Restricting access to Parameter Store parameters using IAM policies

You restrict access to AWS Systems Manager parameters by using AWS Identity and Access Management (IAM). More specifically, you create IAM policies that restrict access to the following API operations:

When using IAM policies to restrict access to Systems Manager parameters, we recommend that you create and use restrictive IAM policies. For example, the following policy allows a user to call the DescribeParameters and GetParameters API operations for a limited set of resources. This means that the user can get information about and use all parameters that begin with prod-*.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "ssm:DescribeParameters"
            ],
            "Resource": "*"
        },
        {
            "Effect": "Allow",
            "Action": [
                "ssm:GetParameters"
            ],
            "Resource": "arn:aws:ssm:us-east-2:123456789012:parameter/prod-*"
        }
    ]
}

For trusted administrators, you can provide access to all Systems Manager parameter API operations by using a policy similar to the following example. This policy gives the user full access to all production parameters that begin with dbserver-prod-*.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "ssm:PutParameter",
                "ssm:DeleteParameter",
                "ssm:GetParameterHistory",
                "ssm:GetParametersByPath",
                "ssm:GetParameters",
                "ssm:GetParameter",
                "ssm:DeleteParameters"
            ],
            "Resource": "arn:aws:ssm:us-east-2:123456789012:parameter/dbserver-prod-*"
        },
        {
            "Effect": "Allow",
            "Action": "ssm:DescribeParameters",
            "Resource": "*"
        }
    ]
}

Denying permissions

Each API is unique and has distinct operations and permissions that you can allow or deny individually. An explicit deny in any policy overrides the allow.

If you want all API operations retrieving parameter values to have the same behavior, then you can use a pattern like GetParameter* in a policy. The following example shows how to deny GetParameter, GetParameters, GetParameterHistory, and GetParametersByPath for all parameters beginning with prod-*.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Deny",
            "Action": [
                "ssm:GetParameter*"
            ],
            "Resource": "arn:aws:ssm:us-east-2:123456789012:parameter/prod-*"
        }
    ]
}

The following example shows how to deny some commands while allowing the user to perform other commands on all parameters that begin with prod-*.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Deny",
            "Action": [
                "ssm:PutParameter",
                "ssm:DeleteParameter",
                "ssm:DeleteParameters",
                "ssm:DescribeParameters"
            ],
            "Resource": "*"
        },
        {
            "Effect": "Allow",
            "Action": [
                "ssm:GetParametersByPath",
                "ssm:GetParameters",
                "ssm:GetParameter",
                "ssm:GetParameterHistory"
            ],
            "Resource": "arn:aws:ssm:us-east-2:123456789012:parameter/prod-*"
        }
    ]
}

Allowing only specific parameters to run on nodes

You can control access so that managed nodes can run only parameters that you specify.

If you choose the SecureString parameter type when you create your parameter, Systems Manager uses AWS KMS to encrypt the parameter value. AWS KMS encrypts the value by using either an AWS managed key or a customer managed key. For more information about AWS KMS and AWS KMS key, see the AWS Key Management Service Developer Guide.

You can view the AWS managed key by running the following command from the AWS CLI.

aws kms describe-key --key-id alias/aws/ssm

The following example allows nodes to get a parameter value only for parameters that begin with prod-. If the parameter is a SecureString parameter, then the node decrypts the string using AWS KMS.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "ssm:GetParameters"
            ],
            "Resource": [
                "arn:aws:ssm:us-east-2:123456789012:parameter/prod-*"
            ]
        },
        {
            "Effect": "Allow",
            "Action": [
                "kms:Decrypt"
            ],
            "Resource": [
                "arn:aws:kms:us-east-2:123456789012:key/4914ec06-e888-4ea5-a371-5b88eEXAMPLE"
            ]
        }
    ]
}

IAM permissions for using AWS default keys and customer managed keys

Parameter Store SecureString parameters are encrypted and decrypted using AWS KMS keys. You can choose to encrypt your SecureString parameters using either an AWS KMS key or the default KMS key provided by AWS.

When using a customer managed key, the IAM policy that grants a user access to a parameter or parameter path must provide explicit kms:Encrypt permissions for the key. For example, the following policy allows a user to create, update, and view SecureString parameters that begin with prod- in the specified AWS Region and AWS account.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "ssm:PutParameter",
                "ssm:GetParameter",
                "ssm:GetParameters"
            ],
            "Resource": [
                "arn:aws:ssm:us-east-2:111122223333:parameter/prod-*"
            ]
        },
        {
            "Effect": "Allow",
            "Action": [
                "kms:Decrypt",
                "kms:Encrypt",
                "kms:GenerateDataKey"  
            ],
            "Resource": [
                "arn:aws:kms:us-east-2:111122223333:key/1234abcd-12ab-34cd-56ef-12345EXAMPLE"
            ]
        }
    ]
}

¹The kms:GenerateDataKey permission is required for creating encrypted advanced parameters using the specified customer managed key.

By contrast, all users within the customer account have access to the default AWS managed key. If you use this default key to encrypt SecureString parameters and don't want users to work with SecureString parameters, their IAM policies must explicitly deny access to the default key, as demonstrated in the following policy example.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Deny",
            "Action": [
                "kms:Decrypt",
                "kms:GenerateDataKey"
            ],
            "Resource": [
                "arn:aws:kms:us-east-2:111122223333:key/abcd1234-ab12-cd34-ef56-abcdeEXAMPLE"
            ]
        }
    ]
}

If you require fine-grained access control over the SecureString parameters in your account, you should use a customer managed key to protect and restrict access to these parameters. We also recommend using AWS CloudTrail to monitor SecureString parameter activities.

For more information, see the following topics: