How to Fix Amazon S3 403 Access Denied Errors

If you've encountered a 403 Access Denied error when trying to access files in an Amazon S3 bucket, you're not alone. This is a common issue that can be frustrating but is usually fixable with the right approach. In this guide, we'll explain the problem and the solution in a straightforward manner.

The Problem: Why You Get a 403 Access Denied Error in S3

The 403 Access Denied error means that you (or your users) do not have the necessary permissions to access the S3 bucket or its objects. This can be caused by:

1. Missing Bucket Policy or Object Permissions – The S3 bucket or objects do not have the correct permissions set.
2. Incorrect IAM Policies – The IAM user or role does not have the required permissions to access the S3 bucket.
3. Blocked Public Access Settings – If public access is disabled, requests that rely on public permissions will fail.
4. Mismatched AWS Region or Endpoint – Trying to access an S3 bucket from the wrong region or using an incorrect endpoint.
5. S3 Object Ownership Issues – Objects uploaded by a different AWS account may not be accessible due to default ownership settings.
6. KMS Encryption Restrictions – If an S3 object is encrypted with AWS KMS, the user must have permissions to decrypt it.

The Solution: How to Fix 403 Access Denied Errors

Here’s a step-by-step approach to troubleshooting and fixing this issue:

1. Check and Update the S3 Bucket Policy

• Go to the AWS S3 console.
• Navigate to the Permissions tab.
• Under Bucket Policy, ensure that the correct access permissions are granted.
• Example policy to allow public read access: Replace your-bucket-name with your actual bucket name.

{
"Version": "2012-10-17",
"Statement": [
{
"Effect": "Allow",
"Principal": "*",
"Action": "s3:GetObject",
"Resource": "arn:aws:s3:::your-bucket-name/*"
}
]
}

2. Verify IAM Permissions

• Go to the AWS IAM Console.
• Check the IAM user or role accessing the S3 bucket.
• Ensure the IAM policy includes permissions like:

{
"Effect": "Allow",
"Action": "s3:GetObject",
"Resource": "arn:aws:s3:::your-bucket-name/*"
}

• If using an IAM Role, verify that the role is correctly attached to the instance or service.

3. Adjust Block Public Access Settings

• In the S3 console, navigate to the Permissions tab.
• Under Block Public Access settings, ensure the settings match your use case.
• If you need public access, uncheck "Block all public access" (only if safe to do so).

4. Use the Correct AWS Region and Endpoint

• Ensure you are using the correct region for the bucket.
• Example of specifying a region in the AWS CLI:

aws s3 ls s3://your-bucket-name --region us-east-1

• If using SDKs, explicitly set the region in your configuration.

5. Fix S3 Object Ownership Issues

• Go to the Objects tab in S3.
• Check if the object ownership is set to Bucket owner preferred.
• If objects were uploaded by a different AWS account, use the s3:PutObjectAcl permission to grant access.

6. Check KMS Encryption Settings

• If your S3 objects are encrypted with AWS KMS, ensure:
  • The user has the kms:Decrypt permission.
  • The IAM policy allows KMS access.
  • The correct KMS key is being used.

Final Thoughts

The 403 Access Denied error in Amazon S3 is usually related to misconfigured permissions, public access settings, or IAM policies. By systematically checking these areas, you can quickly resolve the issue and restore access.

If you’re still facing issues, consider using AWS CloudTrail logs to trace access attempts or AWS Trusted Advisor to check for security misconfigurations.