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A 400 response from a Supabase Storage upload does not by itself prove that the Dashboard created a policy on the wrong table. Storage authorization policies apply to storage.objects, and Supabase’s current quickstart says you can create them in either the Dashboard or SQL Editor. In one reported case, an upload returned Invalid Compact JWS until the author recreated bucket-scoped policies in SQL; that is a useful debugging account, not proof that the Dashboard is generally unreliable.
What the reported upload failure looked like
Lior Karaev described uploading a CV to a private cvs bucket for a job board. The client saw HTTP 400, while the response body said {"statusCode":"403","error":"Unauthorized","message":"Invalid Compact JWS"}. The author reports trying anonymous INSERT, authenticated SELECT, and authenticated DELETE policies through the Storage UI, then checking bucket size and MIME limits, client initialization, filename and path, and content type. The failure persisted. After creating bucket-scoped policies directly on storage.objects in the SQL Editor, the author says the upload worked. Read the reported debugging account.
The report’s diagnosis should be treated cautiously. Supabase’s current quickstart explicitly describes creating policies in the Dashboard or with SQL, and its Dashboard steps refer to the OBJECTS table. SQL can make a policy easier to inspect and define precisely, but the available documentation does not establish that Dashboard-created policies generally target the wrong layer.
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Supabase applies Storage access control through row-level security (RLS) policies on storage.objects. A policy usually limits its rows with a predicate such as bucket_id = 'cvs'; a bucket condition alone does not restrict access to a particular user or file. The Storage access-control guide documents these operation requirements:
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| Operation | Documented policy requirements | What to scope |
|---|---|---|
| Upload a new object | INSERT | Who may upload, to which bucket, and which object paths. |
| Upsert an object | INSERT, SELECT, and UPDATE | Who may create or replace the object, and which paths are eligible. |
| Read or list objects | SELECT | Which users may see object metadata or retrieve files. |
| Delete an object | DELETE | Which users may remove which objects. |
The Python upload reference also lists the upsert requirements; the exact API call and language do not make a new upload equivalent to an upsert. Check whether your client sends an upsert before adding policies for it. Supabase Python upload reference.
Debug the error before widening access
- Read the response precisely. Record both the HTTP status and response body.
Invalid Compact JWS,403 Unauthorized, andnew row violates row-level security policyare not interchangeable messages. Supabase documents distinct error codes for invalid JWTs, access denied, missing buckets or keys, and file-size violations. Use the Storage error-code reference to narrow the failure. - Confirm the identity reaching Storage. Verify whether the request is using the intended anonymous or authenticated role and that an expected user JWT is actually present. A policy for
authenticatedcannot authorize a request that reaches the API asanon. - Check the exact target. Confirm the bucket ID and object path sent by the client, including capitalization and any path segments used in policy conditions. Check that the bucket exists and that the requested operation is allowed by its configuration.
- Identify the operation. Distinguish a new upload from an upsert, and separately account for any subsequent read, list, or delete request. A successful insert does not automatically grant those other permissions.
- Inspect effective policies and grants. Review policies on
storage.objectsfor the operation and role in question. RLS policies are not the same as SQL privileges: a missing grant can stop a request before a policy is evaluated. Supabase explains the distinction in its RLS documentation. - Only then change policy scope. If a policy is wrong or missing, correct the role, operation, bucket, identity, and path conditions. SQL is a useful way to make those rules explicit, but changing the editor is not a substitute for verifying what policy is effective.
When an upload error mentions row-level security
Supabase documents a specific 403 case in which an upload fails with new row violates row-level security policy. Its troubleshooting guide explains that a suitable SELECT policy may be needed so the Storage API can return metadata for the inserted object, and recommends matching SELECT scope to the intended INSERT access. This is a separate documented explanation from the reported Invalid Compact JWS response; do not infer that every failed upload needs broader read access. See Supabase’s 403 upload troubleshooting guide.
Why the reported SQL is not a safe default
The account’s sample policies allowed anonymous clients to insert into the cvs bucket and allowed any authenticated user to select or delete objects there. That may demonstrate the author’s reported workaround, but it is broad: a bucket-wide SELECT can expose other people’s files, and bucket-wide DELETE can let users remove files they do not own. The author later acknowledged risks in the assumptions, including orphaned uploads, and comments describe movement toward signed upload URLs and tighter policy state.
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Design each policy around the application’s actual authorization rule. Limit the role, bucket, user identity, object path, and operation as appropriate; do not grant read or delete access simply to make an upload succeed. Supabase documents owner_id as the current ownership field for policy checks and says the older owner field is deprecated. Ownership is useful in a predicate, but it is not an access rule unless a policy uses it. See the ownership guidance.
For especially sensitive uploads, consider a design in which a trusted server authorizes the upload and issues a short-lived signed upload URL, rather than opening a bucket-wide anonymous write policy. The appropriate design depends on how the application validates users and associates uploaded files with records.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Use SQL for policy precision, not direct metadata edits
If you choose SQL, create or revise RLS policies on the documented storage.objects surface and express the intended access conditions there. Do not repair an upload by directly inserting, updating, or deleting rows in Storage metadata tables. Supabase stores file metadata in Postgres while the file contents live in an underlying storage provider; its Storage schema guide recommends treating the Storage schema as read-only for file operations and using the Storage API for upload, copy, move, and delete.
Never put a service key in browser code to bypass RLS. Supabase notes that service keys bypass RLS and should not be shared publicly. Keep privileged credentials on a trusted server and give browser clients only the narrowly scoped access the application requires. Storage access control.
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