CVE-2026-81963

Windows Update Stack Elevation of Privilege Vulnerability

Actively exploited (CISA KEV) High 7.8 CVSS 3.1

Description

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

Description as published by the source, in English.

Key facts

Published: 2026-09-08
Last modified: 2026-09-18
Assigned by: microsoft
CVSS 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
Scored by: CVE Program
Fix available: Yes, see references

Actively exploited

CISA added this vulnerability to the Known Exploited Vulnerabilities catalogue on 2026-09-08, with a remediation deadline of 2026-09-22 for US federal agencies.

Required action: Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.

Affected products

Vendor	Product	Versions	Status
Microsoft	Windows 11 version 23H2 (ARM64-based Systems)	≥ 10.0.22631.0, < 10.0.22631.7582	Affected
Microsoft	Windows 11 Version 24H2 (ARM64-based Systems)	≥ 10.0.26100.0, < 10.0.26100.9445	Affected
Microsoft	Windows 11 Version 25H2 (ARM64-based Systems)	≥ 10.0.26200.0, < 10.0.26200.9445	Affected
Microsoft	Windows 11 version 26H1 (ARM64-based Systems)	≥ 10.0.28000.0, < 10.0.28000.2954	Affected
Microsoft	Windows Server 2025 (x64-based Systems)	≥ 10.0.26100.0, < 10.0.26100.33438	Affected
Microsoft	Windows Server 2025 (Server Core installation) (x64-based Systems)	≥ 10.0.26100.0, < 10.0.26100.33438	Affected

Weakness type

CWE-284: Improper Access Control
The product does not restrict or incorrectly restricts access to a resource from an unauthorized actor.
CWE-59: Improper Link Resolution Before File Access ('Link Following')
The product attempts to access a file based on the filename, but it does not properly prevent that filename from identifying a link or shortcut that resolves to an unintended resource.

Attack techniques

Derived through the weakness type: CVE to CWE to CAPEC to ATT&CK. This shows which techniques the weakness class is historically used for. It does not assert that this vulnerability has been exploited that way.

T1014: Rootkit stealth
T1027.006: HTML Smuggling stealth
T1027.009: Embedded Payloads stealth
T1037: Boot or Logon Initialization Scripts persistence, privilege-escalation
T1080: Taint Shared Content lateral-movement
T1505.005: Terminal Services DLL persistence
T1542.003: Bootkit stealth, persistence
T1543: Create or Modify System Process persistence, privilege-escalation
T1543.001: Launch Agent persistence, privilege-escalation
T1543.003: Windows Service persistence, privilege-escalation
T1543.004: Launch Daemon persistence, privilege-escalation
T1546.001: Change Default File Association privilege-escalation, persistence
T1546.004: Unix Shell Configuration Modification privilege-escalation, persistence
T1546.008: Accessibility Features privilege-escalation, persistence
T1546.016: Installer Packages privilege-escalation, persistence
T1547: Boot or Logon Autostart Execution persistence, privilege-escalation
T1547.006: Kernel Modules and Extensions persistence, privilege-escalation
T1547.009: Shortcut Modification persistence, privilege-escalation
T1553.004: Install Root Certificate defense-impairment
T1556.006: Multi-Factor Authentication defense-impairment, persistence, credential-access

References

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-81963 vendor-advisory, patch

Related at Berigo

Articles

New exploit is said to grant SYSTEM through Microsoft Defender Same product 2026-08-14
On 12 August 2026 the researcher known as Nightmare Eclipse released exploit code called ShieldBreak, said to grant SYSTEM privileges through Microso…

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Sources and freshness

CVE

What it is: A reference number naming one specific vulnerability, for example CVE-2024-9474.
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Used with the others: The number is the key. NVD, KEV and EPSS all describe the same CVE.

NVD CWE CISA KEV EPSS

How to read this together

No single value should be used on its own. A high CVSS score does not mean a vulnerability is being exploited, and a low one does not mean it is harmless. The four sources answer four different questions.

CVE names the specific vulnerability.
NVD adds severity and technical detail about it.
CWE describes the type of mistake behind it.
CISA KEV shows that it is already being exploited.
EPSS estimates how likely exploitation is soon.

The order that decides what is urgent

Do you actually have the product?
Is the version you run affected?
Is it listed in CISA KEV?
Does it have a high EPSS score?
Is the system reachable from the internet or from others?
How important is the system to the business?
Are there compensating controls already in place?

The first two questions are not about the vulnerability at all. They are about you, and they remove most of the list before you start.

A short example

Fix this week

CVSS 6,5 (medium)

In CISA KEV: yes
EPSS: 94 per cent
A firewall facing the internet

Can be scheduled

CVSS 9,8 (critical)

In CISA KEV: no
EPSS: 0,04 per cent
A test server with no internet access

Sorted by CVSS alone, the one on the right comes first. It is the more serious flaw in theory. But the one on the left is being used against real organisations right now, and it sits where an attacker can reach it. That is the one to fix first.

The critical one still has to be fixed. It just does not have to be fixed today.

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