Orphaned SIDs and Deleted Accounts

When user accounts are deleted from Active Directory or local Windows systems, their permissions on files and folders don't automatically disappear. Instead, these permissions remain in place but display as cryptic Security Identifiers (SIDs) rather than readable account names - these are commonly called "orphaned SIDs" or "unresolved SIDs."

You've likely seen them: permission entries that look like S-1-5-21-3623811015-3361044348-30300820-1013 instead of DOMAIN\jsmith. These orphaned permissions represent a security and compliance concern that many organizations overlook.

This guide explains what orphaned SIDs are, why they matter, and how to efficiently locate them across your file system using Permissions Reporter's built-in filtering capabilities.

What Are Orphaned SIDs?

Understanding Security Identifiers

Every security principal in Windows - whether a user account, group, or computer - is assigned a unique Security Identifier (SID). When you grant permissions to DOMAIN\jsmith, Windows actually stores that permission using John's SID, not his username. The friendly name you see is simply a translation that Windows performs by looking up the SID in Active Directory or the local SAM database.

When SIDs Become Orphaned

A SID becomes "orphaned" when the account it represents no longer exists:

• User account deletion - An employee leaves and their AD account is removed
• Group deletion - A security group is deleted but was still referenced in ACLs
• Domain trust removal - A trusted domain relationship is severed
• Domain migration issues - Accounts weren't properly migrated between domains
• Computer account removal - Machine accounts deleted from AD

When Windows can't resolve a SID to a name, it displays the raw SID string instead. This is your visual indicator that something has been deleted or is otherwise unreachable.

The Security Implications

Orphaned SIDs pose several risks:

• SID reuse vulnerability - In rare cases, a new account could be assigned the same SID as a deleted account, inadvertently inheriting its permissions
• Audit confusion - Security audits become difficult when you can't determine who had access
• Compliance violations - Regulations like SOX, HIPAA, and PCI-DSS require knowing who has access to sensitive data
• Accumulation over time - Without regular cleanup, ACLs become cluttered and harder to manage
• Potential attack surface - Orphaned SIDs from compromised accounts may still grant unintended access

Common Causes of Orphaned SIDs

Employee Offboarding

The most common source of orphaned SIDs is employee turnover. When IT deletes a user's Active Directory account, any explicit permissions that user had on files and folders remain in place. Organizations with high turnover or poor offboarding processes accumulate orphaned SIDs rapidly.

Group Policy and Security Group Changes

Security groups are frequently reorganized, renamed, or deleted as organizational structures change. Deleted groups leave orphaned SIDs on any resources where they had explicit permissions.

Domain Migrations and Consolidations

Mergers, acquisitions, and domain consolidations often result in orphaned SIDs when:

• Source domain accounts aren't migrated with SID history
• Trust relationships are removed before permission cleanup
• Migration tools don't properly translate permissions

Related: For environments that have undergone domain migrations, see our guide on SID History and NTFS Permissions to understand how historical SIDs interact with current access.

Finding Orphaned SIDs Manually

The Traditional Approach

Without specialized tools, finding orphaned SIDs requires:

1. Navigating to each folder in Windows Explorer
2. Opening the Security tab in Properties
3. Visually scanning for SID strings instead of account names
4. Documenting findings manually
5. Repeating for every folder in your environment

Limitations of Manual Methods

This approach has significant drawbacks:

• Time-consuming - Large file systems with thousands of folders make manual review impractical
• Error-prone - Easy to miss orphaned SIDs, especially in complex ACLs
• No historical tracking - No way to compare findings over time
• Incomplete coverage - Subfolders with unique permissions are easily overlooked
• No reporting - Difficult to provide audit evidence to compliance teams

Using Permissions Reporter to Find Orphaned SIDs

Permissions Reporter includes a built-in filter preset specifically designed to locate permissions referencing deleted or unknown accounts. Here's how to use it:

Step 1: Create or Open a Project

1. Launch Permissions Reporter
2. Create a new project or open an existing one
3. Add the folder paths you want to analyze
4. Run the initial permissions scan

Step 2: Apply the Orphaned SIDs Filter Preset

1. After the scan completes, click the Filter dropdown in the main toolbar
2. Select Edit Post-Scan Filter to open the filter editor
3. In the filter editor toolbar, click the Quick button
4. Select "Permissions referencing deleted or unknown accounts" from the quick filter menu
5. Click Apply to filter the results

Understanding the filter: The preset configures a filter rule that checks the "SID resolution failed" criteria. This identifies any permission entry where Windows was unable to translate the stored SID into an account name - the definitive indicator of an orphaned SID.

Step 3: Review the Results

The filtered view now shows only folders and files containing orphaned SID permissions. For each result, you can see:

• The full SID string (e.g., S-1-5-21-...)
• The permission type (Allow/Deny)
• The access rights granted
• The inheritance status
• The folder path

Step 4: Export for Documentation

For compliance documentation or remediation planning:

1. Click Export in the toolbar
2. Choose your format (Excel, CSV, HTML, or XML)
3. The export includes all filtered results with full details

Best practice: For large environments, scan incrementally by focusing on sensitive data locations first. Use the built-in scheduler to set up recurring reports and catch new orphaned SIDs as they appear.

Remediation: Removing Orphaned SIDs

Once you've identified orphaned SIDs, you have several remediation options:

Option 1: Manual Removal via Windows Explorer

For small numbers of orphaned SIDs:

1. Navigate to the identified folder
2. Right-click and select Properties
3. Go to the Security tab
4. Click Edit
5. Select the orphaned SID entry
6. Click Remove
7. Click Apply and OK

Option 2: PowerShell Bulk Removal

For larger cleanup efforts, PowerShell can remove orphaned SIDs programmatically:

# Example: Remove orphaned SIDs from a folder
$acl = Get-Acl "C:\Data\SharedFolder"
$orphanedRules = $acl.Access | Where-Object {
    $_.IdentityReference.Value -match '^S-1-5-21-'
}
foreach ($rule in $orphanedRules) {
    $acl.RemoveAccessRule($rule)
}
Set-Acl "C:\Data\SharedFolder" $acl

Caution: Always test scripts in a non-production environment first and ensure you have backups. Export a Permissions Reporter report before making bulk changes so you can verify what was removed.

Best Practices for Remediation

• Document before removing - Export a report of orphaned SIDs before cleanup
• Test in limited scope - Start with a small folder set to verify your process
• Verify inheritance - Ensure cleanup doesn't break intended inheritance patterns
• Update your offboarding process - Address the root cause, not just symptoms
• Schedule regular audits - Make orphaned SID detection part of routine maintenance

Preventing Future Orphaned SIDs

Improve Offboarding Procedures

The best defense against orphaned SIDs is a robust offboarding process:

1. Audit permissions before deletion - Run a Permissions Reporter scan filtered to the departing user before removing their account
2. Reassign ownership - Transfer file ownership to managers or successors
3. Remove explicit permissions - Clean up direct permission grants
4. Document the cleanup - Maintain records for compliance

Use Groups Instead of Direct Permissions

Following the AGDLP (or AGUDLP) model reduces orphaned SID accumulation:

• Assign permissions to Domain Local groups only
• Add users to Global groups that are members of Domain Local groups
• When users leave, simply remove them from groups - no file system cleanup needed

Best practice: When users are granted access through groups rather than direct permissions, deleting their account leaves no orphaned SIDs behind. This is the single most effective way to prevent orphaned SID accumulation.

Implement Regular Audits

Schedule quarterly or monthly permission scans to catch orphaned SIDs early:

• Use Permissions Reporter's built-in scheduler
• Configure email notifications for report delivery
• Use the report comparison feature to track trends over time

Related Resources

• Advanced Filtering in Permissions Reporter - Learn more about filtering capabilities
• NTFS Permissions Overview - Understand how Windows permissions work
• Auditing NTFS Permissions - Comprehensive audit guide
• SID History and NTFS Permissions - Understanding migrated account permissions