Realtime Public Channel Mode

What “Realtime Public Channel Mode” means (plain English)

Realtime Public Channel Mode means anyone with client credentials can join channels that were meant to be restricted. Even if your UI hides channel names, attackers can script subscriptions directly. Without private channels and authorization checks, notifications, presence data, or event payloads can leak across users or tenants.

How Realtime Public Channel Mode works in Supabase/Postgres (technical)

Supabase Realtime supports public and private channels. In production, weak posture appears when Allow public access stays enabled, clients subscribe without private: true, and RLS policies on realtime.messages do not enforce topic-specific constraints. Hardening requires private channel mode, authorization policies keyed by realtime.topic(), and periodic tests for unauthorized subscribe/broadcast/presence actions.

Attack paths & failure modes for Realtime Public Channel Mode

• Realtime Public Channel Mode: direct API bypass: A team validates behavior only through UI flows, but an attacker calls the underlying Supabase endpoint directly with client credentials. Because realtime public channel mode is present, the attacker can read or trigger operations outside intended authorization boundaries.
• Realtime Public Channel Mode: 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 realtime public channel mode and restores an exploitable path in production.
• Realtime Public Channel Mode: 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.
• Realtime Public Channel Mode: 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 Realtime Public Channel Mode matters for Supabase security

Realtime leaks are high-speed and hard to notice because traffic looks like normal websocket activity. Misconfigured channel access can expose live operational data, membership state, or record updates at scale. Correct channel authorization protects tenant boundaries and prevents passive eavesdropping.

Common Realtime Public Channel Mode mistakes that lead to leaks

• Using topic naming conventions as security instead of enforcing private channel authorization rules.
• Keeping public channel mode enabled for convenience after launch without strict RLS policies.
• Testing only happy-path subscriptions and never verifying unauthorized channel joins.
• Realtime Public Channel Mode: 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.
• Realtime Public Channel Mode: 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 Realtime Public Channel Mode in Supabase

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

How to detect Realtime Public Channel Mode 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.
• Realtime Public Channel Mode: direct API bypass: Frontend checks are UX, not authorization.
• Realtime Public Channel Mode: direct API bypass: Test direct endpoint access with anon/authenticated credentials.
• Realtime Public Channel Mode: 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 Realtime Public Channel Mode (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:

• Realtime Public Channel Mode: 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.
• Realtime Public Channel Mode: 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 Realtime Public Channel Mode

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. Realtime Public Channel Mode: direct API bypass: Frontend checks are UX, not authorization.
5. Realtime Public Channel Mode: direct API bypass: Test direct endpoint access with anon/authenticated credentials.
6. Realtime Public Channel Mode: direct API bypass: Restrict exposed schemas, grants, and callable routines deliberately.
7. Realtime Public Channel Mode: direct API bypass: Keep one repeatable verification check per risk class in CI.
8. Realtime Public Channel Mode: migration drift regression: Most recurring exposure comes from migration drift, not one-time coding mistakes.

SQL sanity checks for Realtime Public Channel Mode (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 Realtime Public Channel Mode 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 “Realtime Public Channel Mode: direct API bypass” and rerun it after every migration that touches this surface.
• Keep one reusable verification test for “Realtime Public Channel Mode: migration drift regression” and rerun it after every migration that touches this surface.

Rollout plan for Realtime Public Channel Mode 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 Realtime Public Channel Mode (real scenarios)

Realtime Public Channel Mode: 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 realtime public channel mode 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: Realtime Public Channel Mode: direct API bypass

Realtime Public Channel Mode: 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 realtime public channel mode 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: Realtime Public Channel Mode: migration drift regression

Real-world examples of Realtime Public Channel Mode (and why they work)

• Realtime Public Channel Mode: direct API bypass — A production-like scenario where Realtime Public Channel Mode is exploited through direct requests that bypass frontend assumptions.
• Realtime Public Channel Mode: migration drift regression — A release regression where migration drift silently reintroduces realtime public channel mode after an earlier fix.

Related terms

• Realtime Channel Authorization Gap → /glossary/realtime-channel-authorization-gap
• Realtime Presence Data Leak → /glossary/realtime-presence-data-leak