Microsoft Security Response CenterCVE-2026-81963

Windows Update Stack Elevation of Privilege Vulnerability

Improper link resolution before file access ('link following') in Windows Update Stack allows an authorized attacker to elevate privileges locally.

Read the vendor bulletin Get alerts for Windows Server 2025 (Server Core installation)

7.8CVSS out of 10High severity

Scope

What the vendor says is affected

Windows Server 2025 (Server Core installation)
Windows 11 Version 25H2 for ARM64-based Systems
Windows 11 Version 25H2 for x64-based Systems
Windows 11 Version 23H2 for ARM64-based Systems
Windows 11 Version 23H2 for x64-based Systems
Windows 11 Version 24H2 for ARM64-based Systems
Windows 11 Version 24H2 for x64-based Systems
Windows Server 2025
Windows 11 version 26H1 for x64-based Systems
Windows 11 Version 26H1 for ARM64-based Systems

Versions the vendor lists as fixed

10.0.26100.33438
10.0.26200.9445
10.0.22631.7582
10.0.26100.9445
10.0.28000.2954

Next step

What the vendor recommends

Install KB5122871. Install KB5124008. Install KB5122880. Install KB5124012.

Review the complete instructions on the vendor's site

Update history

What changed in later vendor updates

SecurityAlert records field-level changes from the point we begin following a bulletin. Earlier vendor changes may not have a field-by-field record.

Sep 11, 2026 at 8:15 PM UTC
- The vendor changed the advisory's last-updated date.

Timeline

When this advisory changed

Sep 8, 2026 at 7:00 AM UTC
Published by Microsoft Security Response Center
The publication date reported by the vendor.
Sep 8, 2026 at 7:15 PM UTC
Added to SecurityAlert
We collected the advisory from the official source.
Sep 11, 2026 at 7:00 AM UTC
Updated by Microsoft Security Response Center
The vendor changed the advisory after it was first published.
Sep 13, 2026 at 2:40 AM UTC
Confirmed at the source
Our collector saw this advisory during a later source check.

Vulnerabilities

CVEs named in this advisory

CVE-2026-81963View CVSS, KEV, EPSS, and threat context

Source

Start with the vendor's bulletin

SecurityAlert organizes the fields the vendor published. The original bulletin remains the source of record for affected versions, fixes, and later changes.

Vendor: Microsoft Security Response Center
Advisory ID: CVE-2026-81963
Last source check: Sep 13, 2026 at 2:40 AM UTC

Open the official bulletin How SecurityAlert builds this record

Your environment

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Test the update or mitigation through your normal change process.

Watch Windows Server 2025 (Server Core installation)

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What the vendor says is affected

Versions the vendor lists as fixed

What the vendor recommends

What changed in later vendor updates

When this advisory changed

CVEs named in this advisory

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