How Amazon S3 works with IAM

Before you use IAM to manage access to Amazon S3, learn what IAM features are available to use with Amazon S3.

To get a high-level view of how Amazon S3 and other AWS services work with most IAM features, see AWS services that work with IAM in the IAM User Guide.

For more information about the permissions to S3 API operations by S3 resource types, see Required permissions for Amazon S3 API operations.

Identity-based policies for Amazon S3

Supports identity-based policies: Yes

Identity-based policies are JSON permissions policy documents that you can attach to an identity, such as an IAM user, group of users, or role. These policies control what actions users and roles can perform, on which resources, and under what conditions. To learn how to create an identity-based policy, see Define custom IAM permissions with customer managed policies in the IAM User Guide.

With IAM identity-based policies, you can specify allowed or denied actions and resources as well as the conditions under which actions are allowed or denied. You can't specify the principal in an identity-based policy because it applies to the user or role to which it is attached. To learn about all of the elements that you can use in a JSON policy, see IAM JSON policy elements reference in the IAM User Guide.

Identity-based policy examples for Amazon S3

To view examples of Amazon S3 identity-based policies, see Identity-based policies for Amazon S3.

Resource-based policies within Amazon S3

Supports resource-based policies: Yes

Resource-based policies are JSON policy documents that you attach to a resource. Examples of resource-based policies are IAM role trust policies and Amazon S3 bucket policies. In services that support resource-based policies, service administrators can use them to control access to a specific resource. For the resource where the policy is attached, the policy defines what actions a specified principal can perform on that resource and under what conditions. You must specify a principal in a resource-based policy. Principals can include accounts, users, roles, federated users, or AWS services.

To enable cross-account access, you can specify an entire account or IAM entities in another account as the principal in a resource-based policy. Adding a cross-account principal to a resource-based policy is only half of establishing the trust relationship. When the principal and the resource are in different AWS accounts, an IAM administrator in the trusted account must also grant the principal entity (user or role) permission to access the resource. They grant permission by attaching an identity-based policy to the entity. However, if a resource-based policy grants access to a principal in the same account, no additional identity-based policy is required. For more information, see Cross account resource access in IAM in the IAM User Guide.

The Amazon S3 service supports bucket policies, access points policies, and access grants:

Principals for bucket policies

The Principal element specifies the user, account, service, or other entity that is either allowed or denied access to a resource. The following are examples of specifying Principal. For more information, see Principal in the IAM User Guide.

Grant permissions to an AWS account

To grant permissions to an AWS account, identify the account using the following format.

"AWS":"account-ARN"

The following are examples.

"Principal":{"AWS":"arn:aws:iam::AccountIDWithoutHyphens:root"}

"Principal":{"AWS":["arn:aws:iam::AccountID1WithoutHyphens:root","arn:aws:iam::AccountID2WithoutHyphens:root"]}

Grant permissions to an IAM user

To grant permission to an IAM user within your account, you must provide an "AWS":"user-ARN" name-value pair.

"Principal":{"AWS":"arn:aws:iam::account-number-without-hyphens:user/username"}

For detailed examples that provide step-by-step instructions, see Example 1: Bucket owner granting its users bucket permissions and Example 3: Bucket owner granting permissions to objects it does not own.

Grant anonymous permissions

To grant permission to everyone, also referred as anonymous access, you set the wildcard ("*") as the Principal value. For example, if you configure your bucket as a website, you want all the objects in the bucket to be publicly accessible.

"Principal":"*"

"Principal":{"AWS":"*"}

Using "Principal": "*" with an Allow effect in a resource-based policy allows anyone, even if they’re not signed in to AWS, to access your resource.

Using "Principal" : { "AWS" : "*" } with an Allow effect in a resource-based policy allows any root user, IAM user, assumed-role session, or federated user in any account in the same partition to access your resource.

For anonymous users, these two methods are equivalent. For more information, see All principals in the IAM User Guide.

You cannot use a wildcard to match part of a principal name or ARN.

Restrict resource permissions

You can also use resource policy to restrict access to resources that would otherwise be available to IAM principals. Use a Deny statement to prevent access.

The following example blocks access if a secure transport protocol isn’t used:

{"Effect": "Deny", 
 "Principal": "*",
 "Action": "s3:*",
 "Resource": <bucket ARN>,
 "Condition": {
   "Boolean": { "aws:SecureTransport" : "false"}
 }
}

Using "Principal": "*" so that this restriction applies to everyone is a best practice for this policy, instead of attempting to deny access only to specific accounts or principals using this method.

Require access through CloudFront URLs

You can require that your users access your Amazon S3 content only by using CloudFront URLs instead of Amazon S3 URLs. To do this, create a CloudFront origin access control (OAC). Then, change the permissions on your S3 data. In your bucket policy, you can set CloudFront as the Principal as follows:

"Principal":{"Service":"cloudfront.amazonaws.com"}

Use a Condition element in the policy to allow CloudFront to access the bucket only when the request is on behalf of the CloudFront distribution that contains the S3 origin.

        "Condition": {
           "StringEquals": {
              "AWS:SourceArn": "arn:aws:cloudfront::111122223333:distribution/CloudFront-distribution-ID"
           }
        }
        

For more information about requiring S3 access through CloudFront URLs, see Restricting access to an Amazon Simple Storage Service origin in the Amazon CloudFront Developer Guide. For more information about the security and privacy benefits of using Amazon CloudFront, see Configuring secure access and restricting access to content.

Resource-based policy examples for Amazon S3

Policy actions for Amazon S3

Supports policy actions: Yes

Administrators can use AWS JSON policies to specify who has access to what. That is, which principal can perform actions on what resources, and under what conditions.

The Action element of a JSON policy describes the actions that you can use to allow or deny access in a policy. Policy actions usually have the same name as the associated AWS API operation. There are some exceptions, such as permission-only actions that don't have a matching API operation. There are also some operations that require multiple actions in a policy. These additional actions are called dependent actions.

Include actions in a policy to grant permissions to perform the associated operation.

The following shows different types of mapping relationship between S3 API operations and the required policy actions.

To see a list of Amazon S3 actions for use in policies, see Actions defined by Amazon S3 in the Service Authorization Reference. For a complete list of Amazon S3 API operations, see Amazon S3 API Actions in the Amazon Simple Storage Service API Reference.

For more information about the permissions to S3 API operations by S3 resource types, see Required permissions for Amazon S3 API operations.

Policy actions in Amazon S3 use the following prefix before the action:

s3

To specify multiple actions in a single statement, separate them with commas.

"Action": [
      "s3:action1",
      "s3:action2"
         ]

Bucket operations

Bucket operations are S3 API operations that operate on the bucket resource type. For example, CreateBucket, ListObjectsV2, and PutBucketPolicy. S3 policy actions for bucket operations require the Resource element in bucket policies or IAM identity-based policies to be the S3 bucket type Amazon Resource Name (ARN) identifier in the following example format.

"Resource": "arn:aws:s3:::amzn-s3-demo-bucket"

The following bucket policy grants the user Akua with account 12345678901 the s3:ListBucket permission to perform the ListObjectsV2 API operation and list objects in an S3 bucket.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "Allow Akua to list objects in the bucket",
            "Effect": "Allow",
            "Principal": {
                "AWS": "arn:aws:iam::12345678901:user/Akua"
            },
            "Action": [
            "s3:ListBucket"
            ],
            "Resource": "arn:aws:s3:::amzn-s3-demo-bucket"
        }
    ]
}

Bucket operations in access point policies

Permissions granted in an access point policy are effective only if the underlying bucket allows the same permissions. When you use S3 Access Points, you must delegate access control from the bucket to the access point or add the same permissions in the access point policies to the underlying bucket's policy. For more information, see Configuring IAM policies for using access points. In access point policies, S3 policy actions for bucket operations require you to use the access point ARN for the Resource element in the following format.

"Resource": "arn:aws:s3:us-west-2:123456789012:accesspoint/example-access-point"

The following access point policy grants the user Akua with account 12345678901 the s3:ListBucket permission to perform the ListObjectsV2 API operation through the S3 access point named example-access-point. This permission allows Akua to list the objects in the bucket that's associated with example-access-point.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "Allow Akua to list objects in the bucket through access point",
            "Effect": "Allow",
            "Principal": {
                "AWS": "arn:aws:iam::12345678901:user/Akua"
            },
            "Action": [
            "s3:ListBucket"
            ],
            "Resource": "arn:aws:s3:us-west-2:123456789012:accesspoint/example-access-point"
        }
    ]
}

Object operations

Object operations are S3 API operations that act upon the object resource type. For example, GetObject, PutObject, and DeleteObject. S3 policy actions for object operations require the Resource element in policies to be the S3 object ARN in the following example formats.

"Resource": "arn:aws:s3:::amzn-s3-demo-bucket/*"

"Resource": "arn:aws:s3:::amzn-s3-demo-bucket/prefix/*"

The following bucket policy grants the user Akua with account 12345678901 the s3:PutObject permission. This permission allows Akua to use the PutObject API operation to upload objects to the S3 bucket named amzn-s3-demo-bucket.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "Allow Akua to upload objects",
            "Effect": "Allow",
            "Principal": {
                "AWS": "arn:aws:iam::12345678901:user/Akua"
            },
            "Action": [
            "s3:PutObject"
            ],
            "Resource": "arn:aws:s3:::amzn-s3-demo-bucket/*"
        }
    ]
}

Object operations in access point policies

When you use S3 Access Points to control access to object operations, you can use access point policies. When you use access point policies, S3 policy actions for object operations require you to use the access point ARN for the Resource element in the following format: arn:aws:s3:region:account-id:accesspoint/access-point-name/object/resource. For object operations that use access points, you must include the /object/ value after the whole access point ARN in the Resource element. Here are some examples.

"Resource": "arn:aws:s3:us-west-2:123456789012:accesspoint/example-access-point/object/*"

"Resource": "arn:aws:s3:us-west-2:123456789012:accesspoint/example-access-point/object/prefix/*"

The following access point policy grants the user Akua with account 12345678901 the s3:GetObject permission. This permission allows Akua to perform the GetObject API operation through the access point named example-access-point on all objects in the bucket that's associated with the access point.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "Allow Akua to get objects through access point",
            "Effect": "Allow",
            "Principal": {
                "AWS": "arn:aws:iam::12345678901:user/Akua"
            },
            "Action": [
            "s3:GetObject"
            ],
            "Resource": "arn:aws:s3:us-west-2:123456789012:accesspoint/example-access-point/object/*"
        }
    ]
}

Access point operations

Access point operations are S3 API operations that operate on the accesspoint resource type. For example, CreateAccessPoint, DeleteAccessPoint, and GetAccessPointPolicy. S3 policy actions for access point operations can only be used in IAM identity-based policies, not in bucket policies or access point policies. Access points operations require the Resource element to be the access point ARN in the following example format.

"Resource": "arn:aws:s3:us-west-2:123456789012:accesspoint/example-access-point"

The following IAM identity-based policy grants the s3:GetAccessPointPolicy permission to perform the GetAccessPointPolicy API operation on the S3 access point named example-access-point.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "Grant permission to retrieve the access point policy of access point example-access-point",
            "Effect": "Allow",
            "Action": [
            "s3:GetAccessPointPolicy"
            ],
            "Resource": "arn:aws:s3:*:123456789012:accesspoint/example-access-point"
        }
    ]
}

When you use Access Points, to control access to bucket operations, see Bucket operations in access point policies; to control access to object operations, see Object operations in access point policies. For more information about how to configure access point policies, see Configuring IAM policies for using access points.

Object Lambda Access Point operations

With Amazon S3 Object Lambda, you can add your own code to Amazon S3 GET, LIST, and HEAD requests to modify and process data as it is returned to an application. You can make requests through an Object Lambda Access Point, which works the same as making requests through other access points. For more information, see Transforming objects with S3 Object Lambda.

For more information about how to configure policies for Object Lambda Access Point operations, see Configuring IAM policies for Object Lambda Access Points.

Multi-Region Access Point operations

A Multi-Region Access Point provides a global endpoint that applications can use to fulfill requests from S3 buckets that are located in multiple AWS Region. You can use a Multi-Region Access Point to build multi-Region applications with the same architecture that's used in a single Region, and then run those applications anywhere in the world. For more information, see Managing multi-Region traffic with Multi-Region Access Points.

For more information about how to configure policies for Multi-Region Access Point operations, see Multi-Region Access Point policy examples.

Batch job operations

(Batch Operations) job operations are S3 API operations that operate on the job resource type. For example, DescribeJob and CreateJob. S3 policy actions for job operations can only be used in IAM identity-based policies, not in bucket policies. Also, job operations require the Resource element in IAM identity-based policies to be the job ARN in the following example format.

"Resource": "arn:aws:s3:*:123456789012:job/*"

The following IAM identity-based policy grants the s3:DescribeJob permission to perform the DescribeJob API operation on the S3 Batch Operations job named example-job.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "Allow describing the Batch operation job example-job",
            "Effect": "Allow",
            "Action": [
            "s3:DescribeJob"
            ],
            "Resource": "arn:aws:s3:*:123456789012:job/example-job"
        }
    ]
}

S3 Storage Lens configuration operations

For more information about how to configure S3 Storage Lens configuration operations, see Setting Amazon S3 Storage Lens permissions.

Account operations

Account operations are S3 API operations that operate on the account level. For example, GetPublicAccessBlock (for account). Account isn't a resource type defined by Amazon S3. S3 policy actions for account operations can only be used in IAM identity-based policies, not in bucket policies. Also, account operations require the Resource element in IAM identity-based policies to be "*".

The following IAM identity-based policy grants the s3:GetAccountPublicAccessBlock permission to perform the account-level GetPublicAccessBlock API operation and retrieve the account-level Public Access Block settings.

{
   "Version":"2012-10-17",
   "Statement":[
      {
         "Sid":"Allow retrieving the account-level Public Access Block settings",
         "Effect":"Allow",
         "Action":[
            "s3:GetAccountPublicAccessBlock" 
         ],
         "Resource":[
            "*"
         ]
       }
    ]
}

Policy examples for Amazon S3

Policy resources for Amazon S3

Supports policy resources: Yes

Administrators can use AWS JSON policies to specify who has access to what. That is, which principal can perform actions on what resources, and under what conditions.

The Resource JSON policy element specifies the object or objects to which the action applies. Statements must include either a Resource or a NotResource element. As a best practice, specify a resource using its Amazon Resource Name (ARN). You can do this for actions that support a specific resource type, known as resource-level permissions.

For actions that don't support resource-level permissions, such as listing operations, use a wildcard (*) to indicate that the statement applies to all resources.

"Resource": "*"

Some Amazon S3 API actions support multiple resources. For example, s3:GetObject accesses example-resource-1 and example-resource-2, so a principal must have permissions to access both resources. To specify multiple resources in a single statement, separate the ARNs with commas, as shown in the following example.

"Resource": [
      "example-resource-1",
      "example-resource-2"

Resources in Amazon S3 are buckets, objects, access points, or jobs. In a policy, use the Amazon Resource Name (ARN) of the bucket, object, access point, or job to identify the resource.

To see a complete list of Amazon S3 resource types and their ARNs, see Resources defined by Amazon S3 in the Service Authorization Reference. To learn with which actions you can specify the ARN of each resource, see Actions defined by Amazon S3.

For more information about the permissions to S3 API operations by S3 resource types, see Required permissions for Amazon S3 API operations.

Wildcard characters in resource ARNs

You can use wildcard characters as part of the resource ARN. You can use the wildcard characters (* and ?) within any ARN segment (the parts separated by colons). An asterisk (*) represents any combination of zero or more characters, and a question mark (?) represents any single character. You can use multiple * or ? characters in each segment. However, a wildcard character can't span segments.

Policy variables for resource ARNs

You can use policy variables in Amazon S3 ARNs. At policy-evaluation time, these predefined variables are replaced by their corresponding values. Suppose that you organize your bucket as a collection of folders, with one folder for each of your users. The folder name is the same as the username. To grant users permission to their folders, you can specify a policy variable in the resource ARN:

arn:aws:s3:::bucket_name/developers/${aws:username}/

At runtime, when the policy is evaluated, the variable ${aws:username} in the resource ARN is substituted with the username of the person who is making the request.

Policy examples for Amazon S3

Policy condition keys for Amazon S3

Supports service-specific policy condition keys: Yes

Administrators can use AWS JSON policies to specify who has access to what. That is, which principal can perform actions on what resources, and under what conditions.

The Condition element (or Condition block) lets you specify conditions in which a statement is in effect. The Condition element is optional. You can create conditional expressions that use condition operators, such as equals or less than, to match the condition in the policy with values in the request.

If you specify multiple Condition elements in a statement, or multiple keys in a single Condition element, AWS evaluates them using a logical AND operation. If you specify multiple values for a single condition key, AWS evaluates the condition using a logical OR operation. All of the conditions must be met before the statement's permissions are granted.

You can also use placeholder variables when you specify conditions. For example, you can grant an IAM user permission to access a resource only if it is tagged with their IAM user name. For more information, see IAM policy elements: variables and tags in the IAM User Guide.

AWS supports global condition keys and service-specific condition keys. To see all AWS global condition keys, see AWS global condition context keys in the IAM User Guide.

Each Amazon S3 condition key maps to the same name request header allowed by the API on which the condition can be set. Amazon S3‐specific condition keys dictate the behavior of the same name request headers. For example, the condition key s3:VersionId used to grant conditional permission for the s3:GetObjectVersion permission defines behavior of the versionId query parameter that you set in a GET Object request.

To see a list of Amazon S3 condition keys, see Condition keys for Amazon S3 in the Service Authorization Reference. To learn with which actions and resources you can use a condition key, see Actions defined by Amazon S3.

Example: Restricting object uploads to objects with a specific storage class

Suppose that Account A, represented by account ID 123456789012, owns a bucket. The Account A administrator wants to restrict Dave, a user in Account A, so that Dave can upload objects to the bucket only if the object is stored in the STANDARD_IA storage class. To restrict object uploads to a specific storage class, the Account A administrator can use the s3:x-amz-storage-class condition key, as shown in the following example bucket policy.

{
                 "Version": "2012-10-17",
                 "Statement": [
                   {
                     "Sid": "statement1",
                     "Effect": "Allow",
                     "Principal": {
                       "AWS": "arn:aws:iam::123456789012:user/Dave"
                     },
                     "Action": "s3:PutObject",
                     "Resource": "arn:aws:s3:::amzn-s3-demo-bucket1/*",
                     "Condition": {
                       "StringEquals": {
                         "s3:x-amz-storage-class": [
                           "STANDARD_IA"
                         ]
                       }
                     }
                   }
                 ]
            }

In the example, the Condition block specifies the StringEquals condition that is applied to the specified key-value pair, "s3:x-amz-acl":["public-read"]. There is a set of predefined keys that you can use in expressing a condition. The example uses the s3:x-amz-acl condition key. This condition requires the user to include the x-amz-acl header with value public-read in every PutObject request.

Policy examples for Amazon S3

ACLs in Amazon S3

Supports ACLs: Yes

In Amazon S3, access control lists (ACLs) control which AWS accounts have permissions to access a resource. ACLs are similar to resource-based policies, although they do not use the JSON policy document format.

For information about using ACLs to control access in Amazon S3, see Managing access with ACLs.

ABAC with Amazon S3

Supports ABAC (tags in policies): Partial

Attribute-based access control (ABAC) is an authorization strategy that defines permissions based on attributes. In AWS, these attributes are called tags. You can attach tags to IAM entities (users or roles) and to many AWS resources. Tagging entities and resources is the first step of ABAC. Then you design ABAC policies to allow operations when the principal's tag matches the tag on the resource that they are trying to access.

ABAC is helpful in environments that are growing rapidly and helps with situations where policy management becomes cumbersome.

To control access based on tags, you provide tag information in the condition element of a policy using the aws:ResourceTag/key-name, aws:RequestTag/key-name, or aws:TagKeys condition keys.

If a service supports all three condition keys for every resource type, then the value is Yes for the service. If a service supports all three condition keys for only some resource types, then the value is Partial.

For more information about ABAC, see Define permissions with ABAC authorization in the IAM User Guide. To view a tutorial with steps for setting up ABAC, see Use attribute-based access control (ABAC) in the IAM User Guide.

To view example identity-based policies for limiting access to S3 Batch Operations jobs based on tags, see Controlling permissions for Batch Operations using job tags.

ABAC and object tags

In ABAC policies, objects use s3: tags instead of aws: tags. To control access to objects based on object tags, you provide tag information in the Condition element of a policy using the following tags:

For information about using object tags to control access, including example permission policies, see Tagging and access control policies.

Using temporary credentials with Amazon S3

Supports temporary credentials: Yes

Some AWS services don't work when you sign in using temporary credentials. For additional information, including which AWS services work with temporary credentials, see AWS services that work with IAM in the IAM User Guide.

You are using temporary credentials if you sign in to the AWS Management Console using any method except a user name and password. For example, when you access AWS using your company's single sign-on (SSO) link, that process automatically creates temporary credentials. You also automatically create temporary credentials when you sign in to the console as a user and then switch roles. For more information about switching roles, see Switch from a user to an IAM role (console) in the IAM User Guide.

You can manually create temporary credentials using the AWS CLI or AWS API. You can then use those temporary credentials to access AWS. AWS recommends that you dynamically generate temporary credentials instead of using long-term access keys. For more information, see Temporary security credentials in IAM.

Forward access sessions for Amazon S3

Supports forward access sessions (FAS): Yes

When you use an IAM user or role to perform actions in AWS, you are considered a principal. When you use some services, you might perform an action that then initiates another action in a different service. FAS uses the permissions of the principal calling an AWS service, combined with the requesting AWS service to make requests to downstream services. FAS requests are only made when a service receives a request that requires interactions with other AWS services or resources to complete. In this case, you must have permissions to perform both actions. For policy details when making FAS requests, see Forward access sessions.

Service roles for Amazon S3

Supports service roles: Yes

A service role is an IAM role that a service assumes to perform actions on your behalf. An IAM administrator can create, modify, and delete a service role from within IAM. For more information, see Create a role to delegate permissions to an AWS service in the IAM User Guide.

Service-linked roles for Amazon S3

Supports service-linked roles: Partial

A service-linked role is a type of service role that is linked to an AWS service. The service can assume the role to perform an action on your behalf. Service-linked roles appear in your AWS account and are owned by the service. An IAM administrator can view, but not edit the permissions for service-linked roles.

Amazon S3 supports service-linked roles for Amazon S3 Storage Lens. For details about creating or managing Amazon S3 service-linked roles, see Using service-linked roles for Amazon S3 Storage Lens.

Amazon S3 Service as a Principal