AWS S3 Alias Records Vulnerable To Takeover

Using Console

Sign in to the AWS Management Console.
Navigate to the Route 53 service.
Select Hosted zones from the navigation pane.
Identify vulnerable DNS Alias records:
- Look for Alias records that point to S3 buckets with website hosting enabled.
Review Alias record settings:
- Click on each vulnerable record.
- Review the Alias Target to ensure it points to a secure S3 bucket.
Secure the S3 bucket:
- If the S3 bucket is configured insecurely (e.g., publicly accessible), modify its permissions to restrict access as necessary.
Repeat for other vulnerable records:
- Repeat the above steps for all vulnerable DNS Alias records.

Using CLI

Identify Vulnerable S3 Alias Records:
- List all Route 53 hosted zones and alias records pointing to S3 buckets.
aws route53 list-hosted-zones
aws route53 list-resource-record-sets --hosted-zone-id HOSTED_ZONE_ID
Replace HOSTED_ZONE_ID with the ID of each hosted zone.

Update S3 Bucket Policies:

For each S3 bucket referenced in the alias record, ensure that the bucket is not publicly accessible or misconfigured. You can update the bucket policy to deny access from all principals using the AWS CLI. Here’s an example command:

aws s3api put-bucket-policy --bucket BUCKET_NAME --policy '{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Deny",
            "Principal": "*",
            "Action": "s3:GetObject",
            "Resource": "arn:aws:s3:::BUCKET_NAME/*"
        }
    ]
}'

Replace BUCKET_NAME with the name of the S3 bucket.

Verify Remediation:
- After updating the bucket policy, verify that the S3 buckets are not publicly accessible or misconfigured.
aws s3api get-bucket-policy --bucket BUCKET_NAME
Replace BUCKET_NAME with the name of the S3 bucket.
Repeat for Other Vulnerable Records:
- Repeat the above steps for each vulnerable S3 alias record identified.

By updating the bucket policy to deny access from all principals, you effectively remove public access to the S3 bucket. Make sure to review and adjust the bucket policy according to your specific requirements and access control needs. Also, ensure that you have the necessary permissions to update S3 bucket policies.This remediation assumes that the S3 buckets should not be publicly accessible. If public access is required, ensure that appropriate security measures are in place to protect the data.

Using Python

Here’s a Python script to identify and remediate vulnerable DNS Alias records:

import boto3

class DNSAliasChecker:
    def __init__(self):
        self.route53_client = boto3.client('route53')
        self.s3_client = boto3.client('s3')

    def get_vulnerable_alias_records(self):
        failures = []
        response = self.route53_client.list_hosted_zones()
        for hosted_zone in response['HostedZones']:
            hosted_zone_id = hosted_zone['Id'].split('/')[-1]
            records = self.route53_client.list_resource_record_sets(HostedZoneId=hosted_zone_id)
            for record in records['ResourceRecordSets']:
                if self.is_record_vulnerable(record):
                    failures.append(record)
        return failures

    def is_record_vulnerable(self, record):
        alias_target = record.get("AliasTarget", {})
        if "amazonaws.com" in alias_target.get("DNSName", "") and "s3-website" in alias_target.get("DNSName", ""):
            return True
        return False

    def remediate_vulnerable_record(self, record_name):
        # Implement remediation logic here
        print(f"Record {record_name} has been remediated.")

# Instantiate the class
checker = DNSAliasChecker()

# Get vulnerable alias records
vulnerable_records = checker.get_vulnerable_alias_records()

# Remediate vulnerable records
for record in vulnerable_records:
    checker.remediate_vulnerable_record(record['Name'])

This Python script identifies DNS Alias records vulnerable to S3 buckets and provides a placeholder for the remediation logic. You would need to implement the logic to secure the referenced S3 buckets.Make sure to have appropriate IAM permissions for managing Route 53 hosted zones and S3 buckets if you’re using AWS CLI or Python script.

Using Terraform

# This aws_route53_record represents the vulnerable alias record that should be deleted.
resource "aws_route53_record" "VULNERABLE_ALIAS_RECORD" {
  zone_id = "HOSTED_ZONE_ID"          # replace with the hosted zone ID (e.g., Z123EXAMPLE)
  name    = "VULNERABLE_NAME.example.com."  # replace with the exact record name (must include trailing dot)
  type    = "A"                       # or "AAAA", etc., to match the existing record

  alias {
    name                   = "ALIAS_TARGET_DNS_NAME"     # e.g., "example-bucket.s3-website-us-east-1.amazonaws.com."
    zone_id                = "ALIAS_TARGET_HOSTED_ZONE_ID" # HostedZoneId from the existing alias target
    evaluate_target_health = false                        # match the current value
  }
}

To remediate, delete this aws_route53_record block from your Terraform configuration (or set count = 0 on it); on the next terraform apply Terraform will permanently remove the DNS alias record from Route 53, and the domain name will no longer resolve. This is a destructive change and may cause an outage if the record is still needed—confirm it is safe to remove before applying.Verification: terraform plan should show this record with a - destroy action in the Route 53 hosted zone.

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AWS S3 Alias Records Vulnerable To Takeover

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