Users, Roles, and Rights

In the AWS cloud, the simplest hierarchy level is that of accounts containing users who are assigned authorizations within the account, such as the ability to create and start VMs or databases. The IAM configuration area is used to manage users or admins.

AWS recommends setting up accounts with sub-accounts. This allows the AWS customer to impose company-wide policies so that even an admin with full rights for a sub-account cannot violate the organizational rules.

When generating an account, AWS also creates the superuser's credentials for this account. By clicking on the user list, the admin will find this superuser. The user has full access to all functions offered by AWS (the exception would be a sub-account with an organizational policy). If the admin creates a second user here, the user is only granted explicitly assigned rights. When creating a new user, you are first prompted for the user name and details of how this user will log on, via CLI/API and/or the Web Console.

Next, the admin assigns rights by selecting from existing user groups (for example S3 Admins, Networkadmins, etc.), assigning roles (S3 Admin, Networkadmin), or as individual assignments at policy level. If you really want to make your life complicated, you can also define an arbitrary combination of these rights for the new user.

To avoid selecting overly liberal permissions by mistake, a permissions boundary can be defined within which, say, the security administrator responsible for AWS restricts permissions in a policy. If a conflict then arises between this limitation and the assigned rights, the limitation wins.

Rights to Resources

AWS controls access through policies. A policy consists of a set of statements, each granting one or more rights to a resource (with wild cards) to a role or user. Optional conditions are possible. Listing 1 shows a section of a policy in JSON format [1].

01 {
02   "Version": "2012-10-17",
03   {
04       "Sid": "s3zugriff",
05       "Effect": "Allow",
06       "Action": [
07         "s3:List*",
08         "s3:Get*"
09       ],
10       "Resource": [
11         "arn:aws:s3:::confidential-data",
12         "arn:aws:s3:::confidential-data/*"
13       ],
14       "Condition": {"Bool": {"aws:MultiFactorAuthPresent": "true"}}
15     }
16   ]
17 }

The Sid field contains a name for the permission, but it is optional. Effect allows or denies access. The Action field contains a list of the API access instances at issue. In the example, these are all listing and downloading operations in the S3 API. The Resource field contains a list of targets for the operations, formulated as Amazon Resource Names (ARNs). The example shows a bucket named confidential-data and its contents. If you do not include the last field Condition, then the rule would be universal.

The condition in line 14 ensures multi-factor authentication of the user for this rule to apply. Depending on the logic to be mapped, the admin either writes individual policies in this form and combines them or bundles several statements into a single policy.

The Right to Interact

Policies are not only used for user access controls, but also to govern the interaction between AWS entities. A lambda function wanting to send a Simple Notification Service (SNS) [2], for example, needs a role that contains a policy with the corresponding rights in the SNS area.

Policies determine which operations are allowed on which objects. The admin assigns them to users or functions. In regard to the CIA triad, a policy controls who can access the data within the created AWS objects. This does not consider the confidentiality and integrity objectives in relation to the AWS administrators.