Severity by source
AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Local authenticated access (AV:L/PR:L); AC:H because a use-after-free race must be won for reliable exploitation; full SYSTEM compromise gives C:H/I:H/A:H.
Primary rating from NVD.
CVSS VectorNVD
Lifecycle Timeline
2DescriptionCVE.org
Use after free in Windows Telephony Service allows an authorized attacker to elevate privileges locally.
AnalysisAI
Local privilege escalation in the Windows Telephony Service (TAPI) affects a broad range of Windows client and server releases, from Windows 10 1607 and Server 2012 through Windows 11 26H1 and Server 2025. An authenticated local attacker can exploit a use-after-free (CWE-416) memory-corruption flaw to gain SYSTEM-level privileges; there is no public exploit identified at time of analysis and EPSS is very low (0.04%), but the CVSS 3.1 base score is 7.8 with total technical impact per CISA SSVC.
Technical ContextAI
The Windows Telephony Service implements the Telephony API (TAPI), a legacy Windows subsystem that mediates access to modems, telephony hardware, VoIP and call-control functions for user applications. The root cause is CWE-416 (Use After Free): the service references a heap object after it has been freed, allowing an attacker who can influence allocation/free timing to reclaim the freed memory with attacker-controlled data and corrupt program state. Because the service runs with elevated (SYSTEM) privileges while accepting requests from lower-privileged local callers, successful memory corruption translates directly into privilege elevation. CPE data confirms the affected component spans Microsoft Windows 10 (1607, 1809, 21H2, 22H2), Windows 11 (22H3, 23H2, 24H2, 25H2, 26H1) and Windows Server (2012, 2012 R2, 2016, 2019, 2022, 2022 23H2, 2025).
RemediationAI
Vendor-released patch: apply the Microsoft security update that raises each affected OS to at least the fixed build listed above (e.g., Windows 11 24H2 to 10.0.26100.8457, Server 2022 to 10.0.20348.5139, Windows 10 22H2 to 10.0.19045.7291) via the standard monthly cumulative update; consult https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-34338 for the exact KB per platform. Because exploitation requires local authenticated access to the Telephony Service, a compensating control where immediate patching is not possible is to stop and disable the Telephony service (TapiSrv) - this closes the attack surface but will break TAPI-dependent applications such as dial-up/RAS clients, some fax and modem software, and legacy CTI/VoIP integrations, so validate dependencies first. General EoP hardening (least-privilege accounts, restricting interactive/local logon, EDR monitoring for anomalous SYSTEM token acquisition) reduces the population of attackers who can reach the service. Prioritize patching multi-user and shared hosts (RDS/Citrix, terminal servers) where untrusted low-privileged users can run code locally.
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Same weakness CWE-416 – Use After Free
View allSame technique Denial Of Service
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External POC / Exploit Code
Leaving vuln.today
EUVD-2026-29597
GHSA-wjp8-23w4-8hcj