TLDR: check out this over-engineered project and let me know what you think.
Orphaned SIDs (Security Identifiers) occur when user or group accounts are deleted from Active Directory, but their SIDs remain referenced in access control lists (ACLs) on files, folders, registry keys, or other AD objects. These leftover references appear as unresolved SIDs that Windows can no longer translate back to readable account names.
How Orphaned SIDs Accumulate
When you delete a user or group from AD, Windows doesn't automatically scan every resource to remove that SID from permissions. The deletion only removes the account object itself, leaving behind a trail of security references throughout your environment. This commonly happens during employee departures, organizational restructuring, or domain migrations where accounts are removed but their permissions persist.
Why Cleanup is Essential
Orphaned SIDs create several problems. They clutter security reports and access reviews, making it difficult to audit who actually has access to resources. They can cause performance issues as Windows attempts to resolve these dead references during permission checks. From a security perspective, they represent unclear access rights that could potentially be exploited if those SIDs were ever recreated or if there are bugs in how Windows handles unresolved identities.
Most importantly, they violate the principle of least privilege by maintaining phantom permissions that no legitimate user can exercise, creating confusion about your actual security posture.
The Cleanup Process
A typical cleanup script would scan ACLs across your environment, identify SIDs that can't be resolved to current AD objects, verify they're truly orphaned (not from trusted domains or built-in accounts), and then remove those entries from the permission sets. This process requires careful validation to avoid accidentally removing legitimate cross-domain references or system accounts.
Regular cleanup of orphaned SIDs helps maintain a clean, auditable security environment and ensures your access controls accurately reflect your current organizational structure.
Find-UnknownSID: An Over-Engineered Solution
With this background in mind, let me share the solution I developed. I had a simple task: find and remove orphaned SIDs in Active Directory. I did that and it was functional as a one-off script. But what about turning it into proper automation, with comprehensive logging, batching capabilities, memory limits, and a way to recover when things go wrong? What about Pester tests for each function so we can host this in CI/CD pipelines and ensure reliability?
Well, you're in luck because I have completely over-engineered exactly that.
Please visit this blog's companion GitHub repository to find the full solution. I won't spend much time in this post going into the implementation details since I've provided thorough documentation within the project itself. I built this solution within the constraints of my working environment: leveraging Active Directory, PowerShell 5.1, and Pester 3.4 – all products of yesteryear, but still widely deployed in enterprise environments.
Key features of the solution include:
- Comprehensive logging and error handling
- Batch processing to manage memory usage
- Recovery mechanisms for restoration of objects
- Full Pester test coverage for CI/CD integration (over 2700 tests)
- Detailed documentation and usage examples
Important Note: As with any script that modifies security permissions, always test thoroughly in a non-production environment first and ensure you have proper backups and rollback procedures in place.
If you find this solution useful in your environment, please let me know! I'd love to hear about your experiences with orphaned SID cleanup and any improvements you might suggest.