aws_s3_bucket

Use the aws_s3_bucket InSpec audit resource to test properties of a single AWS bucket.

To test properties of a multiple S3 buckets, use the aws_s3_buckets resource.


Limitations

S3 bucket security is a complex matter. For details on how AWS evaluates requests for access, please see the AWS documentation. S3 buckets and the objects they contain support three different types of access control: bucket ACLs, bucket policies, and object ACLs.

As of January 2018, this resource supports evaluating bucket ACLs and bucket policies. We do not support evaluating object ACLs because it introduces scalability concerns in the AWS API; we recommend using AWS mechanisms such as CloudTrail and Config to detect insecure object ACLs.

In particular, users of the be_public matcher should carefully examine the conditions under which the matcher will detect an insecure bucket. See the be_public section under the Matchers section below.


Syntax

An aws_s3_bucket resource block declares a bucket by name, and then lists tests to be performed.

describe aws_s3_bucket(bucket_name: 'test_bucket') do
  it { should exist }
  it { should_not be_public }
end

describe aws_s3_bucket('test_bucket') do
  it { should exist }
end


Examples

The following examples show how to use this InSpec audit resource.

Test the bucket-level ACL

describe aws_s3_bucket('test_bucket') do
  its('bucket_acl.count') { should eq 1 }
end

Check if a bucket has a bucket policy

describe aws_s3_bucket('test_bucket') do
  its('bucket_policy') { should be_empty }
end

Check if a bucket appears to be exposed to the public

# See Limitations section above
describe aws_s3_bucket('test_bucket') do
  it { should_not be_public }
end


Properties

region

The region property identifies the AWS Region in which the S3 bucket is located.

describe aws_s3_bucket('test_bucket') do
  # Check if the correct region is set
  its('region') { should eq 'us-east-1' }
end

Unsupported Properties

bucket_acl

The bucket_acl property is a low-level property that lists the individual Bucket ACL grants in effect on the bucket. Other higher-level properties, such as be_public, are more concise and easier to use. You can use the bucket_acl property to investigate which grants are in effect, causing be_public to fail.

The value of bucket_acl is an array of simple objects. Each object has a permission property and a grantee property. The permission property will be a string such as ‘READ’, ‘WRITE’ etc (See the AWS documentation for a full list). The grantee property contains sub-properties, such as type and uri.

bucket_acl = aws_s3_bucket('my-bucket')

# Look for grants to "AllUsers" (that is, the public)
all_users_grants = bucket_acl.select do |g|
  g.grantee.type == 'Group' && g.grantee.uri =~ /AllUsers/
end

# Look for grants to "AuthenticatedUsers" (that is, any authenticated AWS user - nearly public)
auth_grants = bucket_acl.select do |g|
  g.grantee.type == 'Group' && g.grantee.uri =~ /AuthenticatedUsers/
end

bucket_policy

The bucket_policy is a low-level property that describes the IAM policy document controlling access to the bucket. The bucket_policy property returns a Ruby structure that you can probe to check for particular statements. We recommend using a higher-level property, such as be_public, which is concise and easier to implement in your policy files.

The bucket_policy property returns an array of simple objects, each object being an IAM Policy Statement. See the AWS documentation for details about the structure of this data.

If there is no bucket policy, this property returns an empty array.

bucket_policy = aws_s3_bucket('my-bucket')

# Look for statements that allow the general public to do things
# This may be a false positive; it is possible these statements
# could be protected by conditions, such as IP restrictions.
public_statements = bucket_policy.select do |s|
  s.effect == 'Allow' && s.principal == '*'
end


Matchers

This InSpec audit resource has the following special matchers. For a full list of available matchers, please visit our matchers page.

be_public

The be_public matcher tests if the bucket has potentially insecure access controls. This high-level matcher detects several insecure conditions, which may be enhanced in the future. Currently, the matcher reports an insecure bucket if any of the following conditions are met:

  1. A bucket ACL grant exists for the ‘AllUsers’ group
  2. A bucket ACL grant exists for the ‘AuthenticatedUsers’ group
  3. A bucket policy has an effect ‘Allow’ and principal ‘*’

Note: This resource does not detect insecure object ACLs.

it { should_not be_public }

have_access_logging_enabled

The have_access_logging_enabled matcher tests if access logging is enabled for the s3 bucket.

it { should have_access_logging_enabled }