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CVE-2026-20839 Microsoft CVE debrief

AI-assisted PatchSiren debrief based on the supplied source corpus. The CVE record for CVE-2026-20839 was published on 2026-01-13T18:16:12.320Z and has not been modified since then. CVE-2026-20839 is a medium-severity vulnerability in Windows Client-Side Caching (CSC) Service due to improper access control. An authorized attacker can exploit this vulnerability to disclose information locally. The vulnerability has a CVSS score of 5.5 and affects various versions of Windows 10, Windows 11, and Windows Server. Organizations should assess exposure and implement recommended actions. Microsoft has provided a vendor advisory for mitigation.

Vendor
Microsoft
Product
Windows 10 Version 1607
CVSS
MEDIUM 5.5
CISA KEV
Not listed in stored evidence
Original CVE published
2026-01-13
Original CVE updated
2026-07-30
Advisory published
2026-01-13
Advisory updated
2026-07-30

Who should care

Organizations using affected versions of Windows 10, Windows 11, and Windows Server should prioritize patching or mitigating CVE-2026-20839. IT administrators, cybersecurity teams, and vulnerability management professionals should assess exposure and implement recommended actions.

Technical summary

CVE-2026-20839 is a medium-severity vulnerability in Windows Client-Side Caching (CSC) Service due to improper access control. An authorized attacker can exploit this vulnerability to disclose information locally. The vulnerability has a CVSS score of 5.5 and affects various versions of Windows 10, Windows 11, and Windows Server.

Defensive priority

Medium-priority defensive tasks are recommended given the local information disclosure risk and medium CVSS score.

Recommended defensive actions

  • Inventory and assess Windows systems for exposure to CVE-2026-20839, focusing on systems with Client-Side Caching (CSC) Service enabled.
  • Apply vendor-recommended mitigations or patches for CVE-2026-20839 as available.
  • Monitor system logs for suspicious activity related to the CSC Service.
  • Implement compensating controls such as restricting access to sensitive information and enforcing least privilege principles.
  • Consider temporary disabling of the CSC Service if immediate patching is not feasible.

Evidence notes

The CVE-2026-20839 record indicates improper access control in Windows Client-Side Caching (CSC) Service, allowing an authorized attacker to disclose information locally. Microsoft has provided a vendor advisory for mitigation.

Official resources

AI-assisted PatchSiren debrief based on the supplied source corpus. The CVE record was published on 2026-01-13T18:16:12.320Z and has not been modified since then.