Supabase vs Firebase: Security Model Comparison

Supabase vs Firebase: How Their Security Models Compare

Supabase and Firebase are the two dominant backend-as-a-service platforms, and both take security seriously. However, they implement authorization and data protection through fundamentally different mechanisms. Understanding these differences is essential for architects choosing between platforms and for security engineers auditing applications built on either.

The Core Difference: SQL vs Custom DSL

Supabase's security model is built on PostgreSQL's Row-Level Security (RLS). Security policies are written in SQL, the same language used for queries. This means that any developer who knows SQL can read and write security policies, and the policies operate at the database engine level, ensuring they cannot be bypassed by application code (unless the service role key is used).

Firebase uses a custom domain-specific language for its security rules. Firestore, Realtime Database, and Cloud Storage each have their own rule syntax, though they share common patterns. These rules are evaluated by Firebase's infrastructure before any read or write operation is executed.

Both approaches are effective, but they have different ergonomic and security implications.

Granularity and Flexibility

Supabase RLS operates at the row level within SQL tables and can be extended to column-level restrictions using views or column grants. Because policies are SQL expressions, they can reference other tables, use subqueries, and leverage the full power of PostgreSQL's type system and functions. This makes it possible to express complex authorization logic, such as "users can only read rows where their organization_id matches and they have the 'viewer' role in the organization_members table."

Firebase Security Rules operate at the document level for Firestore and at the node level for Realtime Database. Rules can reference the authenticated user's token claims, the document being accessed, and other documents in the database (through get() and exists() functions). However, the rule language is less expressive than SQL for complex authorization logic, and cross-document references can impact performance.

Default Security Posture

When you create a new table in Supabase, it has no RLS policies by default. If RLS is enabled on the table (which is recommended), this means no one can access the data through the API, not even authenticated users. You must explicitly create policies to grant access. This "deny by default" approach is secure but can confuse developers who expect their queries to work immediately after creating a table.

Firebase offers two starting modes: locked mode (which denies all reads and writes) and test mode (which allows all reads and writes for a limited time). Test mode is convenient for prototyping but is a notorious source of security vulnerabilities when developers forget to replace the permissive rules before going to production. Google has added warnings and time limits to mitigate this, but open Firebase databases remain one of the most common BaaS security issues.

API Key Model

Both platforms expose public API keys that are intended to be used in client-side code. Supabase's anon key and Firebase's API key are not secrets. They are designed to be public, with security enforced by RLS policies (Supabase) or security rules (Firebase). However, this is a common source of confusion, and many developers mistakenly treat these keys as secrets or, worse, expose their service role key (Supabase) or Admin SDK credentials (Firebase) in client code.

The service role key in Supabase bypasses all RLS policies, making it extremely powerful and dangerous if exposed. Firebase's Admin SDK similarly bypasses all security rules. Both should only be used in secure server-side environments.

Testing and Validation

Firebase has a clear advantage in security rule testing tooling. The Firebase Emulator Suite allows developers to write unit tests for their security rules using the @firebase/rules-unit-testing library. This enables test-driven development of security rules, where rules are verified against specific scenarios before deployment.

Supabase security testing is typically done through SQL queries run against the database with different roles. While this works, it is less structured than Firebase's testing framework. Tools like AuditYourApp help bridge this gap by providing automated testing of RLS policies across all tables and authentication contexts.

Real-Time Security

Both platforms apply their security models to real-time data subscriptions. In Supabase, RLS policies filter which rows a client receives through real-time channels. In Firebase, security rules determine which documents or nodes a client can listen to. However, the implementation details differ.

Supabase's real-time system filters data at the database level, meaning clients only receive rows they are authorized to see. Firebase evaluates rules when a listener is attached and can reject the listener entirely if the rules do not permit the requested access pattern.

Common Vulnerabilities

Both platforms share common vulnerability patterns: overly permissive rules, missing authentication checks, exposed admin credentials, and insecure direct object references. However, each platform also has unique vulnerability patterns.

Supabase-specific risks include missing RLS on new tables, policies that only cover SELECT but not INSERT/UPDATE/DELETE, and functions that run with SECURITY DEFINER privilege unnecessarily.

Firebase-specific risks include test-mode rules left in production, wildcard rules that match more documents than intended, and rules that rely on client-provided data for authorization decisions.

Which Is More Secure?

Neither platform is inherently more secure than the other. Both provide robust security mechanisms that, when properly configured, effectively protect user data. The security of your application depends far more on how correctly you implement and maintain your security policies than on which platform you choose.

For teams choosing between the two, consider your existing expertise (SQL vs Firebase rules), your application's authorization complexity, and which ecosystem better fits your overall architecture. For security auditing on either platform, AuditYourApp provides comprehensive scanning that understands both security models.