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GeezerVison is showing github.com — Protect the fallback temporary home directory by enforcing and checking its file mode on Unix platforms by daxian-dbw · Pull Request #27985 · PowerShell/PowerShell

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@daxian-dbw

@daxian-dbw Dongbo Wang (daxian-dbw) commented Sep 8, 2026 •
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PR Summary

Protect the home fallback directory by checking its Unix permission mode -- PowerShell always creates the temporary home directory with the user-only permission, so if its mode is not what we expect, then it indicates the directory may be tampered (e.g. a different local user created it) and we fail the startup for security reason.

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Copilot AI lite review requested due to automatic review settings September 8, 2026 17:33
@daxian-dbw
Dongbo Wang (daxian-dbw) requested a review from a team as a code owner September 8, 2026 17:33
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Copilot started reviewing on behalf of Dongbo Wang (daxian-dbw) September 8, 2026 17:33
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Copilot AI reviewed Sep 8, 2026
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🟡 Changes recommended

A newly introduced user-facing error message is potentially misleading about the condition being detected, and should be adjusted for accuracy before merge.

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Pull request overview

This PR hardens PowerShell startup on Unix when HOME is not set by creating (and validating) a fallback temporary home directory with user-only permissions, and failing fast if that directory appears unsafe.

Changes:

  • Create the fallback temp HOME directory with explicit user-only Unix permissions (0700) and validate the resulting mode.
  • Add a localized error message for the unsafe-permission startup failure case.
File summaries
File Description
src/System.Management.Automation/CoreCLR/CorePsPlatform.cs Creates temp HOME with explicit UnixFileMode and throws on unexpected permissions.
src/System.Management.Automation/resources/CoreClrStubResources.resx Adds a new resource string for the unsafe temp HOME permission startup error.
Review details
  • Files reviewed: 2/2 changed files
  • Comments generated: 2
  • Review effort level: Lite

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Comment thread src/System.Management.Automation/CoreCLR/CorePsPlatform.cs Resolved

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Comment thread src/System.Management.Automation/resources/CoreClrStubResources.resx Resolved

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daxian-dbw
Dongbo Wang (daxian-dbw) commented Sep 8, 2026
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Comment thread src/System.Management.Automation/CoreCLR/CorePsPlatform.cs Resolved

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@daxian-dbw Dongbo Wang (daxian-dbw) added the CL-General Indicates that a PR should be marked as a general cmdlet change in the Change Log label Sep 8, 2026
iSazonov
Ilya (iSazonov) approved these changes Sep 9, 2026
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@daxian-dbw
Guard the home fallback directory
5a4e640
@daxian-dbw
Dongbo Wang (daxian-dbw) force-pushed the msrc-home-fallback branch from 70b55d6 to 5a4e640 Compare September 9, 2026 16:18
@daxian-dbw

Dongbo Wang (daxian-dbw) commented Sep 9, 2026

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Rebased and force-pushed the branch to fix CIs.
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@daxian-dbw Dongbo Wang (daxian-dbw) changed the title Prevent the fallback temporary home directory from being tampered Protect the fallback temporary home directory by enforcing and checking its file mode on Unix platforms Sep 16, 2026
SeeminglyScience
Patrick Meinecke (SeeminglyScience) approved these changes Sep 22, 2026
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Dongbo Wang (daxian-dbw) merged commit 154bbe8 into PowerShell:master Sep 22, 2026
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@daxian-dbw
Dongbo Wang (daxian-dbw) deleted the msrc-home-fallback branch September 22, 2026 19:36
@daxian-dbw Dongbo Wang (daxian-dbw) added the Backport-7.7.x-Consider label Sep 22, 2026
@daxian-dbw Dongbo Wang (daxian-dbw) added Backport-7.7.x-Done and removed Backport-7.7.x-Consider labels Oct 27, 2026
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@iSazonov Ilya (iSazonov) iSazonov approved these changes
@SeeminglyScience Patrick Meinecke (SeeminglyScience) SeeminglyScience approved these changes

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@daxian-dbw @iSazonov @SeeminglyScience
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