Basic Amazon IoT Core policy variables

Amazon IoT Core defines the following basic policy variables:

The following Amazon IoT Core policy shows a policy that uses policy variables. aws:SourceIp can be used in the Condition element of your policy to allow principals to make API requests only within a specific address range. For examples, see Authorizing users and cloud services to use Amazon IoT Jobs.

{
	"Version": "2012-10-17",
	"Statement": [
		{
			"Effect": "Allow",
			"Action": [
				"iot:Connect"
			],
			"Resource": [
				"arn:aws:iot:us-east-1:123456789012:client/clientid1"
			]
		},
		{
			"Effect": "Allow",
			"Action": [
				"iot:Publish"
			],
			"Resource": [
				"arn:aws:iot:us-east-1:123456789012:topic/my/topic/${iot:ClientId}"
			],
			"Condition": {
				"IpAddress": {
					"aws:SourceIp": "123.45.167.89"
				}
			}
		}
	]
}

In these examples, ${iot:ClientId} is replaced by the ID of the client connected to the Amazon IoT Core message broker when the policy is evaluated. When you use policy variables like ${iot:ClientId}, you can inadvertently open access to unintended topics. For example, if you use a policy that uses ${iot:ClientId} to specify a topic filter:

{
    "Effect": "Allow",
    "Action": ["iot:Subscribe"],
    "Resource": [
      "arn:aws:iot:us-east-1:123456789012:topicfilter/my/${iot:ClientId}/topic"
    ]
}

A client can connect using + as the client ID. This would allow the user to subscribe to any topic that matches the topic filter my/+/topic. To protect against such security gaps, use the iot:Connect policy action to control which client IDs can connect. For example, this policy allows only those clients whose client ID is clientid1 to connect:

{
    "Version": "2012-10-17",
    "Statement": [
      {
        "Effect": "Allow",
        "Action": ["iot:Connect"],
        "Resource": [
          "arn:aws:iot:us-east-1:123456789012:client/clientid1"
        ]
      }
    ]
}