Supabase RLS bug classes — reference

This page catalogs the RLS bug classes that don’t get full case studies in the Inbox sample. One paragraph per bug, one short SqlProof property snippet, plus an audit-style snippet for the schema-level ones.

For the fuller, recipe-style treatment of the most-impactful RLS bugs (tenant scoping in SECURITY DEFINER RPCs, uncorrelated EXISTS, missing WITH CHECK, missing DELETE policies, internal-vs-public message gating), see the Inbox sample recipes.

Over-permissive policy (`USING (true)`)

A policy USING (true) on a SELECT/INSERT/UPDATE/DELETE grants the operation to any caller in the policy’s role. Sometimes intentional for public-read tables, often a copy-paste error from a “make it work first” prototype.

@given(data=st.data())
def test_policy_excludes_some_rows(supabase_proof, data):
    # If the policy is restrictive at all, at least one non-owner should
    # see fewer rows than the owner. If they see all rows, the policy is
    # equivalent to USING (true).
    ...

UPDATE policy without a paired SELECT policy

PostgreSQL evaluates UPDATE policies by first reading the row (via the SELECT policy chain). With no SELECT policy on the table, the read returns nothing, and the UPDATE silently affects zero rows even for the owner.

def test_owner_update_actually_modifies_the_row(supabase_proof, data):
    with as_rls_user(db, owner_id):
        db.execute("UPDATE table SET col = %s WHERE id = %s", new_val, row_id)
    after = db.scalar("SELECT col FROM table WHERE id = %s", row_id)
    assert after == new_val   # fails silently if SELECT policy missing

`security_invoker` view bypass

Pre-PG15, views run as their creator (often postgres), so the underlying table’s RLS is ignored. In PG15+ create views with WITH (security_invoker = true).

def test_view_respects_underlying_rls(supabase_proof, data):
    with as_rls_user(db, non_owner_id):
        via_view  = db.query("SELECT id FROM the_view WHERE id = %s", row_id)
        direct    = db.query("SELECT id FROM the_table WHERE id = %s", row_id)
    assert via_view == direct

`user_metadata` trust

Supabase exposes auth.jwt() -> 'user_metadata' as JWT claims that the client can write. Policies that trust user_metadata->>'role' = 'admin' are bypassable; use app_metadata (server-only) or a database table.

SqlProof’s as_supabase_user accepts an extra_claims= arg, so you can directly test that a user with an admin claim in user_metadata doesn’t gain admin powers:

with as_rls_user(db, user_id, extra_claims={"user_metadata": {"role": "admin"}}):
    rows = db.query("SELECT * FROM admin_only_table")
assert rows == []   # if the policy correctly ignores user_metadata

Infinite policy recursion

A policy on table A that references table B, whose policy references table A, can cause PostgreSQL to recurse until stack depth limit exceeded. The property: every policy-gated query completes within a reasonable budget.

def test_policy_query_does_not_recurse(supabase_proof, data):
    with as_rls_user(db, user_id):
        db.query("SELECT id FROM table_a LIMIT 1")
    # If we reach here, no stack overflow.

The Inbox sample’s Recipe 2 includes a comment about this pattern — the recursive form of org_members self-reference is exactly this class.

Schema-level audits (one-shot, not property tests)

These are introspection queries, not invariants — run them once per CI build to enforce shop-wide RLS hygiene.

Every public table has RLS enabled

def test_every_public_table_has_rls(db):
    rows = db.query("""
        SELECT c.relname FROM pg_class c
        JOIN pg_namespace n ON n.oid = c.relnamespace
        WHERE c.relkind = 'r' AND n.nspname = 'public' AND NOT c.relrowsecurity
    """)
    assert rows == [], f"tables without RLS: {[r['relname'] for r in rows]}"

Every policy specifies a `TO` clause

def test_every_policy_targets_a_role(db):
    rows = db.query("""
        SELECT schemaname, tablename, policyname
        FROM pg_policies
        WHERE roles = '{public}'   -- public means "all roles", almost always a mistake
    """)
    assert rows == []

Every `SECURITY DEFINER` function pins `search_path`

def test_security_definer_functions_lock_search_path(db):
    rows = db.query("""
        SELECT n.nspname, p.proname
        FROM pg_proc p JOIN pg_namespace n ON n.oid = p.pronamespace
        WHERE p.prosecdef = true
          AND n.nspname = 'public'
          AND (p.proconfig IS NULL
               OR NOT EXISTS (SELECT 1 FROM unnest(p.proconfig) c WHERE c LIKE 'search_path=%'))
    """)
    assert rows == []

When SqlProof ships issue #77 (planned sqlproof.contrib.supabase.audit module), these snippets will become one-liners like assert_rls_enabled(db, "tickets") and tables_without_rls(db) == set().

Identity / silent-fail bugs

When auth.uid() returns NULL (anonymous request) and a policy like USING (auth.uid() = user_id) evaluates to NULL → false, the API returns an empty result. Test the anonymous path explicitly — see SqlProof issue #78 for the planned as_anonymous() helper; today’s workaround:

db.execute("SET LOCAL ROLE anon")
try:
    rows = db.query("SELECT * FROM tickets")
finally:
    db.execute("RESET ROLE")
assert rows == []

Supabase RLS bug classes — reference

Over-permissive policy (USING (true))