CVE-2026-50378 — Windows Key Guard Elevation of Privilege Vulnerability

Executive Summary

Concurrent execution using shared resource with improper synchronization ('race condition') in Windows Key Guard 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-362: Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')

Released Jul 14 2026

Last Updated Jul 14 2026

Publicly Disclosed No

CISA KEV Not Listed

Known Exploits None Known

EPSS Score 0.00199 — 0.09994 percentile

NVD CVSS 7 HIGH — differs from 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: 6.8

EPSS Score

0.00199

probability of exploitation in the next 30 days

0.09994 percentile - updated 2026-08-14

View on FIRST.org

Affected Products

19 affected products

Product	KB Article	Severity	Impact	Restart Required
Windows 10 Version 1809 for 32-bit Systems	`5099538 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 1809 for x64-based Systems	`5099538 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 21H2 for 32-bit Systems	`5099539 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 21H2 for ARM64-based Systems	`5099539 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 21H2 for x64-based Systems	`5099539 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 22H2 for 32-bit Systems	`5099539 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 22H2 for ARM64-based Systems	`5099539 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 22H2 for x64-based Systems	`5099539 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 11 Version 24H2 for ARM64-based Systems	`5101650 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 11 Version 24H2 for x64-based Systems	`5101650 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 11 Version 25H2 for ARM64-based Systems	`5101650 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 11 Version 25H2 for x64-based Systems	`5101650 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 11 Version 26H1 for ARM64-based Systems	`5101649 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 11 version 26H1 for x64-based Systems	`5095051 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2019	`5099538 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2019 (Server Core installation)	`5099538 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2022	`5099540 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2025	`5099536 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2025 (Server Core installation)	`5099536 (Security Update)`	Important	Elevation of Privilege	Yes

Patches

7 patches

Article	Type	Restart
`5099538`	Security Update	Yes
`5099539`	Security Update	Yes
`5101650`	Security Update	Yes
`5101649`	Security Update	Yes
`5095051`	Security Update	Yes
`5099540`	Security Update	Yes
`5099536`	Security Update	Yes

Patch Diff

ghidriff · lsaiso.exe (KB5101650)

Race condition (CWE-362) in the Windows Key Guard isolated trustlet lsaiso.exe BCryptIum crypto-RPC objects, local EoP to SYSTEM. lsaiso.exe is the Isolated LSA / Key Guard trustlet (runs in VBS/IUM VTL1) and exposes a BCryptIum* RPC interface for isolated crypto operations; each key/context is a _BCRYPT_ISO_OBJECT tracked by the trustlet. PRE: access to a shared _BCRYPT_ISO_OBJECT across the BCryptIum operations was not synchronized, so concurrent RPC calls operating on the same object could race (use/modify it while another call used/freed it) - a race condition on the shared trustlet crypto object exploitable for local EoP to SYSTEM. Diff of lsaiso.exe 10.0.26100.8737 -> .8875 (Jul 14 2026, KB5101650) confirms the fix: the _BCRYPT_ISO_OBJECT gains a per-object SRW lock (a lock field at object+0x28); AllocateBCryptIsoObject initializes it and the BCryptIum operations (Encrypt/Decrypt/DeriveKey/CreateClaim/DuplicateKey/DestroyKey/... via LookupBCryptIsoObject) now AcquireSRWLockExclusive/ReleaseSRWLockExclusive around access to the shared object, serializing concurrent operations and closing the race. Note: this July update reworks the whole BCryptIum trustlet interface; the CWE-362 race fix is the per-object SRW-lock serialization isolated here. The paired Key Guard CVE-2026-50303 (CWE-1240, risky crypto primitive) is in the same binary but its distinct crypto change was not cleanly isolable in this diff and is not claimed here.

Pre-patch version 10.0.26100.8737 Download

Post-patch version 10.0.26100.8875 Download

Function	Address	Change	Note
`AllocateBCryptIsoObject`	`code change`	code (per-object SRW lock added)	The allocated _BCRYPT_ISO_OBJECT now carries an SRW lock (field at +0x28) initialized here; AcquireSRWLockExclusive/ReleaseSRWLockExclusive imported and used.
`BCryptIum* operations (Encrypt/Decrypt/DeriveKey/SecretAgreement/CreateClaim/DuplicateKey/DestroyKey/ImportKey/ExportKey/...)`	`code change`	code (serialized access to the shared ISO object)	These RPC handlers now look up the _BCRYPT_ISO_OBJECT and take the per-object SRW lock around access, serializing concurrent operations on the same trustlet crypto object.
`race-fix`	`n/a`	note	Direct fix (not CFR-gated). ~36 BCryptIum functions changed as part of the interface rework; the CWE-362 fix is the added per-object SRW-lock serialization.

View full diff report View RCA report

Attack Path

Concurrent BCryptIum RPC calls race on a shared Key Guard trustlet crypto object with no lock

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

Leshi Yang

References

MSRC Advisory MITRE NVD