Container escape via incorrect silo root selection
Published Mar 11, 2021 · Updated Aug 19, 2026
Privilege escalation in Microsoft Windows Container Execution Agent allows local users in a process-isolated container to access the host. The object manager asks PsGetCurrentSilo for a silo root without verifying that the returned job is a server silo, so an unprivileged application silo selects the global object-manager root. Exploitation requires code running as ContainerUser in a process-isolated Windows Server container and exposes host files and ALPC ports, enabling a chained escape with full host control.
Summary
What happened
Privilege escalation in Microsoft Windows Container Execution Agent allows local users in a process-isolated container to access the host. The object manager asks PsGetCurrentSilo for a silo root without verifying that the returned job is a server silo, so an unprivileged application silo selects the global object-manager root. Exploitation requires code running as ContainerUser in a process-isolated Windows Server container and exposes host files and ALPC ports, enabling a chained escape with full host control.
The record
- CVE
- CVE-2021-26865
- Published
- Mar 11, 2021
- Updated
- Aug 19, 2026
- Vendor
- Microsoft
- Product
- Windows Server 2019
- Classifications
- CWE-269, T1611
- 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?
What is affected?
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.
Public exploit references
- Project Zero application-silo container escape demonstrationfunctional · 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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