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S3 Buckets Should Have A Secure Transport Policy

More Info:​

AWS S3 buckets should enforce encryption of data over the network (as it travels to and from Amazon S3) using Secure Sockets Layer (SSL).

Risk Level​

Critical

Address​

Security

Compliance Standards​

  • APRA CPS 234 (Australia)
  • AWS Startup Security Baseline
  • AWS Well Architected Framework
  • BSI C5 (Germany)
  • Brazil LGPD
  • CCPA / CPRA (California)
  • CIS AWS
  • CIS Critical Security Controls v8
  • CMMC 2.0
  • CSA Cloud Controls Matrix v4
  • Cloudanix Best Practice
  • DPDPA
  • Digital Operational Resilience Act (EU)
  • GDPR
  • HIPAA
  • HITRUST CSF
  • ISO 27001
  • ISO/IEC 27017
  • ISO/IEC 27018
  • ISO/IEC 27701
  • KSA PDPL
  • MAS Technology Risk Management (Singapore)
  • MITRE ATT&CK (Cloud)
  • NIS2 Directive
  • NIST
  • NIST CSF
  • NIST SP 800-171
  • NYDFS 23 NYCRR 500
  • PCI
  • Reserve Bank of India (RBI) Cyber Security Framework
  • Reserve Bank of India (RBI) Master Direction – Information Technology Framework
  • SOC2
  • SWIFT Customer Security Controls Framework
  • Sarbanes-Oxley IT General Controls
  • UK NCSC Cyber Assessment Framework

Triage and Remediation​

Remediation​

Using Console
  1. Open the AWS S3 Console.
  2. Navigate to the specific S3 bucket for which you want to enforce secure transport.
  3. Click on the "Permissions" tab.
  4. Scroll down to the "Bucket policy" section.
  5. Edit the bucket policy to enforce the use of HTTPS.

Here is an example policy snippet to enforce HTTPS:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "DenyNonSSLRequests",
            "Effect": "Deny",
            "Principal": "*",
            "Action": "s3:*",
            "Resource": [
                "arn:aws:s3:::YOUR_BUCKET_NAME/*",
                "arn:aws:s3:::YOUR_BUCKET_NAME"
            ],
            "Condition": {
                "Bool": {
                    "aws:SecureTransport": "false",
                    "aws:PrincipalIsAWSService": "false"
                }
            }
        }
    ]
}

Replace YOUR_BUCKET_NAME with the name of your S3 bucket.

Using CLI
# Run the following AWS CLI command to update the bucket policy to enforce HTTPS
aws s3api put-bucket-policy --bucket YOUR_BUCKET_NAME --policy '{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Sid": "DenyNonSSLRequests",
      "Effect": "Deny",
      "Principal": "*",
      "Action": "s3:*",
      "Resource": ["arn:aws:s3:::YOUR_BUCKET_NAME/*", "arn:aws:s3:::YOUR_BUCKET_NAME"],
      "Condition": {
        "Bool": {
          "aws:SecureTransport": "false",
          "aws:PrincipalIsAWSService": "false"
        }
      }
    }
  ]
}'

Replace YOUR_BUCKET_NAME with the name of your S3 bucket.

Using Python
import boto3

def remediate_s3_secure_transport_policy(bucket_name, aws_access_key_id, aws_secret_access_key, region):
    # Create an S3 client
    s3_client = boto3.client('s3', aws_access_key_id=aws_access_key_id, aws_secret_access_key=aws_secret_access_key, region_name=region)

    # Bucket policy to enforce secure transport (HTTPS)
    bucket_policy = {
        "Version": "2012-10-17",
        "Statement": [
            {
                "Sid": "DenyNonSSLRequests",
                "Effect": "Deny",
                "Principal": "*",
                "Action": "s3:*",
                "Resource": [
                    f"arn:aws:s3:::{bucket_name}/*",
                    f"arn:aws:s3:::{bucket_name}"
                ],
                "Condition": {
                    "Bool": {
                        "aws:SecureTransport": "false",
                        "aws:PrincipalIsAWSService": "false"
                    }
                }
            }
        ]
    }

    # Apply the bucket policy
    s3_client.put_bucket_policy(
        Bucket=bucket_name,
        Policy=json.dumps(bucket_policy)
    )

    print(f"Secure transport policy (HTTPS) enforced for S3 bucket: {bucket_name}")

# Example usage
bucket_name = 'YOUR_BUCKET_NAME'
aws_access_key_id = 'YOUR_ACCESS_KEY'
aws_secret_access_key = 'YOUR_SECRET_KEY'
region = 'us-east-1'  # Replace with your desired region

remediate_s3_secure_transport_policy(bucket_name, aws_access_key_id, aws_secret_access_key, region)

Replace YOUR_BUCKET_NAME, YOUR_ACCESS_KEY, YOUR_SECRET_KEY, and update the region with your desired region in the Python script. Run the script, and it will enforce the use of HTTPS for the specified S3 bucket. Make sure to install the boto3 library if you haven't already:

pip install boto3

Note: Ensure that you have the necessary permissions to make these changes, and exercise caution when applying changes to production environments.

Using Terraform
resource "aws_s3_bucket" "this" {
  bucket = "BUCKET_NAME" # replace with your bucket name
}

data "aws_iam_policy_document" "secure_transport" {
  # If you already have a bucket policy, merge its statements into this
  # data block instead of replacing it outright.
  statement {
    sid    = "DenyNonHTTPS"
    effect = "Deny"

    principals {
      type        = "*"
      identifiers = ["*"]
    }

    actions = ["s3:*"]

    resources = [
      aws_s3_bucket.this.arn,
      "${aws_s3_bucket.this.arn}/*",
    ]

    condition {
      test     = "Bool"
      variable = "aws:SecureTransport"
      values   = ["false"]
    }
  }
}

resource "aws_s3_bucket_policy" "secure_transport" {
  bucket = aws_s3_bucket.this.id
  policy = data.aws_iam_policy_document.secure_transport.json
}

This enforces HTTPS-only access via a bucket policy equivalent to the provided CLI put-bucket-policy call; it updates the existing policy in place (no bucket replacement), but it will overwrite any previous policy unless you merge other required statements into the aws_iam_policy_document.

Verification: terraform plan should show an aws_s3_bucket_policy resource being created or updated with a Deny statement on s3:* for the bucket and all objects when aws:SecureTransport is false.

Additional Reading:​