Windows Telephony Service: Heap-based buffer overflow leads to privilege escalation
Summary
A heap-based buffer overflow in the Windows Telephony Service allows an authorized local user to elevate privileges. The attack requires physical access to the device and a valid low-privilege account, and no user interaction. Successful exploitation would give the attacker high impact on confidentiality, integrity and availability, according to the CVSS vector.
Affected
- Windows 10 Version 1607 (builds before 10.0.14393.9688)
- Windows 10 Version 1809 (builds before 10.0.17763.9487)
- Windows 10 Version 21H2 (builds before 10.0.19044.7846)
- Windows 10 Version 22H2 (builds before 10.0.19045.7846)
- Windows 11 Version 23H2 (builds before 10.0.22631.7711)
- Windows Server 2016, including Server Core (builds before 10.0.14393.9688)
- Windows Server 2019, including Server Core (builds before 10.0.17763.9487)
- Windows Server 2022 (builds before 10.0.20348.5870)
Fixed in
Install the November 2026 security updates for the affected Windows versions (fixed builds listed above). Check the MSRC Security Update Guide for the KB numbers.
Workaround
No vendor-published workaround known.
- Keep devices physically secured.
- Enable full-disk encryption (e.g. BitLocker).
- Enforce screen locks and limit local logons on shared machines.
Exploitation
- Microsoft assesses exploitation as not automatable, and no exploitation in the wild is known at the time of publication.
- No public proof of concept is known at the time of publication.
Our recommendation
- Apply the November 2026 cumulative updates as part of the normal monthly patch cycle, with higher priority for shared, unattended or easily accessible devices.
- Apply the physical and access measures listed above until the patch is installed.
- Check the MSRC advisory and CISA KEV for changes in exploitation status.
Information from Microsoft (Patch Tuesday November 2026)
- Severity (Microsoft)
- Important
- Impact
- Elevation of privilege – Windows Telephony Service
- Status on Patch Tuesday
- Neither exploited nor publicly disclosed
- Exploitability assessment
- Exploitation less likely
- Product family
- Windows, Windows ESU (Extended Security Updates)
- Updates (KB)
- KB5131291, KB5131085, KB5131096, KB5131090, KB5131087
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Microsoft Security Update Guide: CVE-2026-116700 msrc.microsoft.com
- CVE Record: CVE-2026-116700 www.cve.org
- Star Labs advisory on the same component (CVE-2024-43626, different CVE) starlabs.sg
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 11 Nov 2026, 11:45.
Original description (NVD)
Heap-based buffer overflow in Windows Telephony Service allows an authorized attacker to elevate privileges with a physical attack.
NVD references (1)
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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