CVE-2026-32070 — Windows Common Log File System Driver Elevation of Privilege Vulnerability

Executive Summary

Use after free in Windows Common Log File System Driver allows an authorized attacker to elevate privileges locally.

Overview

7

CVSS HIGH

Important

MS Severity

Not Exploited

MS Exploit Status

More Likely

MS Exploit Likelihood

Category Elevation of Privilege

Weakness CWE-416: Use After Free

Released Apr 14 2026

Last Updated Apr 14 2026

Publicly Disclosed No

CISA KEV Not Listed

Known Exploits None Known

EPSS Score 0.0032 — 0.24633 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

0.0032

probability of exploitation in the next 30 days

0.24633 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 · clfs.sys (KB5083769)

Reference-count lifetime-inversion use-after-free (CWE-416) in the Windows CLFS driver clfs.sys CClfsManagedLog::AddNewClient. The function creates a COM-style reference-counted CClfsManagedLogClient, and pre-patch did: allocate + store in *a5, call Initialize (vtable+32) which registers the object EXTERNALLY (kernel structures / observer chains, e.g. InstallLogObserver), then finally AddRef (vtable+0). Because the object is published before any reference is held, its refcount is still 0 when other threads can find it; a concurrent Release drops the count below zero and frees the object, and the original thread's later AddRef touches freed memory -> UAF. The failure path also called the destructor directly (vtable+80, bFinal=1) rather than Release, which only balances the pre-patch ordering. Diff of clfs.sys 10.0.26100.8115 -> .8246 (Apr 14 2026, KB5083769) confirms AddNewClient is the changed function and gains a new CFR gate: gated behind Feature_1664551224, AddRef is moved BEFORE Initialize, and the failure path now calls Release (vtable+8) to balance the earlier AddRef; the list-insertion check became an explicit guard (if (*v18 != i) __fastfail(3u)) and control flow consolidated to a single LABEL_31 exit so the managed-log mutex is released once. All managed-log clients (CreateLogFile) reach this path. Note: our diff shows Feature_1664551224, differing from the circulated screenshots' Feature_1932986680 (build/arch difference); the AddRef-before-Initialize reorder is identical.

Pre-patch version 10.0.26100.8115 Download

Post-patch version 10.0.26100.8246 Download

Function	Address	Change	Note
`CClfsManagedLog::AddNewClient`	`code change`	code (AddRef reordered before Initialize; Release on failure; CFR-gated)	Pre: alloc -> Initialize(vtable+32, registers externally) -> AddRef(vtable+0); refcount 0 during external exposure -> concurrent Release frees object -> later AddRef is UAF; failure path called destructor directly (vtable+80,bFinal=1). Post (Feature_1664551224 enabled): AddRef(vtable+0) first, then Initialize; on failure Release(vtable+8) to balance; list-insert guard `if (*v18 != i) __fastfail(3u)`; single LABEL_31 exit (mutex released once).
`Feature_1664551224`	`gate`	added (CFR gate)	CFR flag gating the AddRef-first ordering + Release-on-failure fix; the original ordering still ships when disabled.

View full diff report View RCA report

Attack Path

AddNewClient registers a CLFS managed-log client externally before taking a reference, so a racing Release frees it under the creating thread

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.

Known Exploits

No known exploits have been linked for this CVE yet. When available, exploit references will be sourced from public repositories and may be unverified, incomplete, or non-functional. Always review code carefully before use in any environment.

Acknowledgments

Joe Desimone
Daniel Dutra
Henrique

References

MSRC Advisory MITRE NVD