S3 Access Denied Troubleshooting: Every Cause and How to Fix It (2026)

If you are staring at An error occurred (AccessDenied) when calling the GetObject operation: Access Denied , this guide walks through every cause in the order you should check them, with the exact fix for each. I am a cloud associate and I debug this error often enough that I keep a mental checklist. Here it is, written down. Quick answer: the 8 most common causes of S3 Access Denied In Amazon S3, "Access Denied" means the request was authenticated but not authorized, or an explicit deny blocked it. In practice it is almost always one of these, roughly in order of frequency: The IAM identity (user or role) is missing the required s3: permission. The bucket policy does not allow the action, or explicitly denies it. S3 Block Public Access is on and you expected public/anonymous access. SSE-KMS : you have S3 permission but not kms:Decrypt on the encryption key. Missing s3:ListBucket , which turns a "key not found" into a 403. Cross-account access where only one side grants permission. An explicit Deny somewhere wins (SCP, permissions boundary, VPC endpoint policy, or bucket policy). Object ownership / ACLs after a cross-account upload. If you only remember one thing: an explicit Deny anywhere in the chain always beats an Allow . Start by finding a deny, then work down the list. Step 0: Confirm which identity is actually making the request Before touching any policy, confirm who you are. Most "but I have admin" cases are the wrong principal. aws sts get-caller-identity Check the Arn in the output. If it is a role you did not expect (an EC2 instance profile, a CI role, an assumed role), you have been debugging the wrong identity's permissions the whole time. This single command saves more time than any other step. Step 1: Does the IAM identity policy allow the action? S3 needs the specific action for the specific resource. The two resource types trip people up: Bucket-level actions ( s3:ListBucket , s3:GetBucketLocation ) target the bucket ARN: arn:aws:s3:::my-bucket Obj