What breaks when access groups are duplicated instead of organised into a hierarchy?

Why This Matters for Security Teams

Duplicated access groups are not just an administrative nuisance. They weaken the identity model by making it unclear which group is authoritative, which permissions are inherited, and which exceptions are intentional. That creates review fatigue, hidden privilege drift, and inconsistent enforcement across teams. For non-human identities, the impact is sharper because service accounts, API keys, and automation often depend on repeatable access paths that should be easy to audit. NHI Management Group notes that 97% of NHIs carry excessive privileges, which makes over-provisioning a persistent risk when group design is messy, as discussed in the Ultimate Guide to NHIs. OWASP’s Non-Human Identity Top 10 also frames identity sprawl and weak lifecycle control as recurring failure modes. In practice, many security teams encounter duplicated group risk only after an access review, incident, or cleanup effort has already exposed years of inconsistent entitlement growth.

How It Works in Practice

A hierarchy gives access groups a parent-child structure so that common permissions are defined once and inherited, while narrower access is layered only where needed. That reduces duplication and makes it easier to answer practical questions such as: what does every application in this domain receive by default, and what additional access is unique to this workload? For NHI governance, that matters because machine identities should be managed as workloads with predictable permission boundaries rather than as one-off exceptions. Effective implementations usually combine group hierarchy with role definitions, ownership, and periodic review. Security teams should separate:

• baseline access for a function or environment
• exception access for a specific application, pipeline, or service account
• temporary access that should expire through just-in-time approval
• service-specific entitlements that should not be inherited broadly

This model aligns well with the control expectations in NIST SP 800-53 Rev. 5, especially where least privilege, account management, and separation of duties are required. It also supports NHI lifecycle practices described in the Ultimate Guide to NHIs, particularly where visibility and rotation depend on knowing which identities inherit what. A hierarchy also makes access reviews more meaningful because reviewers can validate the parent group once and then inspect only the exceptions below it. These controls tend to break down in flat directory environments where application teams create near-duplicate groups independently and no one owns the inheritance model.

Common Variations and Edge Cases

Tighter hierarchy usually increases design and governance overhead, requiring organisations to balance clean inheritance against the risk of over-broad parent groups. That tradeoff matters when different business units need similar but not identical access, or when legacy systems cannot interpret nested groups consistently. Current guidance suggests avoiding deep nesting unless the directory platform, review process, and ownership model are mature enough to support it. There is no universal standard for how many levels of hierarchy are optimal. In practice, the better test is whether a reviewer can explain the access path without tracing a maze of duplicates. Flat structures may still be acceptable for small teams with stable systems, but they become fragile when multiple platforms, environments, or NHI classes share the same directory. This is where duplicated groups create the most damage: the permissions look equivalent until an incident, audit, or offboarding event reveals they were never truly aligned. For larger environments, the best practice is evolving toward hierarchy plus explicit exception handling, rather than unlimited duplication. That is especially important for machine identities, where a single service account may accumulate access through several groups and the real effective privilege becomes hard to reconstruct. A useful reference point is the 52 NHI Breaches Analysis, which shows how identity confusion and excessive access often reinforce each other.

Related resources from NHI Mgmt Group

• What breaks when organisations try to review access manually across nested groups and foreign security principals?
• What breaks when access requests are treated as broad group membership instead of specific resource and role decisions?
• How should security teams govern access reviews in complex Active Directory environments with nested groups and multiple domains?
• What breaks when database access is granted with static users and preconfigured broad roles?