False Negative Rule - AC_AWS_0023 - cloudfrontNoSecureCiphers

[wesleykirklandsg]

• terrascan version: 1.15.2
• Operating System: Mac M1 12.5.1

Description

The following rule provides false negatives. https://github.com/tenable/terrascan/blob/master/pkg/runtime/testdata/testpolicies/aws_cloudfront_distribution/cloudfrontNoSecureCiphers.rego#L7

Tell us what happened, what went wrong, and what you expected to happen. Terrascan outputs the following rule

Description    :    Secure ciphers are not used in CloudFront distribution
File           :    cloudfront.tf
Module Name    :    root
Plan Root      :    ./
Line           :    2
Severity       :    HIGH
Rule Name      :    cloudfrontNoSecureCiphers
Rule ID        :    AC_AWS_0023
Resource Name  :    distribution
Resource Type  :    aws_cloudfront_distribution
Category       :    Data Protection

What I Did

All code is from here - https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/cloudfront_distribution#minimum_protocol_version

Mock TF Code - This passes

resource "aws_s3_bucket" "b" {
  bucket = "mybucket"

  tags = {
    Name = "My bucket"
  }
}

resource "aws_s3_bucket_acl" "b_acl" {
  bucket = aws_s3_bucket.b.id
  acl    = "private"
}

locals {
  s3_origin_id = "myS3Origin"
}

resource "aws_cloudfront_distribution" "s3_distribution" {
  origin {
    domain_name = aws_s3_bucket.b.bucket_regional_domain_name
    origin_id   = local.s3_origin_id

    s3_origin_config {
      origin_access_identity = "origin-access-identity/cloudfront/ABCDEFG1234567"
    }
  }

  enabled             = true
  is_ipv6_enabled     = true
  comment             = "Some comment"
  default_root_object = "index.html"

  logging_config {
    include_cookies = false
    bucket          = "mylogs.s3.amazonaws.com"
    prefix          = "myprefix"
  }

  aliases = ["mysite.example.com", "yoursite.example.com"]

  default_cache_behavior {
    allowed_methods  = ["DELETE", "GET", "HEAD", "OPTIONS", "PATCH", "POST", "PUT"]
    cached_methods   = ["GET", "HEAD"]
    target_origin_id = local.s3_origin_id

    forwarded_values {
      query_string = false

      cookies {
        forward = "none"
      }
    }

    viewer_protocol_policy = "allow-all"
    min_ttl                = 0
    default_ttl            = 3600
    max_ttl                = 86400
  }

  # Cache behavior with precedence 0
  ordered_cache_behavior {
    path_pattern     = "/content/immutable/*"
    allowed_methods  = ["GET", "HEAD", "OPTIONS"]
    cached_methods   = ["GET", "HEAD", "OPTIONS"]
    target_origin_id = local.s3_origin_id

    forwarded_values {
      query_string = false
      headers      = ["Origin"]

      cookies {
        forward = "none"
      }
    }

    min_ttl                = 0
    default_ttl            = 86400
    max_ttl                = 31536000
    compress               = true
    viewer_protocol_policy = "redirect-to-https"
  }

  # Cache behavior with precedence 1
  ordered_cache_behavior {
    path_pattern     = "/content/*"
    allowed_methods  = ["GET", "HEAD", "OPTIONS"]
    cached_methods   = ["GET", "HEAD"]
    target_origin_id = local.s3_origin_id

    forwarded_values {
      query_string = false

      cookies {
        forward = "none"
      }
    }

    min_ttl                = 0
    default_ttl            = 3600
    max_ttl                = 86400
    compress               = true
    viewer_protocol_policy = "redirect-to-https"
  }

  price_class = "PriceClass_200"

  restrictions {
    geo_restriction {
      restriction_type = "whitelist"
      locations        = ["US", "CA", "GB", "DE"]
    }
  }

  tags = {
    Environment = "production"
  }

  viewer_certificate {
    cloudfront_default_certificate = true
    minimum_protocol_version       = "TLSv1"
  }
}

Mock TF Code - This does not pass, it's

resource "aws_s3_bucket" "b" {
  bucket = "mybucket"

  tags = {
    Name = "My bucket"
  }
}

resource "aws_s3_bucket_acl" "b_acl" {
  bucket = aws_s3_bucket.b.id
  acl    = "private"
}

locals {
  s3_origin_id = "myS3Origin"
}

resource "aws_cloudfront_distribution" "s3_distribution" {
  origin {
    domain_name = aws_s3_bucket.b.bucket_regional_domain_name
    origin_id   = local.s3_origin_id

    s3_origin_config {
      origin_access_identity = "origin-access-identity/cloudfront/ABCDEFG1234567"
    }
  }

  enabled             = true
  is_ipv6_enabled     = true
  comment             = "Some comment"
  default_root_object = "index.html"

  logging_config {
    include_cookies = false
    bucket          = "mylogs.s3.amazonaws.com"
    prefix          = "myprefix"
  }

  aliases = ["mysite.example.com", "yoursite.example.com"]

  default_cache_behavior {
    allowed_methods  = ["DELETE", "GET", "HEAD", "OPTIONS", "PATCH", "POST", "PUT"]
    cached_methods   = ["GET", "HEAD"]
    target_origin_id = local.s3_origin_id

    forwarded_values {
      query_string = false

      cookies {
        forward = "none"
      }
    }

    viewer_protocol_policy = "allow-all"
    min_ttl                = 0
    default_ttl            = 3600
    max_ttl                = 86400
  }

  # Cache behavior with precedence 0
  ordered_cache_behavior {
    path_pattern     = "/content/immutable/*"
    allowed_methods  = ["GET", "HEAD", "OPTIONS"]
    cached_methods   = ["GET", "HEAD", "OPTIONS"]
    target_origin_id = local.s3_origin_id

    forwarded_values {
      query_string = false
      headers      = ["Origin"]

      cookies {
        forward = "none"
      }
    }

    min_ttl                = 0
    default_ttl            = 86400
    max_ttl                = 31536000
    compress               = true
    viewer_protocol_policy = "redirect-to-https"
  }

  # Cache behavior with precedence 1
  ordered_cache_behavior {
    path_pattern     = "/content/*"
    allowed_methods  = ["GET", "HEAD", "OPTIONS"]
    cached_methods   = ["GET", "HEAD"]
    target_origin_id = local.s3_origin_id

    forwarded_values {
      query_string = false

      cookies {
        forward = "none"
      }
    }

    min_ttl                = 0
    default_ttl            = 3600
    max_ttl                = 86400
    compress               = true
    viewer_protocol_policy = "redirect-to-https"
  }

  price_class = "PriceClass_200"

  restrictions {
    geo_restriction {
      restriction_type = "whitelist"
      locations        = ["US", "CA", "GB", "DE"]
    }
  }

  tags = {
    Environment = "production"
  }

  viewer_certificate {
    cloudfront_default_certificate = false
    minimum_protocol_version       = "TLSv1"
  }
}

What is happening is the rule seems to be a false negative and states that it's insecure when a custom certificate is specified. The rule should check like so cloudfront_default_certificate = true OR acm_certificate_arn OR iam_certificate_id.

Thanks @mattbarlow-sg for finding this and working through it!

[gaurav-gogia]

Hi @wesleykirklandsg

Thank you for bringing this to our attention. Would you like to take this issue and send a corresponding PR?

[wesleykirklandsg]

@gaurav-gogia I'm unable to do that due to a lack of OPA knowledge. I looked at some samples and could not determine how to do OR logic in this statement. If there is a link/sample I can take another stab at it.