Domain-Protect : Protect Against Subdomain Takeover

• Domain-Protect scans Amazon Route53 across an AWS Organization for domain records vulnerable to takeover
• vulnerable domains in Google Cloud DNS can be detected by Domain Protect for GCP

deploy to security audit account

scan your entire AWS Organization

receive alerts by Slack or email

or manually scan from your laptop

Subdomain Detection Functionality

Scans Amazon Route53 to identify:

• Alias records for CloudFront distributions with missing S3 origin
• CNAME records for CloudFront distributions with missing S3 origin
• ElasticBeanstalk Alias records vulnerable to takeover
• ElasticBeanstalk CNAMES vulnerable to takeover
• Registered domains with missing hosted zones
• Subdomain NS delegations vulnerable to takeover
• S3 Alias records vulnerable to takeover
• S3 CNAMES vulnerable to takeover
• Vulnerable CNAME records for Azure resources
• CNAME records for missing Google Cloud Storage buckets

Optional Additional Check

Turned off by default as it may result in Lambda timeouts for large organisations

• A records for missing storage buckets, e.g. Google Cloud Load Balancer with missing backend storage

To enable, create this Terraform variable in your tfvars file or CI/CD pipeline:

lambdas = [“alias-cloudfront-s3”, “alias-eb”, “alias-s3”, “cname-cloudfront-s3”, “cname-eb”, “cname-s3”, “ns-domain”, “ns-subdomain”, “cname-azure”, “cname-google”, “a-storage”]

Options

1. scheduled lambda functions with email and Slack alerts, across an AWS Organization, deployed using Terraform
2. manual scans run from your laptop or CloudShell, in a single AWS account

Notifications

• Slack channel notification per vulnerability type, listing account names and vulnerable domains
• Email notification in JSON format with account names, account IDs and vulnerable domains by subscribing to SNS topic

Requirements

• Security audit account within AWS Organizations
• Security audit read-only role with an identical name in every AWS account of the Organization
• Storage bucket for Terraform state file
• Terraform 1.0.x

Usage

• replace the Terraform state S3 bucket fields in the command below as appropriate
• for local testing, duplicate terraform.tfvars.example, rename without the .example suffix
• enter details appropriate to your organization and save
• alternatively enter Terraform variables within your CI/CD pipeline

terraform init -backend-config=bucket=TERRAFORM_STATE_BUCKET -backend-config=key=TERRAFORM_STATE_KEY -backend-config=region=TERRAFORM_STATE_REGION
terraform workspace new dev
terraform plan
terraform apply

AWS IAM Policies

For least privilege access control, example AWS IAM policies are provided:

• domain-protect audit policy – attach to domain-protect audit role in every AWS account
• domain-protect audit trust relationship for domain-protect audit role in every AWS account
• domain-protect audit trust relationship with External ID for domain-protect audit role in every AWS account
• domain-protect deploy policy – attach to IAM group or role assumed by CI/CD pipeline

Adding New Checks

• create a new subdirectory within the terraform-modules/lambda/code directory
• add Python code file with same name as the subdirectory
• add the name of the file without extension to var.lambdas in variables.tf
• add a subdirectory within the terraform-modules/lambda/build directory, following the existing naming pattern
• add a .gitkeep file into the new directory
• update the .gitignore file following the pattern of existing directories
• apply Terraform

Adding Notifications To Extra Slack Channels

• add an extra channel to your slack_channels variable list
• add an extra webhook URL or repeat the same webhook URL to your slack_webhook_urls variable list
• apply Terraform

Testing

• use multiple Terraform workspace environments, e.g. dev, prd
• use the slack_channels_dev variable for your dev environment to notify a test Slack channel
• for new subdomain takeover categories, create correctly configured and vulnerable domain names in Route53
• minimise the risk of malicious takeover by using a test domain, with domain names which are hard to enumerate
• remove any vulnerable domains as soon as possible

ci/cd

• infrastructure has been deployed using CircleCI
• environment variables to be entered in CircleCI project settings:

ENVIRONMENT VARIABLE	EXAMPLE VALUE / COMMENT
AWS_ACCESS_KEY_ID	using domain-protect deploy policy
AWS_SECRET_ACCESS_KEY	–
TERRAFORM_STATE_BUCKET	tfstate48903
TERRAFORM_STATE_KEY	domain-protect
TERRAFORM_STATE_REGION	us-east-1
TF_VAR_org_primary_account	012345678901
TF_VAR_security_audit_role_name	not needed if “domain-protect-audit” used
TF_VAR_external_id	only required if External ID is configured
TF_VAR_slack_channels	[“security-alerts”]
TF_VAR_slack_channels_dev	[“security-alerts-dev”]
TF_VAR_slack_webhook_urls	[“https://hooks.slack.com/services/XXX/XXX/XXX”]

• to validate an updated CircleCI configuration:

docker run -v pwd:/whatever circleci/circleci-cli circleci config validate /whatever/.circleci/config.yml