OnlyPatch
Windows Telephony Service

CVE-2024-43626 — Windows Telephony Service Elevation of Privilege Vulnerability

Important CVSS 7.8 EPSS 0.00726 🔬 Patch diffed 2024-11 archive

Executive Summary

None

Overview

7.8
CVSS HIGH
Important
MS Severity
Not Exploited
MS Exploit Status
Less Likely
MS Exploit Likelihood
Category Elevation of Privilege
Weakness CWE-122: Heap-based Buffer Overflow
Released Nov 12 2024
Last Updated Nov 12 2024
Publicly Disclosed No
CISA KEV Not Listed
Known Exploits None Known
EPSS Score 0.00726 — 0.50963 percentile
NVD CVSS 7.8 HIGH — matches MSRC

CVSS Vector

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

0.00726
probability of exploitation in the next 30 days
0.50963 percentile - updated 2026-08-14
View on FIRST.org

Affected Products

25 affected products
Product KB Article Severity Impact Restart Required
Windows 10 for 32-bit Systems 5046665 (Security Update) Important Elevation of Privilege Yes
Windows 10 for x64-based Systems 5046665 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 1607 for 32-bit Systems 5046612 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 1607 for x64-based Systems 5046612 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 1809 for 32-bit Systems 5046615 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 1809 for x64-based Systems 5046615 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 21H2 for 32-bit Systems 5046613 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 21H2 for ARM64-based Systems 5046613 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 21H2 for x64-based Systems 5046613 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 22H2 for 32-bit Systems 5046613 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 22H2 for ARM64-based Systems 5046613 (Security Update) Important Elevation of Privilege Yes
Windows 10 Version 22H2 for x64-based Systems 5046613 (Security Update) Important Elevation of Privilege Yes
Windows 11 Version 22H2 for ARM64-based Systems 5046633 (Security Update) Important Elevation of Privilege Yes
Windows 11 Version 22H2 for x64-based Systems 5046633 (Security Update) Important Elevation of Privilege Yes
Windows 11 Version 23H2 for ARM64-based Systems 5046633 (Security Update) Important Elevation of Privilege Yes
Windows 11 Version 23H2 for x64-based Systems 5046633 (Security Update) Important Elevation of Privilege Yes
Windows 11 Version 24H2 for ARM64-based Systems 5046617 (Security Update) 5046696 (SecurityHotpatchUpdate) Important Elevation of Privilege 5044284 Base: 7.8 Temporal: 6.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C 10.0.26100.2314 10.0.26100.2240 Yes None Windows 11 Version 24H2 for x64-based Systems 5046617 (Security Update) 5046696 (SecurityHotpatchUpdate) Important Elevation of Privilege 5044284 Base: 7.8 Temporal: 6.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C 10.0.26100.2314 10.0.26100.2240 Yes None Windows Server 2008 for 32-bit Systems Service Pack 2 5046661 (Monthly Rollup) 5046639 (Security Only) Important Elevation of Privilege 5044320 Base: 7.8 Temporal: 6.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C 6.0.6003.22966 Yes None Windows Server 2008 for 32-bit Systems Service Pack 2 (Server Core installation) 5046661 (Monthly Rollup) 5046639 (Security Only) Important Elevation of Privilege 5044320 Base: 7.8 Temporal: 6.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C 6.0.6003.22966 Yes None Windows Server 2008 for x64-based Systems Service Pack 2 5046661 (Monthly Rollup) 5046639 (Security Only) Important Elevation of Privilege 5044320 Base: 7.8 Temporal: 6.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C 6.0.6003.22966 Yes None Windows Server 2008 for x64-based Systems Service Pack 2 (Server Core installation) 5046661 (Monthly Rollup) 5046639 (Security Only) Important Elevation of Privilege 5044320 Base: 7.8 Temporal: 6.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C 6.0.6003.22966 Yes None Windows Server 2008 R2 for x64-based Systems Service Pack 1 5046687 (Monthly Rollup) 5046705 (Security Only) Important Elevation of Privilege 5044356 Base: 7.8 Temporal: 6.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C 6.1.7601.27415 Yes None Windows Server 2008 R2 for x64-based Systems Service Pack 1 (Server Core installation) 5046687 (Monthly Rollup) 5046705 (Security Only) Important Elevation of Privilege 5044356 Base: 7.8 Temporal: 6.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C 6.1.7601.27415 Yes None Windows Server 2012 5046697 (Monthly Rollup) Important Elevation of Privilege Yes
Windows Server 2012 (Server Core installation) 5046697 (Monthly Rollup) Important Elevation of Privilege Yes
Windows Server 2012 R2 5046682 (Monthly Rollup) Important Elevation of Privilege Yes
Windows Server 2012 R2 (Server Core installation) 5046682 (Monthly Rollup) Important Elevation of Privilege Yes
Windows Server 2016 5046612 (Security Update) Important Elevation of Privilege Yes
Windows Server 2016 (Server Core installation) 5046612 (Security Update) Important Elevation of Privilege Yes
Windows Server 2019 5046615 (Security Update) Important Elevation of Privilege Yes
Windows Server 2019 (Server Core installation) 5046615 (Security Update) Important Elevation of Privilege Yes
Windows Server 2022 5046616 (Security Update) 5046698 (SecurityHotpatchUpdate) Important Elevation of Privilege 5044281 Base: 7.8 Temporal: 6.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C 10.0.20348.2849 10.0.20348.2819 Yes None Windows Server 2022 (Server Core installation) 5046616 (Security Update) 5046698 (SecurityHotpatchUpdate) Important Elevation of Privilege 5044281 Base: 7.8 Temporal: 6.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C 10.0.20348.2849 10.0.20348.2819 Yes None Windows Server 2022, 23H2 Edition (Server Core installation) 5046618 (Security Update) Important Elevation of Privilege Yes

Patches

8 patches
Article Type Restart
5046665 Security Update Yes
5046612 Security Update Yes
5046615 Security Update Yes
5046613 Security Update Yes
5046633 Security Update Yes
5046697 Monthly Rollup Yes
5046682 Monthly Rollup Yes
5046618 Security Update Yes

Patch Diff

ghidriff · tapisrv.dll ()

Heap OOB read/write in tapisrv.dll GetPriorityList due to missing null terminator validation on user-controlled registry value. GetPriorityListTReqCall reads HKCU\...\Telephony\HandOffPriorities\RequestMakeCall and passes unterminated string to _wcsupr() which reads/writes past heap allocation in svchost.exe (SYSTEM). Secondary info leak via lstrlenW() in SetPriorityList writes heap pointers back to registry. Trigger: write REG_BINARY without null terminator + TAPI RPC call (LSetAppPriority, opnum 69).

Pre-patch version 10.0.22621.4317
Post-patch version 10.0.22621.4530
Function Address Change Note
GetPriorityList code (null terminator validation added) Missing null terminator validation on REG_SZ value read via RegQueryValueExW. _wcsupr() reads/writes past heap allocation. Patch replaces RegQueryValueExW with RegGetValueW which auto-appends null terminators for string values.
SetPriorityList info leak site lstrlenW() on unterminated buffer reads past allocation into adjacent heap chunks. RegSetValueExW writes leaked data (including heap pointers) back to registry. Secondary info leak enables ASLR bypass.
GetPriorityListTReqCall caller Opens HKCU\...\Telephony\HandOffPriorities and calls GetPriorityList with RequestMakeCall value name. Entry point from RPC dispatcher via LSetAppPriority (opnum 69).
View full diff report View RCA report Download PoC

Attack Path

Heap OOB read/write in the Telephony Service from an unterminated registry string the caller owns

Attack path for CVE-2024-43626 Heap OOB read/write in the Telephony Service from an unterminated registry string the caller owns 01 — ENTRY Standard user writes a value under their own HKCU hive HKCU\...\Telephony\HandOffPriorities\RequestMakeCall. The key is user-writable by design; tapisrv reads it while running as SYSTEM inside svchost. 02 — CONTROLLED INPUT The value is written as REG_BINARY with no terminating null RegQueryValueExW returns the bytes verbatim - the API does not append a terminator for non-string types. 03 — PATH A TAPI RPC call drives the priority-list read LSetAppPriority (opnum 69) -> GetPriorityListTReqCall -> GetPriorityList, which passes the buffer to _wcsupr(). 04 — MISSING CHECK No null-terminator validation on the value read from the registry _wcsupr() walks until it finds a terminator, reading and writing uppercase conversions past the heap allocation. The patch replaces RegQueryValueExW with RegGetValueW, which appends terminators for string values. 05 — PRIMITIVE Heap OOB read and write in a SYSTEM process, plus an info leak back to the registry SetPriorityList calls lstrlenW() on the same unterminated buffer and RegSetValueExW writes the over-read data - including heap pointers - back into the attacker-readable registry, giving an ASLR bypass alongside the corruption.

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

Acknowledgments

Chen Le Qi

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