Why Can’t My User Access S3 Even with Full Permissions?

A permissions boundary doesn’t grant permissions; it just sets the limits for what the user *could* do. You'll need to attach an IAM policy that specifically grants access to S3. Make sure that policy is attached directly to the user or their group instead of just being in the boundary.

Can you share the policy details you’re using? It might help to see what you've set up to better troubleshoot.

Think of it this way: a permission boundary is the maximum permissions you can grant, but it doesn’t automatically give them. By putting S3 full access as a boundary, you're saying that the policy can grant those permissions at best, but doesn’t actually give them right away.

Remember, a permissions boundary restricts access, it doesn’t provide it. Even if you attach an S3 full access policy, if it's only set as a boundary, it won't actually give the user any permissions. You need to attach that policy as a managed or inline policy for the user to get access.