Default Function EXECUTE to PUBLIC

What “Default Function EXECUTE to PUBLIC” means (plain English)

Default Function EXECUTE to PUBLIC means new database functions may be callable by more roles than you intended. Teams often secure tables but forget routine privileges. Attackers can invoke helper functions directly and trigger reads or side effects that bypass app-level guardrails.

How Default Function EXECUTE to PUBLIC works in Supabase/Postgres (technical)

PostgreSQL defaults can grant EXECUTE to PUBLIC for functions unless altered. In Supabase projects with exposed schemas, this can create unexpected RPC callable surface. Mitigation includes revoking EXECUTE from PUBLIC where appropriate, setting ALTER DEFAULT PRIVILEGES for routine creation roles, and routing privileged operations through backend-only endpoints.

Attack paths & failure modes for Default Function EXECUTE to PUBLIC

• Default Function EXECUTE to PUBLIC: direct API bypass: A team validates behavior only through UI flows, but an attacker calls the underlying Supabase endpoint directly with client credentials. Because default function execute to public is present, the attacker can read or trigger operations outside intended authorization boundaries.
• Default Function EXECUTE to PUBLIC: migration drift regression: The team previously hardened this area, but a later migration adds objects, privileges, or settings without full security review. The rollout reopens default function execute to public and restores an exploitable path in production.
• Default Function EXECUTE to PUBLIC: direct API bypass: Security controls depended on frontend behavior and partial configuration checks. The underlying grants, schema exposure, or policy predicates still allowed direct access patterns that untrusted clients could reproduce.
• Default Function EXECUTE to PUBLIC: migration drift regression: Migrations were treated as schema-only changes without mandatory security gates. No automated checks validated grants, exposed schema settings, or authorization behavior before deployment.
• The configuration doesn’t match what the UI implies (direct API access bypasses the app).
• Policies/grants drift over time and widen access without anyone noticing.
• Fixes are applied without verification, leading to false confidence.

Why Default Function EXECUTE to PUBLIC matters for Supabase security

Function privilege drift is easy to reintroduce through migrations. Locking down default EXECUTE prevents newly shipped routines from becoming instant attack surface and keeps RPC exposure intentional.

Common Default Function EXECUTE to PUBLIC mistakes that lead to leaks

• Revoking EXECUTE on existing routines once, but not setting default privileges for future migrations.
• Assuming function names are obscure enough to protect them from discovery or invocation.
• Exposing admin-like routines in schemas reachable by client credentials.
• Default Function EXECUTE to PUBLIC: direct API bypass: Security controls depended on frontend behavior and partial configuration checks. The underlying grants, schema exposure, or policy predicates still allowed direct access patterns that untrusted clients could reproduce.
• Default Function EXECUTE to PUBLIC: migration drift regression: Migrations were treated as schema-only changes without mandatory security gates. No automated checks validated grants, exposed schema settings, or authorization behavior before deployment.

Where to look for Default Function EXECUTE to PUBLIC in Supabase

• Your grants, policies, and any direct client access paths.
• Storage and RPC settings (common blind spots).

How to detect Default Function EXECUTE to PUBLIC issues (signals + checks)

Use this as a quick checklist to validate your current state:

• Try the same queries your frontend can run (anon/authenticated). If sensitive rows come back, you have exposure.
• Verify RLS is enabled and (for sensitive tables) forced.
• List policies and look for conditions that don’t bind rows to a user or tenant.
• Audit grants to anon / authenticated on sensitive tables and functions.
• Default Function EXECUTE to PUBLIC: direct API bypass: Frontend checks are UX, not authorization.
• Default Function EXECUTE to PUBLIC: direct API bypass: Test direct endpoint access with anon/authenticated credentials.
• Default Function EXECUTE to PUBLIC: direct API bypass: Restrict exposed schemas, grants, and callable routines deliberately.
• Re-test after every migration that touches security-critical tables or functions.

How to fix Default Function EXECUTE to PUBLIC (backend-only + zero-policy posture)

Mockly’s safest default is backend-only access: the browser should not query tables, call RPC, or access Storage directly.

1. Decide which operations must remain client-side (often: none for sensitive resources).
2. Create server endpoints (API routes or server actions) for required reads/writes.
3. Apply hardening SQL: enable+force RLS where relevant, remove broad policies, and revoke grants from client roles.
4. Generate signed URLs for private Storage downloads on the server only.
5. Re-run a scan and confirm the issue disappears.
6. Add a regression check to your release process so drift doesn’t reintroduce exposure. Fixes that worked in linked incidents:

• Default Function EXECUTE to PUBLIC: direct API bypass: The team removed direct sensitive paths from client reach, tightened role grants and policy predicates, and added endpoint-level verification tests that run in CI after each migration.
• Default Function EXECUTE to PUBLIC: migration drift regression: The team added migration-time policy/grant diff checks, blocked deploys on drift findings, and required post-deploy direct-access verification for each changed surface.

Verification checklist for Default Function EXECUTE to PUBLIC

1. Attempt direct access using client credentials and confirm it fails.
2. Apply a backend-only fix pattern and verify end-to-end behavior.
3. Re-run a scan after changes and after the next migration.
4. Default Function EXECUTE to PUBLIC: direct API bypass: Frontend checks are UX, not authorization.
5. Default Function EXECUTE to PUBLIC: direct API bypass: Test direct endpoint access with anon/authenticated credentials.
6. Default Function EXECUTE to PUBLIC: direct API bypass: Restrict exposed schemas, grants, and callable routines deliberately.
7. Default Function EXECUTE to PUBLIC: direct API bypass: Keep one repeatable verification check per risk class in CI.
8. Default Function EXECUTE to PUBLIC: migration drift regression: Most recurring exposure comes from migration drift, not one-time coding mistakes.

SQL sanity checks for Default Function EXECUTE to PUBLIC (optional, but high signal)

If you prefer evidence over intuition, run a small set of SQL checks after each fix.

The goal is not to memorize catalog tables — it’s to make sure the access boundary you intended is the one Postgres actually enforces:

• Confirm RLS is enabled (and forced where appropriate) for tables tied to this term.
• List policies and read them as plain language: who can do what, under what condition?
• Audit grants for anon/authenticated and PUBLIC on the tables, views, and functions involved.
• If Storage is involved: review bucket privacy and policies for listing/reads.
• If RPC is involved: review EXECUTE grants for functions and whether privileged functions are server-only.

Pair these checks with a direct API access test using client credentials. When both agree, you can ship the fix with confidence.

Over time, keep a small “query pack” for the checks you trust and run it after every migration. That’s how you prevent quiet regressions.

Prevent Default Function EXECUTE to PUBLIC drift (so it doesn’t come back)

• Add a repeatable checklist and re-run it after schema changes.
• Prefer backend-only access for sensitive resources.
• Keep one reusable verification test for “Default Function EXECUTE to PUBLIC: direct API bypass” and rerun it after every migration that touches this surface.
• Keep one reusable verification test for “Default Function EXECUTE to PUBLIC: migration drift regression” and rerun it after every migration that touches this surface.

Rollout plan for Default Function EXECUTE to PUBLIC fixes (without breaking production)

Many hardening changes fail because teams revoke direct access first and only later discover missing backend paths.

Use this sequence to reduce both risk and outage pressure:

1. Implement and verify the backend endpoint or server action before permission changes.
2. Switch clients to that backend path behind a feature flag when possible.
3. Then revoke direct client access (broad grants, permissive policies, public bucket reads, or broad EXECUTE).
4. Run direct-access denial tests and confirm authorized backend flows still succeed.
5. Re-scan after deployment and again after the next migration.

This turns security fixes into repeatable rollout mechanics instead of one-off emergency changes.

Incident breakdowns for Default Function EXECUTE to PUBLIC (real scenarios)

Default Function EXECUTE to PUBLIC: direct API bypass

Scenario: A team validates behavior only through UI flows, but an attacker calls the underlying Supabase endpoint directly with client credentials. Because default function execute to public is present, the attacker can read or trigger operations outside intended authorization boundaries.

What failed: Security controls depended on frontend behavior and partial configuration checks. The underlying grants, schema exposure, or policy predicates still allowed direct access patterns that untrusted clients could reproduce.

What fixed it: The team removed direct sensitive paths from client reach, tightened role grants and policy predicates, and added endpoint-level verification tests that run in CI after each migration.

Why the fix worked: The fix enforces least privilege at the data boundary and validates attacker-like request paths instead of trusting UI constraints. This closes the bypass route and keeps behavior stable across refactors.

Key takeaways:

• Frontend checks are UX, not authorization.
• Test direct endpoint access with anon/authenticated credentials.
• Restrict exposed schemas, grants, and callable routines deliberately.
• Keep one repeatable verification check per risk class in CI.

Read full example: Default Function EXECUTE to PUBLIC: direct API bypass

Default Function EXECUTE to PUBLIC: migration drift regression

Scenario: The team previously hardened this area, but a later migration adds objects, privileges, or settings without full security review. The rollout reopens default function execute to public and restores an exploitable path in production.

What failed: Migrations were treated as schema-only changes without mandatory security gates. No automated checks validated grants, exposed schema settings, or authorization behavior before deployment.

What fixed it: The team added migration-time policy/grant diff checks, blocked deploys on drift findings, and required post-deploy direct-access verification for each changed surface.

Why the fix worked: Security posture becomes part of delivery quality controls, so regressions are caught before users are exposed. Drift no longer accumulates silently between releases.

Key takeaways:

• Most recurring exposure comes from migration drift, not one-time coding mistakes.
• Automate grant and policy checks in CI/CD.
• Treat API surface changes as security-sensitive deploy events.
• Re-run scans immediately after schema or auth changes.

Read full example: Default Function EXECUTE to PUBLIC: migration drift regression

Real-world examples of Default Function EXECUTE to PUBLIC (and why they work)

• Default Function EXECUTE to PUBLIC: direct API bypass — A production-like scenario where Default Function EXECUTE to PUBLIC is exploited through direct requests that bypass frontend assumptions.
• Default Function EXECUTE to PUBLIC: migration drift regression — A release regression where migration drift silently reintroduces default function execute to public after an earlier fix.

Related terms

• Default Privilege Drift → /glossary/default-privilege-drift
• Public RPC Surface Area → /glossary/public-rpc-surface-area