CVE-2021-1661Known exploitation

Local privilege escalation via Windows Installer

Published Jan 12, 2021 · Updated Oct 8, 2024

Windows Installer elevation of privilege in Microsoft Windows releases before the January 2021 security update allows local users to gain SYSTEM privileges. The Windows Installer service mishandles an installation operation, permitting a low-privileged authenticated local user to execute code with elevated rights. Exploitation requires local access and no user interaction; successful attacks can compromise confidentiality, integrity, and availability.

CVSS severity7.8
High
EPSS probability0.82%
Next 30 days · Sep 16, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Windows Installer elevation of privilege in Microsoft Windows releases before the January 2021 security update allows local users to gain SYSTEM privileges. The Windows Installer service mishandles an installation operation, permitting a low-privileged authenticated local user to execute code with elevated rights. Exploitation requires local access and no user interaction; successful attacks can compromise confidentiality, integrity, and availability.

The record

CVE
CVE-2021-1661
Published
Jan 12, 2021
Updated
Oct 8, 2024
Vendor
Microsoft
Product
Windows 10 Version 1507
Classifications
T1068
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Jan 12, 2021CVE publishedPublication date reported by the CVE source.
  2. Nov 24, 2021Exploitation reportedIn-the-wild exploitation reported
  3. Oct 8, 2024Record 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.

  1. Affected versionversion=10.0.0 <publication

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Microsoft · Windows 10 Version 1507version=10.0.0 <publication
Microsoft · Windows Server 2019version=10.0.0 <publication
Microsoft · Windows 7version=6.1.0 <publication
Microsoft · Windows 10 Version 1909version=10.0.0 <publication
Microsoft · Windows 10 Version 1803version=10.0.0 <publication
Microsoft · Windows 8.1version=6.3.0 <publication
Microsoft · Windows Server 2016 (Server Core installation)version=10.0.0 <publication
Microsoft · Windows Server 2012 (Server Core installation)version=6.2.0 <publication
Microsoft · Windows Server 2012version=6.2.0 <publication
Microsoft · Windows Server, version 2004version=10.0.0 <publication
Microsoft · Windows Server 2016version=10.0.0 <publication
Microsoft · Windows Server 2008 R2 Service Pack 1version=6.1.0 <publication
Microsoft · Windows 10 Version 20H2version=10.0.0 <publication
Microsoft · Windows Server 2008 R2 Service Pack 1 (Server Core installation)version=6.0.0 <publication
Microsoft · Windows Server 2012 R2 (Server Core installation)version=6.3.0 <publication
Microsoft · Windows Server 2019 (Server Core installation)version=10.0.0 <publication
Microsoft · Windows 7 Service Pack 1version=6.1.0 <publication
Microsoft · Windows Server version 20H2version=10.0.0 <publication
Microsoft · Windows 10 Version 1607version=10.0.0 <publication
Microsoft · Windows Server 2008 Service Pack 2version=6.0.0 <publication
Microsoft · Windows 10 Version 2004version=10.0.0 <publication
Microsoft · Windows 10 Version 1809version=10.0.0 <publication
Microsoft · Windows Server 2012 R2version=6.3.0 <publication
Microsoft · Windows Server 2008 Service Pack 2 (Server Core installation)version=6.0.0 <publication
Microsoft · Windows Server, version 1909 (Server Core installation)version=10.0.0 <publication

Published CVSS scores

7.8MicrosoftCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/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 exploitationReported
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.

Reported exploitation

Technologies

Your stack

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Your stack

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