CVE-2026-42836 — Windows Function Discovery Service (fdwsd.dll) Elevation of Privilege Vulnerability

Executive Summary

Concurrent execution using shared resource with improper synchronization ('race condition') in Function Discovery Service (fdwsd.dll) 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 Jun 9 2026

Last Updated Jun 9 2026

Publicly Disclosed No

CISA KEV Not Listed

Known Exploits None Known

EPSS Score 0.00198 — 0.0982 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

0.00198

probability of exploitation in the next 30 days

0.0982 percentile - updated 2026-08-14

View on FIRST.org

Affected Products

30 affected products

Product	KB Article	Severity	Impact	Restart Required
Windows 10 Version 1607 for 32-bit Systems	`5094122 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 1607 for x64-based Systems	`5094122 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 1809 for 32-bit Systems	`5094123 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 1809 for x64-based Systems	`5094123 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 21H2 for 32-bit Systems	`5094127 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 21H2 for ARM64-based Systems	`5094127 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 21H2 for x64-based Systems	`5094127 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 22H2 for 32-bit Systems	`5094127 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 22H2 for ARM64-based Systems	`5094127 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 10 Version 22H2 for x64-based Systems	`5094127 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 11 Version 23H2 for ARM64-based Systems	`5093998 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 11 Version 23H2 for x64-based Systems	`5093998 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 11 Version 24H2 for ARM64-based Systems	`5094126 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 11 Version 24H2 for x64-based Systems	`5094126 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 11 Version 25H2 for ARM64-based Systems	`5094126 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 11 Version 25H2 for x64-based Systems	`5094126 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 11 Version 26H1 for ARM64-based Systems	`5095051 (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 2012	`5094042 (Monthly Rollup)`	Important	Elevation of Privilege	Yes
Windows Server 2012 (Server Core installation)	`5094042 (Monthly Rollup)`	Important	Elevation of Privilege	Yes
Windows Server 2012 R2	`5094041 (Monthly Rollup)`	Important	Elevation of Privilege	Yes
Windows Server 2012 R2 (Server Core installation)	`5094041 (Monthly Rollup)`	Important	Elevation of Privilege	Yes
Windows Server 2016	`5094122 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2016 (Server Core installation)	`5094122 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2019	`5094123 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2019 (Server Core installation)	`5094123 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2022	`5094128 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2022 (Server Core installation)	`5094128 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2025	`5094125 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2025 (Server Core installation)	`5094125 (Security Update)`	Important	Elevation of Privilege	Yes

Patches

10 patches

Article	Type	Restart
`5094122`	Security Update	Yes
`5094123`	Security Update	Yes
`5094127`	Security Update	Yes
`5093998`	Security Update	Yes
`5094126`	Security Update	Yes
`5095051`	Security Update	Yes
`5094042`	Monthly Rollup	Yes
`5094041`	Monthly Rollup	Yes
`5094128`	Security Update	Yes
`5094125`	Security Update	Yes

Patch Diff

ghidriff · fdwsd.dll (KB5094126)

Race condition (CWE-362) leading to use-after-free (CWE-416) in the Windows Function Discovery WSD provider fdwsd.dll CWSDiscoveryProvider, local EoP to SYSTEM (AC:H race). fdwsd.dll implements the WS-Discovery provider for the Function Discovery service; a CWSDiscoveryProvider object holds shared state (including a client certificate context and discovery members) that WSD discovery callbacks (IsInterestedInDevice / IsInterestedInMex) access on discovery events. PRE: access to that shared provider state was not synchronized, so a discovery callback could use the provider's state (or its certificate context) concurrently with another thread modifying it or with the provider being destroyed - a race that yields a use-after-free of the provider state / certificate. Because the service runs as SYSTEM/LocalService and the provider is driven by network-triggered discovery events, winning the race is a local EoP primitive. Diff of fdwsd.dll 10.0.26100.8521 -> .8655 (Jun 9 2026, KB5094126) confirms the fix: CWSDiscoveryProvider gains a CRITICAL_SECTION member (at object+0x128); the destructor now nulls the shared member (+0x98) under the lock, IsInterestedInDevice/IsInterestedInMex take the critical section around access to the shared state, and GetClientCertificate returns a private duplicate via CertDuplicateCertificateContext under the lock instead of handing out the shared certificate pointer - serializing access and giving callers their own reference so the shared object cannot be freed while in use.

Pre-patch version 10.0.26100.8521 Download

Post-patch version 10.0.26100.8655 Download

Function	Address	Change	Note
`CWSDiscoveryProvider::~CWSDiscoveryProvider`	`code change`	code (teardown under critical section)	Post: EnterCriticalSection(this+0x128); nulls the shared member (this+0x98)=0; LeaveCriticalSection - so teardown can't race a concurrent callback.
`CWSDiscoveryProvider::IsInterestedInDevice / IsInterestedInMex`	`code change`	code (callback access serialized)	Post: take the critical section (this+0x128) around access to the shared provider state during discovery-event evaluation.
`CWSDiscoveryProvider::GetClientCertificate`	`code change`	code (returns a duplicated cert under lock)	Post: under the critical section, returns CertDuplicateCertificateContext(...) so callers get their own reference instead of the shared certificate context.
`CRITICAL_SECTION @ +0x128`	`struct change`	added	New per-provider lock serializing destructor and discovery-callback access to shared state.

View full diff report View RCA report

Attack Path

WSD discovery callbacks use a CWSDiscoveryProvider's shared state concurrently with its teardown, causing a UAF

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

AIフィジカルインターフェイス二号機

References

MSRC Advisory MITRE NVD