Microsoft Security Response CenterCVE-2026-56155

Active Directory Federation Services Elevation of Privilege Vulnerability

Insufficient granularity of access control in Active Directory Federation Services (AD FS) allows an authorized attacker to elevate privileges locally.

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7.8CVSS out of 10High severity

Scope

What the vendor says is affected

Windows 10 Version 1809 for 32-bit Systems
Windows 10 Version 1809 for x64-based Systems
Windows Server 2019
Windows Server 2019 (Server Core installation)
Windows Server 2022
Windows Server 2025 (Server Core installation)
Windows Server 2025
Windows 10 Version 1607 for 32-bit Systems
Windows 10 Version 1607 for x64-based Systems
Windows Server 2016
Windows Server 2016 (Server Core installation)
Windows Server 2012
Windows Server 2012 (Server Core installation)
Windows Server 2012 R2
Windows Server 2012 R2 (Server Core installation)

Versions the vendor lists as fixed

10.0.17763.9020
10.0.20348.5386
10.0.26100.33158
10.0.14393.9339
6.2.9200.26226
6.3.9600.23291

Next step

What the vendor recommends

Install KB5099538. Install KB5099540. Install KB5099536. Install KB5099535. Install KB5099445. Install KB5099444.

Review the complete instructions on the vendor's site

Timeline

When this advisory changed

Jul 14, 2026 at 7:00 AM UTC
Published by Microsoft Security Response Center
The publication date reported by the vendor.
Sep 28, 2026 at 11:20 AM UTC
Added to SecurityAlert
We collected the advisory from the official source.

Vulnerabilities

CVEs named in this advisory

CVE-2026-56155View CVSS, KEV, EPSS, and threat context

Source

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Vendor: Microsoft Security Response Center
Advisory ID: CVE-2026-56155
Last source check: Sep 28, 2026 at 11:20 AM UTC

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What the vendor says is affected

Versions the vendor lists as fixed

What the vendor recommends

When this advisory changed

CVEs named in this advisory

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