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Use Original ACLs

UseOriginalACLs is a sandbox setting in Sandboxie Ini available since v1.15.0 / 5.70.0. This setting preserves the original Access Control Lists (ACLs) on files and folders when they are copied or created within the sandbox, rather than applying Sandboxie's default security descriptor. When enabled, files maintain their original security permissions while adding the current user to the ACL with full access rights.

Usage

[DefaultBox]

UseOriginalACLs=y

Technical Details

When UseOriginalACLs=y is set, Sandboxie modifies its file operation behavior in several key areas:

  1. File Creation: Instead of using the standard Secure_NormalSD security descriptor, the system duplicates the security descriptor from the original file location and adds the current user with full access rights1.

  2. Directory Creation: When creating directories, the system queries the security descriptor of the source directory and applies it to the sandbox copy while ensuring the current user has access2.

  3. File Copying: During file copy operations, both regular files and reparse points (symbolic links, junction points) preserve their original security descriptors3.

Security Implications

  • Enhanced Compatibility: Applications that rely on specific ACL configurations will function correctly within the sandbox
  • MSI Installer Support: Particularly beneficial for MSI installers that require specific ACL permissions (hence the UI note about MSIServer exemptions)
  • User Access Guarantee: The current user is always added to the ACL with GENERIC_ALL permissions, ensuring sandbox functionality is maintained4

Implementation Notes

The setting is controlled by the global variable Secure_CopyACLs which is initialized during DLL startup5. When active, the system:

  • Queries source file security descriptors using DACL_SECURITY_INFORMATION | SACL_SECURITY_INFORMATION | GROUP_SECURITY_INFORMATION.
  • Duplicates the security descriptor to self-relative format if necessary.
  • Adds an Access Control Entry (ACE) for the current user with inheritance flags CONTAINER_INHERIT_ACE | OBJECT_INHERIT_ACE | INHERITED_ACE.

  1. File creation logic in file.c: When Secure_CopyACLs is true, File_DuplicateSecurityDescriptor duplicates the original security descriptor and File_AddCurrentUserToSD adds the current user with full permissions. ↩

  2. Directory creation in file.c: The system opens the source directory with FILE_READ_ATTRIBUTES, queries its security descriptor, and applies it to the new directory after adding current user access. ↩

  3. File copy operations in file_copy.c: Both regular file copying and reparse point copying preserve original ACLs by querying the source security descriptor with NtQuerySecurityObject. ↩

  4. ACL modification in file.c: RtlAddAccessAllowedAceEx adds the current user with GENERIC_ALL permissions and inheritance flags CONTAINER_INHERIT_ACE | OBJECT_INHERIT_ACE | INHERITED_ACE. ↩

  5. Initialization in secure.c: Secure_CopyACLs = SbieApi_QueryConfBool(NULL, L"UseOriginalACLs", FALSE) sets the global variable during DLL initialization. ↩