardened, CFR-gated)	Post (Feature_3287483706): captures the store-directory object once (cached at param_3+0x20 / +0x60) and reissues LuafvOpenDirectory consistently against it, so the checked directory and the used directory are the same object (closes the TOCTOU).
`Feature_3287483706`	`gate`	added (CFR gate)	CFR flag gating the TOCTOU-hardened store-directory resolution; the original path still ships when disabled.

View full diff report View RCA report

Attack Path

The LUAFV virtualization store directory is checked and then reopened, allowing a swap between check and use

Derived from the patch delta: the checks added by the vendor identify which fields crossed a trust boundary unvalidated. Reachability and privilege are taken from the call chain in the RCA report.

Exploits & PoC

No public exploit or PoC has been linked for this CVE yet. When available, references are sourced from public repositories and may be unverified or non-functional — review carefully before use.

Detection Rules

No public Sigma or Nuclei detection rule has been mapped to this CVE yet. Coverage is concentrated on exploited / high-profile vulnerabilities; check SigmaHQ for updates.

Acknowledgments

Souhail Hammou

References

MSRC Advisory MITRE NVD