CVE-2026-42968 — Windows Telephony Server Information Disclosure Vulnerability

Executive Summary

Out-of-bounds read in Windows Telephony Service allows an authorized attacker to disclose information locally.

Overview

5.5

CVSS MEDIUM

Important

MS Severity

Not Exploited

MS Exploit Status

Less Likely

MS Exploit Likelihood

Category Information Disclosure

Weakness CWE-125: Out-of-bounds Read

Released Jun 9 2026

Last Updated Jun 9 2026

Publicly Disclosed No

CISA KEV Not Listed

Known Exploits None Known

EPSS Score 0.00388 — 0.31838 percentile

NVD CVSS 5.5 MEDIUM — matches MSRC

CVSS Vector

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

ATTACK VECTOR

Local

ATTACK COMPLEXITY

Low

PRIVILEGES REQUIRED

Low

USER INTERACTION

None

SCOPE

Unchanged

CONFIDENTIALITY

High

INTEGRITY

None

AVAILABILITY

None

EXPLOIT CODE MATURITY

Unproven

REMEDIATION LEVEL

Official Fix

REPORT CONFIDENCE

Confirmed

Temporal Score: 4.8

EPSS Score

0.00388

probability of exploitation in the next 30 days

0.31838 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	Information Disclosure	Yes
Windows 10 Version 1607 for x64-based Systems	`5094122 (Security Update)`	Important	Information Disclosure	Yes
Windows 10 Version 1809 for 32-bit Systems	`5094123 (Security Update)`	Important	Information Disclosure	Yes
Windows 10 Version 1809 for x64-based Systems	`5094123 (Security Update)`	Important	Information Disclosure	Yes
Windows 10 Version 21H2 for 32-bit Systems	`5094127 (Security Update)`	Important	Information Disclosure	Yes
Windows 10 Version 21H2 for ARM64-based Systems	`5094127 (Security Update)`	Important	Information Disclosure	Yes
Windows 10 Version 21H2 for x64-based Systems	`5094127 (Security Update)`	Important	Information Disclosure	Yes
Windows 10 Version 22H2 for 32-bit Systems	`5094127 (Security Update)`	Important	Information Disclosure	Yes
Windows 10 Version 22H2 for ARM64-based Systems	`5094127 (Security Update)`	Important	Information Disclosure	Yes
Windows 10 Version 22H2 for x64-based Systems	`5094127 (Security Update)`	Important	Information Disclosure	Yes
Windows 11 Version 23H2 for ARM64-based Systems	`5093998 (Security Update)`	Important	Information Disclosure	Yes
Windows 11 Version 23H2 for x64-based Systems	`5093998 (Security Update)`	Important	Information Disclosure	Yes
Windows 11 Version 24H2 for ARM64-based Systems	`5094126 (Security Update)`	Important	Information Disclosure	Yes
Windows 11 Version 24H2 for x64-based Systems	`5094126 (Security Update)`	Important	Information Disclosure	Yes
Windows 11 Version 25H2 for ARM64-based Systems	`5094126 (Security Update)`	Important	Information Disclosure	Yes
Windows 11 Version 25H2 for x64-based Systems	`5094126 (Security Update)`	Important	Information Disclosure	Yes
Windows 11 Version 26H1 for ARM64-based Systems	`5095051 (Security Update)`	Important	Information Disclosure	Yes
Windows 11 version 26H1 for x64-based Systems	`5095051 (Security Update)`	Important	Information Disclosure	Yes
Windows Server 2012	`5094042 (Monthly Rollup)`	Important	Information Disclosure	Yes
Windows Server 2012 (Server Core installation)	`5094042 (Monthly Rollup)`	Important	Information Disclosure	Yes
Windows Server 2012 R2	`5094041 (Monthly Rollup)`	Important	Information Disclosure	Yes
Windows Server 2012 R2 (Server Core installation)	`5094041 (Monthly Rollup)`	Important	Information Disclosure	Yes
Windows Server 2016	`5094122 (Security Update)`	Important	Information Disclosure	Yes
Windows Server 2016 (Server Core installation)	`5094122 (Security Update)`	Important	Information Disclosure	Yes
Windows Server 2019	`5094123 (Security Update)`	Important	Information Disclosure	Yes
Windows Server 2019 (Server Core installation)	`5094123 (Security Update)`	Important	Information Disclosure	Yes
Windows Server 2022	`5094128 (Security Update)`	Important	Information Disclosure	Yes
Windows Server 2022 (Server Core installation)	`5094128 (Security Update)`	Important	Information Disclosure	Yes
Windows Server 2025	`5094125 (Security Update)`	Important	Information Disclosure	Yes
Windows Server 2025 (Server Core installation)	`5094125 (Security Update)`	Important	Information Disclosure	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)

Out-of-bounds read (CWE-125) in the Windows Telephony Server tapisrv.dll TAPI event-mask handling, local information disclosure over the Telephony RPC interface. TAPI stores per-object event state as a 31-entry DWORD array (valid index 0-30). In single sub-mask mode (request+0x10 != 0) the handler combines request+0x18/+0x1C into a 64-bit sub-mask and derives an array index via GetSubMaskIndex = floor(log2(submask)), which can be up to 63. PRE: neither the read helper nor the write helper checked idx against the 31-slot array, so a sub-mask with bit 63 set yields idx=63 and reads base[63] - 132 bytes past the last valid entry base[30]. On the read path (TGetEventMasksOrSubMasks, 6 per-object accesses) the OOB DWORD is written to request+0x14 and returned in the RPC response (4-byte disclosure of adjacent TAPI memory); the same unbounded index reaches an OOB array write on SetEventMasksOrSubMasks. IN-HOUSE ghidriff of tapisrv.dll 10.0.26100.8521 -> .8655 (Jun 9 2026, KB5094126) confirms the fix: a new GetEventMasksOrSubMasks read helper and SetEventMasksOrSubMasks add an index bound (0x1e < idx -> return 0x80000032) at 7 access points, gated behind CFR flag Feature_500158777 (TGet also references Feature_784066872). Note: our x64 24H2 diff shows Feature_500158777/784066872, differing from the circulated screenshots' Feature_768594233 (build/arch difference); the >= 0x1F bound and 0x80000032 error are identical. We ship what our diff shows.

Pre-patch version 10.0.26100.8521 Download

Post-patch version 10.0.26100.8655 Download

Function	Address	Change	Note
`GetEventMasksOrSubMasks`	`new helper`	added (bounded read helper, CFR-gated)	New per-object read helper used by TGetEventMasksOrSubMasks. Single sub-mask branch: idx=GetSubMaskIndex(submask); if Feature_500158777 enabled and 0x1e<idx (>=31) return 0x80000032 else *param_4=param_5[idx]. Bound absent pre-patch (base[idx] read up to base[63]).
`SetEventMasksOrSubMasks`	`code change`	code (index bound added, CFR-gated)	Common write helper for the 6 per-object setters. Pre: param_4[GetSubMaskIndex(submask)] = value with no bound. Post: if Feature_500158777 enabled and 0x1e<idx return 0x80000032 before the write. Whole-mask loop (lVar=0x1f, 31 iterations) unchanged.
`TGetEventMasksOrSubMasks`	`code change`	code (read path refactored to bounded helper)	Read path; 6 per-object accesses refactored through GetEventMasksOrSubMasks; references Feature_784066872 in addition to Feature_500158777. The OOB DWORD was returned via request+0x14 in the RPC response pre-patch.
`Feature_500158777`	`new flag`	added (CFR gate)	New CFR flag gating the idx>=0x1F bound on the shared read/write helpers.
`Feature_784066872`	`new flag`	added (CFR gate)	Second new CFR flag referenced on the TGetEventMasksOrSubMasks read path.

View full diff report View RCA report

Attack Path

A 64-bit TAPI sub-mask yields an array index up to 63 that reads past the 31-entry event-mask array and leaks the DWORD via RPC

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

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References

MSRC Advisory MITRE NVD