I’m using an S3 REST API endpoint as the origin of my CloudFront distribution. Why am I getting 403 Access Denied errors?

Last updated: 2019-07-30

I'm using an Amazon Simple Storage Service (Amazon S3) bucket as the origin of my Amazon CloudFront distribution. I'm using the S3 REST API endpoint as the origin domain name. Why is CloudFront returning 403 Access Denied errors from Amazon S3?

Short Description

To troubleshoot Access Denied errors, you must know if your distribution’s origin domain name is an S3 website endpoint or an S3 REST API endpoint. Follow these steps to determine the endpoint type:

  1. Open the CloudFront console.
  2. Select your CloudFront distribution, then choose Distribution Settings.
  3. Choose the Origins tab.
  4. Review the domain name under Origin Domain Name and Path. Then, determine the endpoint type based on the format of the domain name.

REST API endpoints use this format:

awsexamplebucket.s3.amazonaws.com

Static website endpoints use this format:

awsexamplebucket.s3-website-us-east-1.amazonaws.com

If your distribution is using an S3 static website endpoint, see I'm using an S3 website endpoint as the origin of my CloudFront distribution. Why am I getting 403 Access Denied errors?

If your distribution is using a REST API endpoint, verify that your configurations meet the following requirements to avoid Access Denied errors:

  • If you don't configure an origin access identity (OAI), the objects must be publicly accessible or requested with AWS Signature Version 4.
  • If you're using encryption with AWS Key Management Service (AWS KMS), your configuration must support KMS-encrypted objects.
  • The S3 bucket policy must allow access to s3:GetObject.
  • If the bucket policy grants access, the AWS account that owns the S3 bucket must also own the object.
  • The requested objects must exist in the S3 bucket.
  • If clients request the root of your distribution, you must define a default root object.
  • If you configured an OAI, the OAI must be included in the S3 bucket policy.
  • If you didn't configure an OAI, Amazon S3 block public access settings must be disabled.

Resolution

If you don't configure an OAI, the objects must be publicly accessible or requested with AWS Signature Version 4

If you don't configure an OAI, a distribution using a REST API endpoint supports only public objects, or objects requested with AWS Signature Version 4 authentication.

To determine if the objects in your S3 bucket are publicly accessible, open the S3 object's URL in a web browser. Or, you can run a curl command on the URL.

The following is an example URL of an S3 object:

http://awsexamplebucket.s3-website-us-east-1.amazonaws.com/index.html

If either the web browser or curl command returns an Access Denied error, then the object isn't publicly accessible. If the object isn't publicly accessible, use one of the following configurations:

If you're using encryption with AWS KMS, your configuration must support KMS-encrypted objects

If a distribution is using a REST API endpoint and an OAI, then the distribution doesn't support KMS-encrypted objects. If a distribution is using a REST API endpoint but not an OAI, then the distribution supports KMS-encrypted objects only for requests with AWS Signature Version 4. The requester must also have access to the KMS key used to encrypt the object.

Use one of the following ways to check if an object in your bucket is KMS-encrypted:

  • Use the Amazon S3 console to view the properties of the object. Review the Encryption dialog box. If AWS-KMS is selected, then the object is KMS-encrypted.
  • Run the head-object command using the AWS Command Line Interface (AWS CLI). If the command returns ServerSideEncryption as aws:kms, then the object is KMS-encrypted.

To change the object's encryption settings using the Amazon S3 console, see How Do I Add Encryption to an S3 Object?

To change the object's encryption settings using the AWS CLI, first verify that the object's bucket doesn't have default encryption. If the bucket doesn't have default encryption, run the following AWS CLI command to remove the object's encryption by copying the object over itself.

Warning: Copying the object over itself removes settings for storage-class and website-redirect-location. To maintain these settings in the new object, be sure to explicitly specify storage-class or website-redirect-location values in the copy request. For more information, see Request Headers.

aws s3 cp s3://awsexamplebucket/index.html s3://awsexamplebucket/index.html

The S3 bucket policy must allow access to s3:GetObject

To use a distribution with an S3 REST API endpoint, your bucket policy must allow s3:GetObject either to public users or to CloudFront's OAI.

Even if you have an explicit allow statement for s3:GetObject in your bucket policy, confirm that there isn't a conflicting explicit deny statement. An explicit deny statement always overrides an explicit allow statement.

Follow these steps to review your bucket policy for s3:GetObject:

1.    Open your S3 bucket from the Amazon S3 console.

2.    Choose the Permissions tab.

3.    Choose Bucket Policy.

4.    Review the bucket policy for statements with "Action": "s3:GetObject" or "Action": "s3:*".

In the following example policy, there's an allow statement that grants a CloudFront OAI access to s3:GetObject. There's also an allow statement that grants public access to s3:GetObject. However, there's an explicit deny statement for s3:GetObject that blocks access unless the request is from a specific Amazon Virtual Private Cloud (Amazon VPC).

{
  "Version": "2008-10-17",
  "Id": "PolicyForCloudFrontPrivateContent",
  "Statement": [{
      "Sid": "Allow-OAI-Access-To-Bucket",
      "Effect": "Allow",
      "Principal": {
        "AWS": "arn:aws:iam::cloudfront:user/CloudFront OAI EAF5XXXXXXXXX"
      },
      "Action": "s3:GetObject",
      "Resource": [
        "arn:aws:s3:::awsexamplebucket/*"
      ]
    },
    {
      "Sid": "Allow-Public-Access-To-Bucket",
      "Effect": "Allow",
      "Principal": "*",
      "Action": "s3:GetObject",
      "Resource": [
        "arn:aws:s3:::awsexamplebucket/*"
      ]
    },
    {
      "Sid": "Access-to-specific-VPCE-only",
      "Effect": "Deny",
      "Principal": "*",
      "Action": "s3:GetObject",
      "Resource": [
        "arn:aws:s3:::awsexamplebucket/*"
      ],
      "Condition": {
        "StringNotEquals": {
          "aws:sourceVpce": "vpce-1a2b3c4d"
        }
      }
    }
  ]
}

5.    Modify the bucket policy to remove or edit statements that block CloudFront OAI access or public access to s3:GetObject.

Note: CloudFront caches the results of an Access Denied error for up to 5 minutes. After removing a deny statement from the bucket policy, you can run an invalidation on your distribution to remove the object from the cache.

If the bucket policy grants access, the AWS account that owns the S3 bucket must also own the object

For a bucket policy to apply to external accounts or services (for example, public access or OAI), the AWS account that owns the bucket must also own the objects. A bucket or object is owned by the account of the AWS Identity and Access Management (IAM) identity that created the bucket or object.

Note: The object-ownership requirement applies to access granted by a bucket policy. It doesn't apply to access granted by the object's access control list (ACL).

Follow these steps to check if the bucket and objects have the same owner:

1.    Run this AWS CLI command to get the S3 canonical ID of the bucket owner:

aws s3api list-buckets --query Owner.ID

2.    Run this command to get the S3 canonical ID of the object owner.

Note: This example shows a single object, but you can use the list command to check several objects.

aws s3api list-objects --bucket awsexamplebucket --prefix index.html

3.    If the canonical IDs don't match, then the bucket and object have different owners.

Note: You can also use the Amazon S3 console to check the bucket and object owners. The owners are found in the Permissions tab of the respective bucket or object.

Follow these steps to change the object's owner to the bucket owner:

1.    From the object owner's AWS account, run this command to retrieve the access control list (ACL) permissions assigned to the object:

aws s3api get-object-acl --bucket awsexamplebucket --key object-name

2.    If the object has bucket-owner-full-control ACL permissions, then skip to step #3. If the object doesn't have bucket-owner-full-control ACL permissions, then run this command from the object owner's account:

aws s3api put-object-acl --bucket awsexamplebucketname --key object-name --acl bucket-owner-full-control

3.    Run this command to change the owner of the object by copying the object over itself:

aws s3 cp s3://awsexamplebucket/index.html s3://awsexamplebucket/index.html

The requested objects must exist in the bucket

If a user doesn't have s3:ListBucket permissions, then the user gets Access Denied errors for missing objects instead of 404 Not Found errors. Run the head-object AWS CLI command to check if an object exists in the bucket.

Note: Confirm that the object request sent to CloudFront matches the S3 object name exactly. S3 object names are case-sensitive. If the request doesn't have the correct object name, then Amazon S3 responds as though the object is missing. To identify which object CloudFront is requesting from Amazon S3, use server access logging.

If the object exists in the bucket, then the Access Denied error isn't masking a 404 Not Found error. Verify other configuration requirements to resolve the Access Denied error.

If the object isn’t in the bucket, then the Access Denied error is masking a 404 Not Found error. Resolve the issue related to the missing object.

Note: We don't recommend enabling public s3:ListBucket access, because it's not a security best practice.

If clients request the root of your distribution, you must define a default root object

If your distribution doesn't have a default root object defined, and a requester doesn't have s3:ListBucket access, then the requester receives an Access Denied error. The requester gets this error instead of a 404 Not Found error when they request the root of your distribution.

To define a default root object, see Specifying a Default Root Object.

Note: We don't recommend enabling public s3:ListBucket access because it's not a security best practice.

If you configured an OAI, the OAI must be included in the S3 bucket policy

If you added an OAI to your CloudFront distribution, you must also include an allow statement for the OAI in the S3 bucket policy.

To verify if your bucket policy allows the OAI, open your S3 bucket in the Amazon S3 console. Then, choose the Permissions tab and review the bucket policy. The following is an example allow statement for an OAI:

{
  "Sid": "1",
  "Effect": "Allow",
  "Principal": {
    "AWS": "arn:aws:iam::cloudfront:user/CloudFront OAI EAF5XXXXXXXXX"
  },
  "Action": "s3:GetObject",
  "Resource": "arn:aws:s3:::awsexamplebucket/*"
}

To update your bucket policy using the CloudFront console, follow these steps:

  1. Open the CloudFront console and choose your distribution.
  2. Choose the Origins tab.
  3. Select the S3 origin and choose Edit.
  4. For Restrict Bucket Access, choose Yes.
  5. For Origin Access Identity, choose the existing identity or create a new one.
  6. For Grant Read Permissions on Bucket, choose Yes, Update Bucket Policy.
  7. Choose Yes, Edit.

If you didn't configure an OAI, Amazon S3 block public access settings must be disabled

If the distribution isn't using an OAI, and objects aren't requested with AWS Signature Version 4, then the distribution with a REST API endpoint supports only public objects. This means that you must confirm that there aren't any Amazon S3 block public access settings applied to the bucket. These settings can override permissions that allow public access. Block public access settings can apply to individual buckets or AWS accounts.