CVE-2021-38634

SYSTEM code execution via directory junction deletion

Published Sep 15, 2021 · Updated Aug 10, 2026

Privilege escalation in Microsoft Windows Update Client allows local users to execute arbitrary code as SYSTEM through a directory junction. Windows Update Agent follows an attacker-created directory junction while performing a privileged deletion, allowing a chosen file to be removed. Exploitation requires prior low-privileged code execution on the host; successful abuse grants SYSTEM execution and can compromise the system.

CVSS severity7.1

High

EPSS probability0.86%

Next 30 days · Sep 16, 2026

Known exploitationUnconfirmed

Based on sourced intelligence

Hinoki checkNot available

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Summary

What happened

The record

CVE: CVE-2021-38634
Published: Sep 15, 2021
Updated: Aug 10, 2026

Vendor: Microsoft
Product: Windows 10 Version 1507
Classifications: T1068

Attack vector: local
Privileges: authenticated

Timeline

How it unfolded

Sep 15, 2021CVE publishedPublication date reported by the CVE source.
Aug 10, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

Affected versionversion=10.0.10240.0 <10.0.10240.19060

What conditions does exploitation require?

Attack vectorlocal

Required privilegesauthenticated

What is affected?

Microsoft · Windows 10 Version 1507version=10.0.10240.0 <10.0.10240.19060

Microsoft · Windows Server 2019version=10.0.17763.0 <10.0.17763.2183

Microsoft · Windows 10 Version 21H1version=10.0.0 <10.0.19043.1237

Microsoft · Windows 10 Version 1909version=10.0.0 <10.0.18363.1801

Microsoft · Windows Server 2016 (Server Core installation)version=10.0.14393.0 <10.0.14393.4651

Microsoft · Windows Server, version 2004version=10.0.0 <10.0.19041.1237

Microsoft · Windows Server 2016version=10.0.14393.0 <10.0.14393.4651

Microsoft · Windows 10 Version 20H2version=10.0.0 <10.0.19042.1237

Microsoft · Windows Server 2019 (Server Core installation)version=10.0.17763.0 <10.0.17763.2183

Microsoft · Windows Server version 20H2version=10.0.0 <10.0.19042.1237

Microsoft · Windows 10 Version 1607version=10.0.14393.0 <10.0.14393.4651

Microsoft · Windows Server 2022version=10.0.20348.0 <10.0.20348.230

Microsoft · Windows 10 Version 2004version=10.0.0 <10.0.19041.1237

Microsoft · Windows 10 Version 1809version=10.0.0 <10.0.17763.2183; version=10.0.17763.0 <10.0.17763.2183

Published CVSS scores

7.1MicrosoftCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026

Latest reporting daySep 16, 2026

Latest daily unique IPsUnavailable

Prior 30-day averageUnavailable

SourceShadowserver honeypots (KEV)

Vectorlocal

Privilegesauthenticated

Known exploitationUnconfirmed

Public exploitUnconfirmed

Weakness, pattern, technique

T1068Exploitation for Privilege Escalation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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