Authenticated privilege escalation via unrestricted path write
Published Jan 13, 2026 · Updated Jan 13, 2026
Path control in Microsoft Windows Telephony Service allows remote authenticated users to elevate privileges over an adjacent network. The service accepts a caller-supplied output path without verifying that it names a mailslot, permitting arbitrary writes to files writable by Network Service. Low-privileged access can rewrite tsec.ini, grant Telephony Service administrator rights, and cause the service to load attacker-controlled code.
Summary
What happened
Path control in Microsoft Windows Telephony Service allows remote authenticated users to elevate privileges over an adjacent network. The service accepts a caller-supplied output path without verifying that it names a mailslot, permitting arbitrary writes to files writable by Network Service. Low-privileged access can rewrite tsec.ini, grant Telephony Service administrator rights, and cause the service to load attacker-controlled code.
The record
- CVE
- CVE-2026-20931
- Published
- Jan 13, 2026
- Updated
- Jan 13, 2026
- Vendor
- Microsoft
- Product
- Windows Server 2019
- Classifications
- CWE-73, T1068
- Attack vector
- adjacent
- Privileges
- authenticated
Timeline
How it unfolded
- Jan 13, 2026CVE publishedPublication date reported by the CVE source.
- Jan 13, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=10.0.17763.0 <10.0.17763.8276
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- Windows Telephony Service tsec.ini overwrite demonstrationfunctional · demonstrated
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Technologies
Your stack
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Your stack
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