Developer Guide

Basic Policy Variables

AWS IoT defines the following basic policy variables:

  • iot:ClientId: The client ID used to connect to the AWS IoT message broker.

  • aws:SourceIp: The IP address of the client connected to the AWS IoT message broker.

The following AWS IoT policy shows the use of policy variables:

{ "Version": "2012-10-17", "Statement": [{ "Effect": "Allow", "Action": ["iot:Connect"], "Resource": [ "arn:aws:iot:us-east-1:123451234510:client/${iot:ClientId}" ] }, { "Effect": "Allow", "Action": ["iot:Publish"], "Resource": [ "arn:aws:iot:us-east-1:123451234510:topic/foo/bar/${iot:ClientId}" ] }] }

In these examples, ${iot:ClientId} is replaced by the ID of the client connected to the AWS IoT 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/foo/${iot:ClientId}/bar" ] }

A client can connect using + as the client ID. This would allow the user to subscribe to any topic matching the topic filter foo/+/bar. To protect against such security gaps, use the iot:Connect policy action to control which client IDs are able to connect. For example, this policy allows only 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" ] }] }