They often review permissions identity by identity and miss the combined access graph. In merged estates, the real risk is transitive reach, where two separately acceptable identities create a toxic combination that unlocks data, admin paths, or build systems neither side intended to expose.
Why This Matters for Security Teams
least privilege gets misread in merged environments because teams often think in terms of isolated accounts instead of combined reach. After an acquisition, migration, or platform consolidation, permissions that looked acceptable in one estate can become dangerous when linked to shared admin groups, federated trust, or duplicated service accounts. NHI Mgmt Group notes that 97% of NHIs carry excessive privileges, which makes hidden overlap more likely than teams expect, especially when visibility is fragmented across directories and cloud tenants.
The practical problem is not just access sprawl. It is the way separately approved identities can form a toxic path once they are connected through trust relationships, build pipelines, or cross-domain automation. That is why least privilege has to be evaluated against the access graph, not the ticket history. The Ultimate Guide to NHIs frames this as a visibility and governance failure, while the OWASP Non-Human Identity Top 10 highlights how over-privileged service identities become attack paths once compromise or misconfiguration occurs.
In practice, many security teams discover the problem only after a migration has already created new lateral paths, rather than through intentional access review.
How It Works in Practice
Effective least privilege in merged estates starts with treating identity as a graph problem. That means mapping humans, service accounts, workload identities, API keys, CI/CD tokens, and delegated admin paths together, then asking what each identity can reach when combined with others. A single account may look low risk on paper, but if it can invoke a pipeline, write to a secrets store, or assume a cloud role, it may complete a privilege chain that neither source estate had before.
Current guidance suggests three operational moves. First, inventory inherited identities and normalize them into one control plane. Second, identify transitive trust paths, especially where group nesting, role assumption, federation, or shared automation exists. Third, reissue access using least-privilege roles that are scoped to the merged operating model rather than preserving legacy entitlements. This is where NHIMG research on key challenges and risks is especially useful, because it emphasizes that incomplete visibility and unmanaged lifecycle practices often hide the true exposure.
- Review entitlement chains, not just direct permissions.
- Separate standing admin rights from task-based access.
- Revalidate trust between directories, tenants, and SaaS platforms after every merger event.
- Prefer short-lived, scoped credentials for automation where possible.
The NIST SP 800-207 Zero Trust Architecture aligns with this approach because it requires continuous verification and explicit authorization instead of assuming inherited trust is safe. These controls tend to break down when legacy directories, hardcoded secrets, and unmanaged service accounts remain active across multiple cloud tenants because the combined trust graph becomes too large to validate manually.
Common Variations and Edge Cases
Tighter least-privilege enforcement often increases operational overhead, so organisations have to balance reduced exposure against migration speed, uptime, and support complexity. That tradeoff becomes sharper in merged environments because business units may insist on preserving legacy access until integration is complete. Best practice is evolving, but there is no universal standard for this yet: some teams start with read-only access freezes, while others use risk-ranked remediation based on the most privileged paths first.
One common edge case is identity duplication, where both estates have service accounts that appear unrelated but actually point to the same backend resource. Another is “shadow delegation,” where a seemingly harmless group grants indirect rights through nested roles or cross-account assumption. A third is operational tooling that breaks if permissions are trimmed too quickly, especially in CI/CD and infrastructure automation. The OWASP Non-Human Identity Top 10 is useful here because it reinforces that over-privileged machine identities are rarely obvious until the estate is normalized.
Teams usually get the best results by pairing access reduction with strong exception handling, time-bounded approvals, and periodic graph review. That is especially true when third-party integrations, federated identity, or M&A carve-outs preserve temporary trust longer than intended.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
OWASP Non-Human Identity Top 10 address the attack and risk surface, while NIST CSF 2.0 and NIST AI RMF set the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| OWASP Non-Human Identity Top 10 | NHI-03 | Over-privileged machine identities often form hidden access chains in merged estates. |
| NIST CSF 2.0 | PR.AA-01 | Least privilege in merged environments depends on knowing and governing effective identities. |
| NIST AI RMF | GOVERN | Merged environments need accountability for access decisions across combined identity graphs. |
Map and trim each NHI’s effective reach after trust relationships and group nesting are normalized.
Related resources from NHI Mgmt Group
Deepen Your Knowledge
Reviewed and updated by the NHIMG editorial team on July 6, 2026.
NHI Mgmt Group — the #1 independent authority on Non-Human Identity, IAM, and Agentic AI security. nhimg.org
