CriticalCVE-2026-81963

Windows Update Stack Elevation of Privilege Vulnerability (CVE-2026-81963)

Published 08.09.2026Last modified 09.09.2026In CISA KEV since 08.09.2026Sources: CVE.org, Msrc Update Guide, pwn.watch, BSI

What is affected, what to do

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

The vulnerability is being actively exploited; treat it as a priority. Update Microsoft Windows 11 version 23H2 to version 10.0.22631.7582, Microsoft Windows 11 Version 24H2 to version 10.0.26100.9445, Microsoft Windows 11 Version 25H2 to version 10.0.26200.9445. Immediate actions, mitigation and detection rules are in the runbook below.

Affected: Microsoft Windows 11 version 23H2 lt 10.0.22631.0..10.0.22631.7582
Microsoft Windows 11 Version 24H2 lt 10.0.26100.0..10.0.26100.9445
Microsoft Windows 11 Version 25H2 lt 10.0.26200.0..10.0.26200.9445
Microsoft Windows 11 version 26H1 lt 10.0.28000.0..10.0.28000.2954
Microsoft Windows Server 2025 lt 10.0.26100.0..10.0.26100.33438
Microsoft Windows Server 2025 (Server Core installation) lt 10.0.26100.0..10.0.26100.33438
Fixed in: Microsoft Windows 11 version 23H2 10.0.22631.7582
Microsoft Windows 11 Version 24H2 10.0.26100.9445
Microsoft Windows 11 Version 25H2 10.0.26200.9445
Microsoft Windows 11 version 26H1 10.0.28000.2954
Microsoft Windows Server 2025 10.0.26100.33438
Microsoft Windows Server 2025 (Server Core installation) 10.0.26100.33438

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Metrics

7.8

Priority

XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

Source: NVD, CVSS v3

7.8

CVSS v3

Severity High on the scale from 0 to 10.

Source: CVE.org, Msrc Update Guide, pwn.watch, BSI

0.4 %

EPSS score

Low — model estimates < 1% exploitation likelihood.

Source: FIRST EPSS, percentile 33.3

Show all metrics

Severity: Critical
Priority (0–325) The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first? Read in glossary: 174.28 Methodology
Exploit maturity An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack. Read in glossary: actively exploitedSource: VulnCheck KEV (opens in a new tab) How we classify
XIEM Effective CVSS XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command. Read in glossary: 7.8 Methodology
CVSS v3 CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions. Read in glossary: 7.8
EPSS score The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“. Read in glossary: 0.4 %; Low — model estimates < 1% exploitation likelihood.
EPSS percentile The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking. Read in glossary: 33.3; Elevated — this CVE ranks above at least 10% of all CVEs scored today.
KEV status The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching. Read in glossary: Actively exploited
Published: 08.09.2026
In CISA KEV since The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching. Read in glossary: 08.09.2026
CWE CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect. Read in glossary: CWE-59, CWE-284

Response and mitigation

Why act now?

Prioritisation rationale

This CVE is on KEV because link-following flaws in the Windows Update Stack are a reliable local privilege escalation to SYSTEM and slot cleanly into post-exploitation chains after phishing or loader infections. The CVSS vector describes local, low-privilege access with no user interaction — any standard user already on the box can start the chain, which multiplies the impact on multi-user hosts. The exploitation likelihood is currently moderate and CISA has not flagged ransomware use, but the primitive is attractive enough to be bundled into commodity post-exploitation toolkits quickly. Patch in exposure order: RDS and VDI first, shared workstations next, single-user laptops in the normal patch wave, isolated OT clients at the next maintenance window.

01
Runbook step 1
Immediate response (0-24 h)
- Deploy the Microsoft Patch Tuesday update for the affected Windows 11 builds: 23H2 above 10.0.22631.7582, 24H2 above 10.0.26100.9445, 25H2 above 10.0.26200.9445, 26H1 above 10.0.28000.2954. Push via WSUS/Intune with a 72-hour deadline and enforced reboot.
- Prioritise multi-user systems (RDS hosts, VDI pools, jump servers, developer workstations); the bug requires local authentication, so shared-login hosts are the realistic abuse surface.
- Until patched, set the Windows Update service (wuauserv) to Manual on highly exposed endpoints (kiosks, shared workstations) and enable it only during maintenance windows; log an exception so update compliance is tracked by another control in the meantime.
- Review and shrink local Administrators and Power Users group membership on unmanaged endpoints (net localgroup Administrators); every removed local account reduces the usable attacker starting pool for this EoP.
- Verify snapshot and backup status for affected file servers and critical clients — a successful EoP is typically the pivot into LSASS credential dumping and lateral movement.
02
Runbook step 2
Mitigation layers
- Endpoint hardening: enforce AppLocker/WDAC policies that block execution of unsigned binaries from %TEMP%, %LOCALAPPDATA% and other user-writable paths, which is the usual drop location for EoP PoCs before they trigger the update-stack logic.
- IAM / least privilege: deploy LAPS everywhere, keep standard users off the local Administrators group, migrate service accounts to gMSAs so a compromised user context cannot immediately be levered to SYSTEM.
- Filesystem hardening: audit ACLs on directories consumed by the Windows Update Stack (C:\Windows\SoftwareDistribution, C:\Windows\WinSxS\Temp); find and remove any non-admin writable paths. Link-following bugs are almost always exploited via junctions/symlinks planted in such paths.
- Restrict symlink creation: use Group Policy to grant SeCreateSymbolicLinkPrivilege to Administrators only (Computer Configuration → Windows Settings → Security Settings → Local Policies → User Rights Assignment).
- EDR policy: move child processes of TrustedInstaller.exe, TiWorker.exe, wuauclt.exe, UsoClient.exe and svchost.exe -k netsvcs into a high-sensitivity monitoring bucket; block or queue for review any spawns of cmd, powershell, rundll32.
- Network segmentation: put admin workstations into a dedicated Tier-0/Tier-1 VLAN, restrict SMB and WinRM from standard clients to servers via host firewall to slow lateral movement after a successful local EoP.
03
Runbook step 3
Detection rules
- Sysmon EID 11 (FileCreate) and EID 2 (FileCreationTimeChanged) on paths under C:\Windows\SoftwareDistribution\* or C:\Windows\Temp\* correlated with a parent of TiWorker.exe/TrustedInstaller.exe but a non-SYSTEM initiating user token — the classic link-following signature.
- Sysmon EID 1 (ProcessCreate): KQL shape — DeviceProcessEvents | where InitiatingProcessFileName in~ ("TiWorker.exe","wuauclt.exe","UsoClient.exe","TrustedInstaller.exe") and FileName in~ ("cmd.exe","powershell.exe","rundll32.exe","regsvr32.exe").
- Windows Security EID 4663 (object access) combined with EID 4656 on objects of type SymbolicLink / Junction inside update directories; Sigma shape: EventID: 4663 + ObjectName contains \\SoftwareDistribution\\ + AccessMask: 0x40000 (DELETE) by a non-SYSTEM process.
- EDR heuristic: SYSTEM-context processes appearing immediately after a successful Windows Update cycle while running from a user-SID working directory — indicator of token theft via the update stack.
- Baseline alert on sudden growth of local admin group: Windows EID 4732 (A member was added to a security-enabled local group) targeting Administrators without a matching approved change ticket.

Detection rules

No NEOSEC detection rule is available for this vulnerability yet.

Classification under NIS2 and CRA

Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

NIS2 NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management. Read in glossary: Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).
CRA The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates. Read in glossary: Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.
ISO/IEC 27001 ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security. Read in glossary: Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

Description

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

Source: cvelistv5, NVD (NIST), CVE.org (MITRE), CISA KEV Catalog, Microsoft Security Update Guide, pwn.watch, BSI CSAF, BSI WID Portal

Affected products

The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

Affected products
		Affected versions	Fixed in
Microsoft	Windows 11 version 23H2	`10.0.22631.0 – < 10.0.22631.7582`	`10.0.22631.7582`
Microsoft	Windows 11 Version 24H2	`10.0.26100.0 – < 10.0.26100.9445`	`10.0.26100.9445`
Microsoft	Windows 11 Version 25H2	`10.0.26200.0 – < 10.0.26200.9445`	`10.0.26200.9445`
Microsoft	Windows 11 version 26H1	`10.0.28000.0 – < 10.0.28000.2954`	`10.0.28000.2954`
Microsoft	Windows Server 2025	`10.0.26100.0 – < 10.0.26100.33438`	`10.0.26100.33438`
Microsoft	Windows Server 2025 (Server Core installation)	`10.0.26100.0 – < 10.0.26100.33438`	`10.0.26100.33438`

Vendors and products

Affected operating systems

Affected operating systems

Windows	microsoft	windows_11_23h2	—
Windows	microsoft	windows_11_24h2	—
Windows	microsoft	windows_11_25h2	—
Windows	microsoft	windows_11_26h1	—
Windows	microsoft	windows_server_2025	—

Weakness classes (CWE)

CWE-59Improper Link Resolution Before File Access ('Link Following')
Base
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.
Entry at MITRE CWE-59
CWE-284Improper Access Control
Pillar
The product does not restrict or incorrectly restricts access to a resource from an unauthorized actor.
Entry at MITRE CWE-284

Public exploit references

Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.

Public exploit references

CISA KEV Catalog	CISA Known Exploited Vulnerability (opens in a new tab)cisa.gov	actively exploited	08.09.2026

References & sources

Microsoft Security Update GuideWindows Update Stack Elevation of Privilege VulnerabilityVendor advisory, Patch
cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2026-81963government-resource
pwn.watchpwn.watch: Microsoft Windows: Microsoft Windows Link Following Vulnerabilitypwn-watch
Microsoft Security Update GuideMicrosoft Windows — CVE-2026-81963pwn-watch
NVD (NIST)NVD: CVE-2026-81963pwn-watch
Microsoft Security Update GuideMicrosoft Windows — CVE-2026-85880pwn-watch
NVD (NIST)NVD: CVE-2026-85880pwn-watch
cisa.govCISA Known Exploited Vulnerabilities Catalogpwn-watch
JPCERT/CCJPCERT/CC JPCERT-AT-2026-0025: Microsoft Releases September 2026 Security Updatesjpcert

Changes to this CVE

Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

09.09.2026Record modifiedCISA ADP

CISA assessment (SSVC): exploitation: active, automatable: no

Show the original change

Individual changes of this event as published by NVD
Type	Action	Before	After
SSVC assessment	changed	{"id":"CVE-2026-81963","role":"CISA Coordinator","options":[{"exploitation":"active"},{"automatable":"no"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-09-08T18:44:08.999075Z"}	{"id":"CVE-2026-81963","role":"CISA Coordinator","options":[{"exploitation":"active"},{"automatable":"no"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-09-07T00:00:00+00:00"}

Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

08.09.2026Initial analysis by NVDNVD

Newly listed as affected:

Microsoft Windows Server 2025 (before 10.0.26100.33438)
Microsoft Windows 11 23H2 (before 10.0.22631.7582)
Microsoft Windows 11 24H2 (before 10.0.26100.9445)
Microsoft Windows 11 25H2 (before 10.0.26200.9445)
Microsoft Windows 11 26H1 (before 10.0.28000.2954)

New references:

Show 3 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Product configuration	added	—	OR cpe:2.3:o:microsoft:windows_server_2025::::::::* versions up to (excluding) 10.0.26100.33438 cpe:2.3:o:microsoft:windows_11_23h2:::::::arm64: versions up to (excluding) 10.0.22631.7582 cpe:2.3:o:microsoft:windows_11_23h2:::::::x64: versions up to (excluding) 10.0.22631.7582 cpe:2.3:o:microsoft:windows_11_24h2:::::::arm64: versions up to (excluding) 10.0.26100.9445 cpe:2.3:o:microsoft:windows_11_24h2:::::::x64: versions up to (excluding) 10.0.26100.9445 cpe:2.3:o:microsoft:windows_11_25h2:::::::arm64: versions up to (excluding) 10.0.26200.9445 cpe:2.3:o:microsoft:windows_11_25h2:::::::x64: versions up to (excluding) 10.0.26200.9445 cpe:2.3:o:microsoft:windows_11_26h1:::::::arm64: versions up to (excluding) 10.0.28000.2954 cpe:2.3:o:microsoft:windows_11_26h1:::::::x64: versions up to (excluding) 10.0.28000.2954
Reference type	added	—	Microsoft Corporation: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-81963 Types: Patch, Vendor Advisory
Reference type	added	—	CISA-ADP: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-81963 Types: US Government Resource

Source identifier: nvd@nist.gov

08.09.2026Record modifiedCISA ADP

CISA assessment (SSVC): exploitation: active, automatable: no

New references:

https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-81963

Show 2 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Reference	added	—	https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-81963
SSVC assessment	changed	{"id":"CVE-2026-81963","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"no"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-09-08T17:40:01.139617Z"}	{"id":"CVE-2026-81963","role":"CISA Coordinator","options":[{"exploitation":"active"},{"automatable":"no"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-09-08T18:44:08.999075Z"}

Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

08.09.2026CISA KEV entry updated9119a7d8…
4 individual changes: Date Added, Due Date, Required Action, Vulnerability Name
Show 4 original changes
Individual changes of this event as published by NVD
Type Action Before After
Date Added added
—
2026-09-08
Due Date added
—
2026-09-08
Required Action added
—
2026-09-08
Vulnerability Name added
—
2026-09-08
Source identifier: 9119a7d8-5eab-497f-8521-727c672e3725

Individual changes of this event as published by NVD
Type	Action	Before	After
Date Added	added	—	2026-09-08
Due Date	added	—	2026-09-08
Required Action	added	—	2026-09-08
Vulnerability Name	added	—	2026-09-08

08.09.2026ReceivedMicrosoft

CVSS V3.1: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Weakness type: CWE-59, CWE-284

Description added or changed

New references:

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

Show 6 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Description	added	—	Improper link resolution before file access ('link following') in Windows Update Stack allows an authorized attacker to elevate privileges locally.
CVSS	added	—	AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Weakness type (CWE)	added	—	CWE-59
Weakness type (CWE)	added	—	CWE-284
Affected versions (publisher)	added	—	New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/81xxx/CVE-2026-81963.json">CVE-2026-81963</a>
Reference	added	—	https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-81963

Source identifier: secure@microsoft.com

Show one older change

08.09.2026Record modifiedCISA ADP

CISA assessment (SSVC): exploitation: none known, automatable: no

Show the original change

Individual changes of this event as published by NVD
Type	Action	Before	After
SSVC assessment	added	—	{"id":"CVE-2026-81963","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"no"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-09-08T17:40:01.139617Z"}

Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

Linked advisories

Microsoft Patchday September 2026: 974 Schwachstellen, zwei aktiv ausgenutztNEOSEC article11.09.2026
NCSC-2026-0353 [1.01] [M/H] Kwetsbaarheden verholpen in Microsoft WindowsNCSC-NL09.09.2026
September 2026 Patch Tuesday roundup: Plugs for two zero day holes among almost 1,000 fixes in WindowsCSO Online09.09.2026
Multiples vulnérabilités dans Microsoft Windows (09 septembre 2026)CERT-FR (ANSSI)09.09.2026

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<a href="https://intel.neosec.eu/en/cve/CVE-2026-81963"><img src="https://intel.neosec.eu/badge/cve/CVE-2026-81963.svg?lang=en" alt="CVE-2026-81963 – NEOSEC Intel" height="20"></a>

What is affected, what to do

Metrics

Response and mitigation

Prioritisation rationale

Immediate response (0-24 h)

Mitigation layers

Detection rules

Detection rules

Classification under NIS2 and CRA

Description

Affected products

Vendors and products

Affected operating systems

Weakness classes (CWE)

Public exploit references

References & sources

Changes to this CVE

Linked advisories