Security: Fix Local privilege escalation via DLL hijack#46145
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Pull request overview
This PR hardens per-machine custom install locations to mitigate a local privilege escalation vector where permissive inherited ACLs allow non-admin users to plant DLLs in a directory that is added to PATH.
Changes:
- Adds a new deferred, non-impersonated MSI custom action to secure the install folder ACL for per-machine installs outside Program Files.
- Implements ACL templating based on Program Files and reapplies hardened ACLs across the existing install tree during upgrade/repair.
- Wires the new custom action into the WiX installer sequencing for per-machine scenarios.
Reviewed changes
Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.
| File | Description |
|---|---|
| installer/PowerToysSetupVNext/Product.wxs | Schedules the new SecureInstallFolderAcl custom action and its property setup for per-machine installs. |
| installer/PowerToysSetupCustomActionsVNext/pch.h | Adds ACL API header include needed for the new security logic. |
| installer/PowerToysSetupCustomActionsVNext/CustomAction.def | Exports the new custom action entrypoint for MSI to invoke. |
| installer/PowerToysSetupCustomActionsVNext/CustomAction.cpp | Implements the install-folder ACL hardening + recursive re-ACL logic. |
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
…nto dev/vanzue/fix-sec
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DHowett
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Mar 16, 2026
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why does this require hundreds of lines of custom action code? does WiX not support ACLs?
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Thanks @DHowett Would you help take a look again see if this is a correct fix? |
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Mar 17, 2026
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This looks like it could be correct. Can you add a comment to the WXS file explaining the meaning of the SDDL string?
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Done, thanks!! |
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Summary of the Pull Request
Attack vector:
The fix is to:
PR Checklist
Detailed Description of the Pull Request / Additional comments
Validation Steps Performed
After upgrade, the ACL:
Path : Microsoft.PowerShell.Core\FileSystem::C:\apps\Power Toys\DSCModules
Owner : NT AUTHORITY\SYSTEM
Group : NT AUTHORITY\SYSTEM
Access : CREATOR OWNER Allow 268435456
NT AUTHORITY\SYSTEM Allow FullControl
BUILTIN\Administrators Allow FullControl
BUILTIN\Users Allow ReadAndExecute, Synchronize
Audit :
Sddl : O:SYG:SYD:P(A;OICIIO;GA;;;CO)(A;OICI;FA;;;SY)(A;OICI;FA;;;BA)(A;OICI;0x1200a9;;;BU)