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Vulnerability · Published Jan 13, 2026 · Assigned by microsoft

CVE-2026-20839Windows Client-Side Caching (CSC) Service Information Disclosure Vulnerability

Medium 5.5

In plain English

A medium-severity improper access control in Windows 10 Version 1607 from Microsoft. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 41% of all known vulnerabilities).

Severity (CVSS 3.1)5.5Medium
Exploit odds (30 days)0.5%top 58.7% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official description

Improper access control in Windows Client-Side Caching (CSC) Service allows an authorized attacker to disclose information locally.

Affected products (as reported)

VendorProductVersions
Microsoft Windows 10 Version 1607 10.0.14393.0 – before 10.0.14393.8783
Microsoft Windows 10 Version 1809 10.0.17763.0 – before 10.0.17763.8276
Microsoft Windows 10 Version 21H2 10.0.19044.0 – before 10.0.19044.6809
Microsoft Windows 10 Version 22H2 10.0.19045.0 – before 10.0.19045.6809
Microsoft Windows 11 version 23H2 10.0.22631.0 – before 10.0.22631.6491
Microsoft Windows 11 Version 23H2 10.0.22631.0 – before 10.0.22631.6491
Microsoft Windows 11 Version 24H2 10.0.26100.0 – before 10.0.26100.7623
Microsoft Windows 11 Version 25H2 10.0.26200.0 – before 10.0.26200.7623
Microsoft Windows Server 2008 R2 Service Pack 1 6.1.7601.0 – before 6.1.7601.28117
Microsoft Windows Server 2008 R2 Service Pack 1 (Server Core installation) 6.1.7601.0 – before 6.1.7601.28117
Microsoft Windows Server 2012 6.2.9200.0 – before 6.2.9200.25868
Microsoft Windows Server 2012 (Server Core installation) 6.2.9200.0 – before 6.2.9200.25868
Microsoft Windows Server 2012 R2 6.3.9600.0 – before 6.3.9600.22968
Microsoft Windows Server 2012 R2 (Server Core installation) 6.3.9600.0 – before 6.3.9600.22968
Microsoft Windows Server 2016 10.0.14393.0 – before 10.0.14393.8783
Microsoft Windows Server 2016 (Server Core installation) 10.0.14393.0 – before 10.0.14393.8783
Microsoft Windows Server 2019 10.0.17763.0 – before 10.0.17763.8276
Microsoft Windows Server 2019 (Server Core installation) 10.0.17763.0 – before 10.0.17763.8276
Microsoft Windows Server 2022 10.0.20348.0 – before 10.0.20348.4648
Microsoft Windows Server 2022, 23H2 Edition (Server Core installation) 10.0.25398.0 – before 10.0.25398.2092
Microsoft Windows Server 2025 10.0.26100.0 – before 10.0.26100.32230
Microsoft Windows Server 2025 (Server Core installation) 10.0.26100.0 – before 10.0.26100.32230

Weakness: CWE-284 · 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

References