What Is RBAC vs ABAC vs FGAC?

SamuelApril 8, 2026Last Updated: August 13, 20262 min read

Focus: RBAC vs ABAC | Risk Level: High | Stack: Supabase RLS | Detection: Ubserve Runtime Simulation

Focus: RBAC vs ABAC
Risk: High
Stack: Supabase RLS
Detection: Ubserve Runtime Simulation

RBAC vs ABAC vs FGAC is an authorization model comparison showing how access rules are enforced — the choice affects tenant isolation and BOLA/IDOR risk.

RBAC controls by role, ABAC by attributes, and FGAC by fine-grained object/field-level policy enforcement.

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RBAC assigns permissions by role, ABAC evaluates policy from attributes, and FGAC enforces permissions at detailed resource scope such as rows, fields, or actions. AI-built SaaS stacks usually need all three layers working together, not a single model used in isolation.

A role-only setup can look correct in demos while still exposing sensitive records in production. This is common in generated auth code where "admin" and "member" checks exist, but object ownership, tenant boundaries, and field-level restrictions are missing.

A simple analogy: RBAC is like giving someone a job title badge, ABAC is checking additional context like time and location, and FGAC is deciding exactly which file cabinet drawer they can open. Modern SaaS security fails when teams stop at the badge.

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Model Comparison

Model	Decides access by	Example rule	Where it fails alone
RBAC	Assigned role	"Admins can delete invoices"	Doesn't know which invoices — any admin, any tenant
ABAC	Contextual attributes	"Allow if `plan = pro` and `time < trial_end`"	Powerful but hard to audit; easy to write overly-broad conditions
FGAC (e.g. Supabase RLS)	Row/field-level ownership	"Allow if `invoice.tenant_id = auth.uid()'s tenant`"	Requires policies on every table — one missing policy reopens the gap

Why Stopping at RBAC Causes BOLA/IDOR

This comparison isn't academic — it's the direct fix for BOLA/IDOR, the most common access-control bug in AI-generated apps. RBAC answers "can this role perform this action, in general." FGAC answers "can this specific actor touch this specific row." A codebase with only the first question answered is exactly the shape broken access control takes in practice.

Agentic Risk (Cursor, v0, Bolt)

Generated auth logic often stops at RBAC checks and misses object-level constraints. Ubserve 2026 findings show 21.7% of AI-built apps had role-correct but object-insecure flows.

Wrong vs. Right

WRONG: "admin|member" role check only
RIGHT: role check + tenant attribute + object ownership/FGAC policy

Copy-Paste Fix Prompt for Cursor/Claude

Refactor my authorization model using RBAC + FGAC.
1. Keep RBAC for broad action classes.
2. Add FGAC policies for tenant/object-level reads and writes.
3. Add ABAC claims where role-only logic is insufficient.
4. Produce migration steps and regression tests.
Return policy matrix + code updates.

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About the author

Samuel

Founder & maker of Ubserve

I'm Samuel, known online as Mr. Ballaz. I build Ubserve, a security scanner for apps built with AI tools like Cursor, Bolt, Lovable, and Supabase. Before Ubserve, I did manual security audits by hand — checking auth, exposed keys, and RLS policies one by one. Ubserve is that manual audit, automated, running in under 60 seconds instead of days.

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How Ubserve Applies This in Real Scans

Ubserve treats What Is RBAC vs ABAC vs FGAC? as a production risk, not a theory term. Our runtime simulation maps this control to attacker paths in auth, data access, and API behavior, then returns fix-ready guidance tied to your stack. OWASP-style principles are used as the baseline, but we prioritize what is actually exploitable in your live flow.

Detection

Runtime exploit simulation + behavioral authorization checks.

Evidence

Clear proof path showing where trust boundaries fail.

Remediation

AI-ready fix prompts and implementation-level patch guidance.

FAQs

Which model is best for multi-tenant SaaS?+

Most production systems combine RBAC for broad permissions with FGAC/RLS for tenant and object-level enforcement. Neither one alone is sufficient for a multi-tenant app.

Does RBAC alone prevent BOLA/IDOR?+

No. RBAC answers "what can this role do in general", not "does this specific user own this specific record." A role-only check will happily let a valid "member" read another tenant's data if there's no object-level constraint underneath it. See BOLA/IDOR for the exploit this gap enables.

How does Supabase Row Level Security map to these models?+

Supabase RLS is Postgres's native implementation of FGAC — policies are evaluated per row, scoped to auth.uid() or custom claims. It's the enforcement layer that makes RBAC/ABAC decisions actually stick at the database level, not just in application code.

Do I need all three models at once?+

In practice, yes, at different layers: RBAC for coarse feature gating in the UI, ABAC where a decision depends on context like time or plan tier, and FGAC/RLS as the non-negotiable last line of defense at the data layer.

Glossary to action

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