CVE-2026-42912 — Windows Telephony Service Elevation of Privilege Vulnerability

Executive Summary

Concurrent execution using shared resource with improper synchronization ('race condition') in Windows Telephony Service 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 0.00205 — 0.10722 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

0.00205

probability of exploitation in the next 30 days

0.10722 percentile - updated 2026-07-25

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 · tapisrv.dll (KB5094126)

Two race conditions fixed in the Windows Telephony Service RPC server. (1) Sub-mask index OOB: GetSubMaskIndex() return value was used without bounds validation to index into the per-object event mask array; patch adds a bounds check (index > 0x1e → error) via new GetEventMasksOrSubMasks helper, gated behind Feature_500158777. TGetEventMasksOrSubMasks was refactored from 1431 to 938 instructions by consolidating five per-object-type code-duplicated paths into a single call to this helper. (2) Conference participant UAF in DestroytCall: participant removed from conf slot array without holding exclusive access to the conf call object; patch acquires ReferenceObject + WaitForExclusivetCallAccess before modifying the conf participant list, gated behind Feature_784066872. Both fixes are feature-flagged (WIL DeviceUsage CFR) and inert until Microsoft enables the respective flags per cohort.

Pre-patch version 10.0.26100.8521 Download

Post-patch version 10.0.26100.8655 Download

Function	Address	Change	Note
`SetEventMasksOrSubMasks`	`18003787c -> 180037ad8`	code, length, address, called	similarity 0.51
`TGetEventMasksOrSubMasks`	`180037f10 -> 1800381a0`	code, length, address, called	similarity 0.31
`DestroytCall`	`180004c88`	code, length, sig, called	similarity 0.37

View full diff report View RCA report Download PoC

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

DongJun Kim

References

MSRC Advisory MITRE NVD