CVE-2021-26891Public exploit

Privilege escalation via overprivileged ContainerUser token

Published Mar 11, 2021 · Updated Aug 19, 2026

Privilege escalation in Microsoft Windows Container Execution Agent allows local ContainerUser processes to gain administrator access. CExecSvc creates the ContainerUser token with SeImpersonatePrivilege, which permits impersonation of an administrator or SYSTEM token. Code must already run as ContainerUser in a Windows Server Container; successful exploitation grants administrator-equivalent privileges within that container.

CVSS severity7.8

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-2021-26891
Published: Mar 11, 2021
Updated: Aug 19, 2026

Vendor: Microsoft
Product: Windows Server 2019
Classifications: T1068

Attack vector: local
Privileges: authenticated

Timeline

How it unfolded

Mar 11, 2021CVE publishedPublication date reported by the CVE source.
Aug 19, 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=10.0.17763.0 <10.0.17763.1817

What conditions does exploitation require?

Attack vectorlocal

Required privilegesauthenticated

What is affected?

Microsoft · Windows Server 2019version=10.0.17763.0 <10.0.17763.1817

Microsoft · Windows 10 Version 1909version=10.0.0 <10.0.18363.1440

Microsoft · Windows Server 2016 (Server Core installation)version=10.0.14393.0 <10.0.14393.4283

Microsoft · Windows Server, version 2004version=10.0.0 <10.0.19043.867

Microsoft · Windows Server 2016version=10.0.14393.0 <10.0.14393.4283

Microsoft · Windows 10 Version 20H2version=10.0.0 <10.0.19043.867

Microsoft · Windows Server 2019 (Server Core installation)version=10.0.17763.0 <10.0.17763.1817

Microsoft · Windows Server version 20H2version=10.0.0 <10.0.19043.867

Microsoft · Windows 10 Version 1607version=10.0.14393.0 <10.0.14393.4283

Microsoft · Windows 10 Version 2004version=10.0.0 <10.0.19043.867

Microsoft · Windows 10 Version 1809version=10.0.0 <10.0.17763.1817; version=10.0.17763.0 <10.0.17763.1817

Microsoft · Windows Server, version 1909 (Server Core installation)version=10.0.0 <10.0.18363.1440

Published CVSS scores

7.8MicrosoftCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

4.6NIST NVDAV:L/AC:L/Au:N/C:P/I:P/A:P

7.8NIST NVDCVSS: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 exploitationUnconfirmed

Public exploitPublished

Weakness, pattern, technique

T1068Exploitation for Privilege Escalation

Public exploit references

ContainerUser privilege demonstrationproof of concept · demonstrated

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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