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1.18 Use Identity and Access Management (IAM) instance roles for AWS resource access from instances (Manual)​

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Description​

Control AWS access from within AWS instances by either encoding AWS keys into AWS API calls or by assigning the instance to a role which has an appropriate permissions policy for the required access. "AWS Access" means accessing the APIs of AWS to access AWS resources or manage AWS account resources.

Rationale​

AWS IAM roles reduce the risks associated with sharing and rotating credentials that can be used outside of AWS itself. If credentials are compromised, they can be used from outside of the AWS account they give access to. In contrast, in order to leverage role permissions an attacker would need to gain and maintain access to a specific instance to use the privileges associated with it.

Additionally, if credentials are encoded into compiled applications or other hard to change mechanisms, then they are even more unlikely to be properly rotated due to service disruption risks. As time goes on, credentials that cannot be rotated are more likely to be known by an increasing number of individuals who no longer work for the organization owning the credentials.

Audit​

Where an instance is associated with a Role:

For instances that are known to perform AWS actions, ensure that they belong to an instance role that has the necessary permissions:

  1. Login to AWS Console (with appropriate permissions to View Identity Access Management Account Settings)
  2. Open the EC2 Dashboard and choose "Instances"
  3. Click the EC2 instance that performs AWS actions, in the lower pane details find "IAM Role"
  4. If the Role is blank, the instance is not assigned to one.
  5. If the Role is filled in, it does not mean the instance might not *also* have credentials encoded on it for some activities.

Where an Instance Contains Embedded Credentials:

  • On the instance that is known to perform AWS actions, audit all scripts and environment variables to ensure that none of them contain AWS credentials.

Where an Instance Application Contains Embedded Credentials:

  • Applications that run on an instance may also have credentials embedded. This is a bad practice, but even worse if the source code is stored in a public code repository such as github. When an application contains credentials can be determined by eliminating all other sources of credentials and if the application can still access AWS resources - it likely contains embedded credentials. Another method is to examine all source code and configuration files of the application.

Remediation​

It is only possible to associate IAM roles at the launch of an instance. To remediate an instance to add it to a role you must create a new instance.

If the instance has no external dependencies on its current private ip or public addresses are elastic IPs:

  1. In AWS IAM create a new role. Assign a permissions policy if needed permissions are already known.
  2. In the AWS console launch a new instance with identical settings to the existing instance, and select the newly created role.
  3. Shutdown both the existing instance and the new instance.
  4. Detach disks from both instances.
  5. Attach the existing instance disks to the new instance.
  6. Boot the new instance and you should have the same machine, but with the associated role.
note

If your environment has dependencies on a dynamically assigned PRIVATE IP address you can create an Amazon Machine Image (AMI) from the existing instance, destroy the old one and then when launching from the AMI, manually assign the previous private IP address.

note

If your environment has dependencies on a dynamically assigned PUBLIC IP address there is not a way to retain the address and assign an instance role. Dependencies on dynamically assigned public IP addresses are a bad practice and, if possible, you may wish to rebuild the instance with a new elastic IP address and make the investment to remediate affected systems while assigning the system to a role.

References​

https://docs.aws.amazon.com/IAM/latest/UserGuide/id_roles_use_switch-role-ec2.html
https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/iam-roles-for-amazon-ec2.html

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