RBAC vs ReBAC in SaaS: why access control is getting harder

At a glance

What this is: This compares RBAC and ReBAC as access-control models and shows that RBAC fits stable role structures while ReBAC fits relationship-heavy environments.

Why it matters: IAM teams need this distinction because entitlement model fit affects provisioning, review effort, auditability, and how well access scales across human, NHI, and workflow-driven programmes.

By the numbers:

• Only 5.7% of organisations have full visibility into their service accounts.
• 97% of NHIs carry excessive privileges, increasing unauthorised access and broadening the attack surface.
• 80% of identity breaches involved compromised non-human identities such as service accounts and API keys.

👉 Read Zluri's comparison of RBAC and ReBAC for access control design

Context

RBAC and ReBAC are both authorization models, but they solve different governance problems. RBAC works best when access can be expressed through stable job roles and predictable permissions, while ReBAC is designed for environments where access depends on relationships between users, objects, and organisational context. For IAM leaders, the key question is not which model sounds more modern, but which model matches the real shape of entitlement decisions across people, services, and workflows.

In practice, many organisations overextend RBAC because it is easier to understand and administer, then add exceptions when business relationships become more complex. That creates a governance gap between the policy model and how access is actually granted. This is where role explosion, manual exceptions, and weak review quality start to show up in identity lifecycle and access certification processes.

Key questions

Q: How should security teams decide between RBAC and ReBAC for SaaS access?

A: Use RBAC when access follows stable job functions and permissions change infrequently. Use ReBAC when access depends on ownership, project membership, reporting lines, or other relationships that are central to the business process. The right model is the one that matches how access is actually decided and reviewed, not the one that is easiest to describe.

Q: Why do relationship-based access models become harder to govern at scale?

A: They depend on accurate relationship data, clear ownership, and consistent logging. As the number of objects, projects, and exceptions grows, it becomes harder to prove why each entitlement exists. That makes review and offboarding more complex than in a pure role model, especially if relationship sources are inconsistent across systems.

Q: What breaks when organisations keep adding exceptions to RBAC?

A: The role catalogue grows until roles no longer represent stable business functions. At that point, auditors and reviewers cannot tell whether a role is a clean entitlement group or just a storage place for exceptions. The result is role explosion, weaker certification quality, and more manual maintenance.

Q: What should IAM teams verify before adopting a hybrid access model?

A: They should verify which access paths are role-based, which are relationship-based, and who owns each policy. They also need a revocation model that handles both paths during offboarding. Without that boundary, the hybrid design becomes difficult to certify and easy to misconfigure.

Technical breakdown

RBAC as a stable entitlement model

RBAC groups permissions into roles such as admin, editor, or viewer, then assigns those roles to users. Its strength is operational simplicity: when job functions are stable, the role map stays readable, reviews are easier, and audits can follow a clear chain from role to permission. Its weakness appears when the organisation needs many exceptions, because each exception weakens the original role logic and increases maintenance cost. RBAC is therefore a governance model as much as a technical one. Practical implication: use RBAC where access patterns are stable enough that role definitions will not churn every time the business changes.

Practical implication: reserve RBAC for access patterns that stay stable long enough to be reviewed and certified cleanly.

ReBAC and relationship-driven authorisation

ReBAC determines access from relationships such as ownership, membership, reporting lines, project participation, or resource hierarchy. That makes it better suited to collaborative systems, shared workspaces, and multi-tenant SaaS where access cannot be reduced to a small set of roles. The trade-off is that the policy logic becomes more contextual and harder to explain unless the organisation logs the relationship inputs clearly. ReBAC does not remove governance work. It shifts it from role design to relationship definition, audit traceability, and lifecycle accuracy. Practical implication: use ReBAC only where relationship context is genuinely part of the access decision and can be governed continuously.

Practical implication: define and log relationship inputs with the same discipline you apply to entitlements and approvals.

Why hybrid access models often become the real design choice

Most real systems end up using a hybrid of RBAC and ReBAC because neither model alone handles every entitlement case. RBAC covers the baseline, while ReBAC handles exceptions, collaboration, and resource-specific access. The governance risk is that hybridisation can blur ownership if teams do not decide which model is authoritative for which access path. Once that happens, reviewers see a confusing mixture of role grants and relationship grants, and access recertification loses precision. Practical implication: explicitly separate baseline role access from relationship-based exceptions so reviews, reporting, and offboarding stay coherent.

Practical implication: document which access paths are role-based, which are relationship-based, and who owns each one.

NHI Mgmt Group analysis

RBAC remains the right baseline only when entitlement logic is genuinely stable. The model works because it reduces access decisions to repeatable role-to-permission mappings, which makes audit trails and certification easier to reason about. But that strength becomes a weakness when organisations keep adding exceptions to cover collaboration, hierarchy, or tenant-specific cases. At that point, RBAC stops being a clean control model and becomes a container for policy drift. Practitioners should treat role stability as the deciding criterion, not familiarity.

ReBAC is not a better RBAC, it is a different governance problem. Relationship-based access control shifts the unit of governance from the user role to the user-object relationship, which matters in project work, shared documents, and complex SaaS. That makes it more expressive, but also more dependent on accurate metadata, lifecycle state, and logging discipline. If the organisation cannot explain or verify relationships consistently, the model will be harder to govern than RBAC. Practitioners should choose ReBAC only when the relationship itself is part of the security requirement.

Hybrid entitlement models are now the default, which makes access governance more operationally demanding. Few organisations can keep every access path inside a pure role model, so RBAC and ReBAC often coexist. The governance challenge is not coexistence itself, but unclear ownership of which model governs which decision. When that boundary is vague, access reviews become inconsistent and offboarding misses relationship-based grants. Practitioners should separate baseline entitlements, contextual exceptions, and review ownership before scale makes the model unmanageable.

Access governance for human users and NHIs breaks in the same place when entitlement logic is too coarse. Human roles, service accounts, and workflow identities all need different decision shapes, but the underlying governance lesson is the same: the access model must match the subject and the context. Excessive generalisation creates stale access, while over-specific policies create review fatigue. Practitioners should align the authorisation model to the identity type and the lifecycle process that governs it.

Relationship-based controls become a named governance gap when organisations cannot prove why access exists. Access provenance gap: RBAC can tell you what role granted access, while ReBAC can depend on relationships that are harder to certify after the fact. That means the real control question is whether the organisation can reconstruct the reason for access at review time. Practitioners should treat provenance as a first-class entitlement requirement, not a reporting afterthought.

From our research:

• 97% of NHIs carry excessive privileges, increasing unauthorised access and broadening the attack surface, according to Ultimate Guide to NHIs.
• Only 20% have formal processes for offboarding and revoking API keys, and even fewer have procedures for rotating them.
• For the lifecycle angle, review NHI Lifecycle Management Guide for provisioning, rotation, and offboarding patterns that keep entitlement models auditable.

What this signals

Access model choice is becoming an operating model decision, not just a design preference. Teams that still treat RBAC as the default and ReBAC as a niche exception will keep paying for that shortcut in role sprawl, manual approvals, and weak review quality. The governance signal is clear: entitlement design must be mapped to identity type, business process, and audit expectation before the access catalogue becomes unmanageable.

Access provenance gap: when relationship-based entitlements cannot be explained cleanly at review time, the control has already weakened. That is where identity lifecycle and IGA programmes need to be more explicit about ownership, source data, and revocation triggers. For teams formalising this work, the Ultimate Guide to NHIs remains the clearest reference point for lifecycle-linked governance.

For practitioners

• Map entitlement patterns before choosing a model Separate stable job-based access, collaboration-based access, and exception-based access. Use RBAC for the first category, ReBAC for the second, and document every exception path so reviewers can see why each entitlement exists.
• Define ownership for every relationship-driven grant Assign a business owner and an IAM owner to each ReBAC policy input such as project membership, reporting line, or object ownership. Without named ownership, relationship-based entitlements become difficult to certify or revoke.
• Limit role growth by moving exceptions out of RBAC Stop adding one-off roles for temporary collaboration or tenant-specific access. Move those cases into a controlled relationship-based policy layer so the role catalogue stays small and reviewable.
• Test offboarding against both role and relationship paths Validate that termination, project exit, and tenant removal all remove access through every path the identity can use. Relationship-based grants often survive when only the role assignment is revoked.

Key takeaways

• RBAC is strongest where permissions map cleanly to stable roles, but it weakens as exceptions accumulate.
• ReBAC improves precision in relationship-heavy environments, yet it raises the bar for logging, ownership, and auditability.
• Most organisations will need a hybrid approach, but the boundary between role-based and relationship-based access must be explicit.

Key terms

• Role-Based Access Control: A permission model that assigns access through predefined roles such as admin, editor, or viewer. It works best when job functions are stable and access patterns are repeatable. In governance terms, it is easy to review, but it can become bloated if teams keep encoding exceptions into new roles.
• Relationship-Based Access Control: A permission model that grants access based on relationships between identities, objects, and organisational context. Common relationship inputs include ownership, membership, reporting lines, and project participation. It is more expressive than role-based access, but it demands better data quality and clearer audit evidence.
• Access Provenance: The reason an identity has access and the chain of logic that explains it. Provenance can come from a role, a relationship, or both, and it matters because review teams need to know whether an entitlement still matches the business need. Without provenance, certification quality drops quickly.
• Hybrid Entitlement Model: An access-control design that uses more than one authorisation approach, usually combining roles for baseline access and relationships for exceptions or collaboration. Hybrid models are common because real organisations rarely fit one clean pattern. They work only when ownership and review boundaries are explicit.

Deepen your knowledge

NHI governance, agentic AI identity, and machine identity security are core topics in our NHI Foundation Level course, the industry's only accredited NHI security programme. If you are responsible for identity security strategy or programme maturity, it is worth exploring.

This post draws on content published by Zluri: Security & Compliance RBAC vs. ReBAC: Which Model is Right For You? Read the original.