Access control list (ACL) overview - Amazon Simple Storage Service

Access control list (ACL) overview

Amazon S3 access control lists (ACLs) enable you to manage access to buckets and objects. Each bucket and object has an ACL attached to it as a subresource. It defines which AWS accounts or groups are granted access and the type of access. When a request is received against a resource, Amazon S3 checks the corresponding ACL to verify that the requester has the necessary access permissions.

S3 Object Ownership is an Amazon S3 bucket-level setting that you can use to both control ownership of the objects that are uploaded to your bucket and to disable or enable ACLs. By default, Object Ownership is set to the Bucket owner enforced setting, and all ACLs are disabled. When ACLs are disabled, the bucket owner owns all the objects in the bucket and manages access to them exclusively by using access-management policies.

A majority of modern use cases in Amazon S3 no longer require the use of ACLs. We recommend that you keep ACLs disabled, except in unusual circumstances where you need to control access for each object individually. With ACLs disabled, you can use policies to control access to all objects in your bucket, regardless of who uploaded the objects to your bucket. For more information, see Controlling ownership of objects and disabling ACLs for your bucket.

Important

If your bucket uses the Bucket owner enforced setting for S3 Object Ownership, you must use policies to grant access to your bucket and the objects in it. With the Bucket owner enforced setting enabled, requests to set access control lists (ACLs) or update ACLs fail and return the AccessControlListNotSupported error code. Requests to read ACLs are still supported.

When you create a bucket or an object, Amazon S3 creates a default ACL that grants the resource owner full control over the resource. This is shown in the following sample bucket ACL (the default object ACL has the same structure):

<?xml version="1.0" encoding="UTF-8"?> <AccessControlPolicy xmlns="http://s3.amazonaws.com/doc/2006-03-01/"> <Owner> <ID>*** Owner-Canonical-User-ID ***</ID> <DisplayName>owner-display-name</DisplayName> </Owner> <AccessControlList> <Grant> <Grantee xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="Canonical User"> <ID>*** Owner-Canonical-User-ID ***</ID> <DisplayName>display-name</DisplayName> </Grantee> <Permission>FULL_CONTROL</Permission> </Grant> </AccessControlList> </AccessControlPolicy>

The sample ACL includes an Owner element that identifies the owner by the AWS account's canonical user ID. For instructions on finding your canonical user ID, see Finding an AWS account canonical user ID. The Grant element identifies the grantee (either an AWS account or a predefined group) and the permission granted. This default ACL has one Grant element for the owner. You grant permissions by adding Grant elements, with each grant identifying the grantee and the permission.

Note

An ACL can have up to 100 grants.

Who is a grantee?

A grantee can be an AWS account or one of the predefined Amazon S3 groups. You grant permission to an AWS account using the email address or the canonical user ID. However, if you provide an email address in your grant request, Amazon S3 finds the canonical user ID for that account and adds it to the ACL. The resulting ACLs always contain the canonical user ID for the AWS account, not the email address of the AWS account.

When you grant access rights, you specify each grantee as a type="value" pair, where type is one of the following:

  • id – If the value specified is the canonical user ID of an AWS account

  • uri – If you are granting permissions to a predefined group

  • emailAddress – If the value specified is the email address of an AWS account

Important

Using email addresses to specify a grantee is only supported in the following AWS Regions:

  • US East (N. Virginia)

  • US West (N. California)

  • US West (Oregon)

  • Asia Pacific (Singapore)

  • Asia Pacific (Sydney)

  • Asia Pacific (Tokyo)

  • Europe (Ireland)

  • South America (São Paulo)

For a list of all the Amazon S3 supported regions and endpoints, see Regions and Endpoints in the Amazon Web Services General Reference.

Example: Email address

For example, the following x-amz-grant-read header grants the AWS accounts identified by email addresses permissions to read object data and its metadata:

x-amz-grant-read: emailAddress="xyz@example.com", emailAddress="abc@example.com"
Warning

When you grant other AWS accounts access to your resources, be aware that the AWS accounts can delegate their permissions to users under their accounts. This is known as cross-account access. For information about using cross-account access, see Creating a Role to Delegate Permissions to an IAM User in the IAM User Guide.

Finding an AWS account canonical user ID

The canonical user ID is associated with your AWS account. This ID is a long string of characters, such as:

79a59df900b949e55d96a1e698fbacedfd6e09d98eacf8f8d5218e7cd47ef2be

For information about how to find the canonical user ID for your account, see Find the canonical user ID for your AWS account in the AWS Account Management Reference Guide.

You can also look up the canonical user ID of an AWS account by reading the ACL of a bucket or an object to which the AWS account has access permissions. When an individual AWS account is granted permissions by a grant request, a grant entry is added to the ACL with the account's canonical user ID.

Note

If you make your bucket public (not recommended), any unauthenticated user can upload objects to the bucket. These anonymous users don't have an AWS account. When an anonymous user uploads an object to your bucket, Amazon S3 adds a special canonical user ID (65a011a29cdf8ec533ec3d1ccaae921c) as the object owner in the ACL. For more information, see Amazon S3 bucket and object ownership.

Amazon S3 predefined groups

Amazon S3 has a set of predefined groups. When granting account access to a group, you specify one of the Amazon S3 URIs instead of a canonical user ID. Amazon S3 provides the following predefined groups:

  • Authenticated Users group – Represented by http://acs.amazonaws.com/groups/global/AuthenticatedUsers.

    This group represents all AWS accounts. Access permission to this group allows any AWS account to access the resource. However, all requests must be signed (authenticated).

    Warning

    When you grant access to the Authenticated Users group, any AWS authenticated user in the world can access your resource.

  • All Users group – Represented by http://acs.amazonaws.com/groups/global/AllUsers.

    Access permission to this group allows anyone in the world access to the resource. The requests can be signed (authenticated) or unsigned (anonymous). Unsigned requests omit the Authentication header in the request.

    Warning

    We highly recommend that you never grant the All Users group WRITE, WRITE_ACP, or FULL_CONTROL permissions. For example, while WRITE permissions do not allow non-owners to overwrite or delete existing objects, WRITE permissions still allow anyone to store objects in your bucket, for which you are billed. For more details about these permissions, see the following section What permissions can I grant?.

  • Log Delivery group – Represented by http://acs.amazonaws.com/groups/s3/LogDelivery.

    WRITE permission on a bucket enables this group to write server access logs (see Logging requests with server access logging) to the bucket.

Note

When using ACLs, a grantee can be an AWS account or one of the predefined Amazon S3 groups. However, the grantee cannot be an IAM user. For more information about AWS users and permissions within IAM, see Using AWS Identity and Access Management.

What permissions can I grant?

The following table lists the set of permissions that Amazon S3 supports in an ACL. The set of ACL permissions is the same for an object ACL and a bucket ACL. However, depending on the context (bucket ACL or object ACL), these ACL permissions grant permissions for specific buckets or object operations. The table lists the permissions and describes what they mean in the context of objects and buckets.

For more information about ACL permissions in the Amazon S3 console, see Configuring ACLs.

Permission When granted on a bucket When granted on an object
READ Allows grantee to list the objects in the bucket Allows grantee to read the object data and its metadata
WRITE Allows grantee to create new objects in the bucket. For the bucket and object owners of existing objects, also allows deletions and overwrites of those objects Not applicable
READ_ACP Allows grantee to read the bucket ACL Allows grantee to read the object ACL
WRITE_ACP Allows grantee to write the ACL for the applicable bucket Allows grantee to write the ACL for the applicable object
FULL_CONTROL Allows grantee the READ, WRITE, READ_ACP, and WRITE_ACP permissions on the bucket Allows grantee the READ, READ_ACP, and WRITE_ACP permissions on the object
Warning

Use caution when granting access permissions to your S3 buckets and objects. For example, granting WRITE access to a bucket allows the grantee to create objects in the bucket. We highly recommend that you read through the entire Access control list (ACL) overview section before granting permissions.

Mapping of ACL permissions and access policy permissions

As shown in the preceding table, an ACL allows only a finite set of permissions, compared to the number of permissions that you can set in an access policy (see Policy actions for Amazon S3). Each of these permissions allows one or more Amazon S3 operations.

The following table shows how each ACL permission maps to the corresponding access policy permissions. As you can see, access policy allows more permissions than an ACL does. You use ACLs primarily to grant basic read/write permissions, similar to file system permissions. For more information about when to use an ACL, see Identity and Access Management for Amazon S3.

For more information about ACL permissions in the Amazon S3 console, see Configuring ACLs.

ACL permission Corresponding access policy permissions when the ACL permission is granted on a bucket Corresponding access policy permissions when the ACL permission is granted on an object
READ s3:ListBucket, s3:ListBucketVersions, and s3:ListBucketMultipartUploads s3:GetObject and s3:GetObjectVersion
WRITE

s3:PutObject

Bucket owner can create, overwrite, and delete any object in the bucket, and object owner has FULL_CONTROL over their object.

In addition, when the grantee is the bucket owner, granting WRITE permission in a bucket ACL allows the s3:DeleteObjectVersion action to be performed on any version in that bucket.

Not applicable
READ_ACP s3:GetBucketAcl s3:GetObjectAcl and s3:GetObjectVersionAcl
WRITE_ACP s3:PutBucketAcl s3:PutObjectAcl and s3:PutObjectVersionAcl
FULL_CONTROL Equivalent to granting READ, WRITE, READ_ACP, and WRITE_ACP ACL permissions. Accordingly, this ACL permission maps to a combination of corresponding access policy permissions. Equivalent to granting READ, READ_ACP, and WRITE_ACP ACL permissions. Accordingly, this ACL permission maps to a combination of corresponding access policy permissions.

Condition keys

When you grant access policy permissions, you can use condition keys to constrain the value for the ACL on an object using a bucket policy. The following context keys correspond to ACLs. You can use these context keys to mandate the use of a specific ACL in a request:

  • s3:x-amz-grant-read ‐ Require read access.

  • s3:x-amz-grant-write ‐ Require write access.

  • s3:x-amz-grant-read-acp ‐ Require read access to the bucket ACL.

  • s3:x-amz-grant-write-acp ‐ Require write access to the bucket ACL.

  • s3:x-amz-grant-full-control ‐ Require full control.

  • s3:x-amz-acl ‐ Require a Canned ACL.

For example policies that involve ACL-specific headers, see Granting s3:PutObject permission with a condition requiring the bucket owner to get full control. For a complete list of Amazon S3 specific condition keys, see Actions, resources, and condition keys for Amazon S3 in the Service Authorization Reference.

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

aclRequired values for common Amazon S3 requests

To identify Amazon S3 requests that required ACLs for authorization, you can use the aclRequired value in Amazon S3 server access logs or AWS CloudTrail. The aclRequired value that appears in CloudTrail or Amazon S3 server access logs depends on which operations were called and certain information about the requester, object owner, and bucket owner. If no ACLs were required, or if you are setting the bucket-owner-full-control canned ACL, or if the requests are allowed by your bucket policy, the aclRequired value string is "-" in Amazon S3 server access logs and is absent in CloudTrail.

The following tables list the expected aclRequired values in CloudTrail or Amazon S3 server access logs for the various Amazon S3 API operations. You can use this information to understand which Amazon S3 operations depend on ACLs for authorization. In the following tables, A, B, and C represent the different accounts associated with the requester, object owner, and bucket owner. Entries with an asterisk (*) indicate any of accounts A, B, or C.

Note

PutObject operations in the following table, unless specified otherwise, indicate requests that do not set an ACL, unless the ACL is a bucket-owner-full-control ACL. A null value for aclRequired indicates that aclRequired is absent in AWS CloudTrail logs.

The following table shows the aclRequired values for CloudTrail.

Operation name Requester Object owner Bucket owner Bucket policy grants access aclRequired value Reason
GetObject A A A Yes or No null Same-account access
A B A Yes or No null Same-account access with bucket owner enforced
A A B Yes null Cross-account access granted by bucket policy
A A B No Yes Cross-account access relies on ACL
A A B Yes null Cross-account access granted by bucket policy
A B B No Yes Cross-account access relies on ACL
A B C Yes null Cross-account access granted by bucket policy
A B C No Yes Cross-account access relies on ACL
PutObject A Not applicable A Yes or No null Same-account access
A Not applicable B Yes null Cross-account access granted by bucket policy
A Not applicable B No Yes Cross-account access relies on ACL
PutObject with an ACL (except for bucket-owner-full-control) * Not applicable * Yes or No Yes Request grants ACL
ListObjects A Not applicable A Yes or No null Same-account access
A Not applicable B Yes null Cross-account access granted by bucket policy
A Not applicable B No Yes Cross-account access relies on ACL
DeleteObject A Not applicable A Yes or No null Same-account access
A Not applicable B Yes null Cross-account access granted by bucket policy
A Not applicable B No Yes Cross-account access relies on ACL
PutObjectAcl * * * Yes or No Yes Request grants ACL
PutBucketAcl * Not applicable * Yes or No Yes Request grants ACL

Note

REST.PUT.OBJECT operations in the following table, unless specified otherwise, indicate requests that do not set an ACL, unless the ACL is a bucket-owner-full-control ACL. An aclRequired value string of "-" indicates a null value in Amazon S3 server access logs.

The following table shows the aclRequired values for Amazon S3 server access logs.

Operation name Requester Object owner Bucket owner Bucket policy grants access aclRequired value Reason
REST.GET.OBJECT A A A Yes or No - Same-account access
A B A Yes or No - Same-account access with bucket owner enforced
A A B Yes - Cross-account access granted by bucket policy
A A B No Yes Cross-account access relies on ACL
A B B Yes - Cross-account access granted by bucket policy
A B B No Yes Cross-account access relies on ACL
A B C Yes - Cross-account access granted by bucket policy
A B C No Yes Cross-account access relies on ACL
REST.PUT.OBJECT A Not applicable A Yes or No - Same-account access
A Not applicable B Yes - Cross-account access granted by bucket policy
A Not applicable B No Yes Cross-account access relies on ACL
REST.PUT.OBJECT with an ACL (except for bucket-owner-full-control) * Not applicable * Yes or No Yes Request grants ACL
REST.GET.BUCKET A Not applicable A Yes or No - Same-account access
A Not applicable B Yes - Cross-account access granted by bucket policy
A Not applicable B No Yes Cross-account access relies on ACL
REST.DELETE.OBJECT A Not applicable A Yes or No - Same-account access
A Not applicable B Yes - Cross-account access granted by bucket policy
A Not applicable B No Yes Cross-account access relies on ACL
REST.PUT.ACL * * * Yes or No Yes Request grants ACL

Sample ACL

The following sample ACL on a bucket identifies the resource owner and a set of grants. The format is the XML representation of an ACL in the Amazon S3 REST API. The bucket owner has FULL_CONTROL of the resource. In addition, the ACL shows how permissions are granted on a resource to two AWS accounts, identified by canonical user ID, and two of the predefined Amazon S3 groups discussed in the preceding section.

<?xml version="1.0" encoding="UTF-8"?> <AccessControlPolicy xmlns="http://s3.amazonaws.com/doc/2006-03-01/"> <Owner> <ID>Owner-canonical-user-ID</ID> <DisplayName>display-name</DisplayName> </Owner> <AccessControlList> <Grant> <Grantee xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="CanonicalUser"> <ID>Owner-canonical-user-ID</ID> <DisplayName>display-name</DisplayName> </Grantee> <Permission>FULL_CONTROL</Permission> </Grant> <Grant> <Grantee xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="CanonicalUser"> <ID>user1-canonical-user-ID</ID> <DisplayName>display-name</DisplayName> </Grantee> <Permission>WRITE</Permission> </Grant> <Grant> <Grantee xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="CanonicalUser"> <ID>user2-canonical-user-ID</ID> <DisplayName>display-name</DisplayName> </Grantee> <Permission>READ</Permission> </Grant> <Grant> <Grantee xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="Group"> <URI>http://acs.amazonaws.com/groups/global/AllUsers</URI> </Grantee> <Permission>READ</Permission> </Grant> <Grant> <Grantee xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="Group"> <URI>http://acs.amazonaws.com/groups/s3/LogDelivery</URI> </Grantee> <Permission>WRITE</Permission> </Grant> </AccessControlList> </AccessControlPolicy>

Canned ACL

Amazon S3 supports a set of predefined grants, known as canned ACLs. Each canned ACL has a predefined set of grantees and permissions. The following table lists the set of canned ACLs and the associated predefined grants.

Canned ACL Applies to Permissions added to ACL
private Bucket and object Owner gets FULL_CONTROL. No one else has access rights (default).
public-read Bucket and object Owner gets FULL_CONTROL. The AllUsers group (see Who is a grantee?) gets READ access.
public-read-write Bucket and object Owner gets FULL_CONTROL. The AllUsers group gets READ and WRITE access. Granting this on a bucket is generally not recommended.
aws-exec-read Bucket and object Owner gets FULL_CONTROL. Amazon EC2 gets READ access to GET an Amazon Machine Image (AMI) bundle from Amazon S3.
authenticated-read Bucket and object Owner gets FULL_CONTROL. The AuthenticatedUsers group gets READ access.
bucket-owner-read Object Object owner gets FULL_CONTROL. Bucket owner gets READ access. If you specify this canned ACL when creating a bucket, Amazon S3 ignores it.
bucket-owner-full-control Object Both the object owner and the bucket owner get FULL_CONTROL over the object. If you specify this canned ACL when creating a bucket, Amazon S3 ignores it.
log-delivery-write Bucket The LogDelivery group gets WRITE and READ_ACP permissions on the bucket. For more information about logs, see (Logging requests with server access logging).
Note

You can specify only one of these canned ACLs in your request.

You specify a canned ACL in your request by using the x-amz-acl request header. When Amazon S3 receives a request with a canned ACL in the request, it adds the predefined grants to the ACL of the resource.