Build Secure AMIs with cnspec and HashiCorp Packer

You can run security scans during HashiCorp Packer builds using Packer plugin cnspec by Mondoo. This tutorial includes instructions for using the plugin both with and without an account on Mondoo Platform.

caution

This tutorial provisions resources that qualify under the AWS Free Tier. If your account doesn't qualify under the AWS Free Tier, Mondoo is not responsible for charges that you incur.

Prerequisites

Before you begin, be sure you have:

An AWS Account
The AWS CLI installed and configured
The latest HashiCorp Packer version installed

Packer plugin cnspec by Mondoo

Packer plugin cnspec by Mondoo scans Linux and Windows HashiCorp Packer builds for vulnerabilities and security misconfigurations. The plugin is designed to work with any of the supported Packer builders, including containers.

Plugin modes

Packer plugin cnspec is designed to work in one of two modes:

Unregistered - In unregistered mode, the plugin works without being registered to Mondoo Platform, and is designed to provide baseline security scanning with minimal configuration. The plugin runs either the Linux Security by Mondoo policy on Linux builds, or the Windows Security by Mondoo policy on Windows builds. Each of these policies provides security hardening checks based off of industry standards for Linux and Windows. Scan results are shown in STDOUT during the Packer run.
Registered - In registered mode, the plugin is registered to your account in Mondoo Platform using a service account. Registered mode allows you to configure and customize any of the policies in Mondoo Platform including CIS benchmarks and more. Scan results are shown in STDOUT and sent back to Mondoo Platform for your records.

info

To scan for vulnerabilities, you must register cnspec with Mondoo Platform. Sign up for a free account today.

AWS authentication

Before you can run Packer, you must configure AWS credentials with appropriate permissions to build AMIs. For more information see Configuring the AWS CLI in the AWS documentation.

For a full list of IAM permissions required to run the amazon-ebs builder, refer to the Packer Amazon AMI Builder documentation.

tip

If you don't have access to IAM user credentials, use another authentication method described in the Packer Amazon AMI Builder documentation.

Plugin configuration

Packer plugin cnspec provides this configuration:

score_threshold - This configuration sets an int score threshold for security scans. If the scan produces a score that falls below the threshold, the build will fail.
on_failure = "continue" - This configuration ensures that the Packer build will not fail even if the scan produces a score that falls below the score_threshold.
sudo - Some of the security configuration checks require elevated permissions to scan a given resource such as the sshd_config. Setting the sudo option to active = true configures the plugin to run in sudo mode.
asset_name - Override the asset name on Mondoo Platform. This configuration is only used in registered mode.
annotations - Custom annotations can be applied to Packer build assets to provide additional metadata for asset tracking. This configuration is only used in registered mode.

Register with Mondoo Platform

To configure the plugin to work in registered mode, you must first create a Base64-encoded service account. If you do not wish to use custom policies and store results on Mondoo Platform you can skip this step.

To create a Base64-encoded service account:

Navigate to the space in which you want to create a service account.
In the left navigation, select Settings. Then select the Service Accounts tab.
Select ADD ACCOUNT.
Check the Base64-encoded box to Base64-encode the credentials.
Select GENERATE NEW CREDENTIALS.
Copy the Base64-encoded credentials to the clipboard.
Open a terminal and run:

export MONDOO_CONFIG_BASE64=<paste Base64-encoded token>

Run Packer

With Packer configured, you are ready to run your first build.

Amazon Linux 2 template

Create a new directory named mondoo_packer, and change to that directory.

mkdir mondoo_packer
cd mondoo_packer

Create a new file called aws-amazon2.pkr.hcl, and then copy/paste this code snippet into that file.

packer {
  required_plugins {
    amazon = {
      version = ">= 1.1.0"
      source  = "github.com/hashicorp/amazon"
    }
    cnspec = {
      version = ">= 6.1.3"
      source  = "github.com/mondoohq/cnspec"
    }
  }
}

variable "aws_region" {
  default = "us-east-1"
  type    = string
}

variable "image_prefix" {
  type = string
  description = "Prefix to be applied to image name"
  default = "cnspec-tested-amazon-linux-2"
}

locals { timestamp = regex_replace(timestamp(), "[- TZ:]", "") }

source "amazon-ebs" "amazon2" {
  ami_name      = "${var.image_prefix}-${local.timestamp}"
  instance_type = "t2.micro"
  region        = var.aws_region
  source_ami_filter {
    filters = {
      name                = "amzn2-ami-kernel-5.*-x86_64-gp2"
      root-device-type    = "ebs"
      virtualization-type = "hvm"
    }
    most_recent = true
    owners      = ["137112412989"]
  }
  ssh_username = "ec2-user"
  tags = {
    Base_AMI_Name = "{{ .SourceAMIName }}"
    Name          = "${var.image_prefix}-${local.timestamp}"
    Source_AMI    = "{{ .SourceAMI }}"
    Creation_Date = "{{ .SourceAMICreationDate }}"
  }
}

build {
  name = "${var.image_prefix}-${local.timestamp}"

  sources = [
    "source.amazon-ebs.amazon2"
  ]

  provisioner "shell" {
    inline = [
      "sudo hostnamectl set-hostname ${var.image_prefix}-${local.timestamp}",
      "sudo yum update -y",
      "sudo yum upgrade -y"]
  }

  provisioner "cnspec" {
    score_threshold = 80
    on_failure = "continue"
    sudo {
      active = true
    }
  }
}

This is a complete Packer template that you will use to build an AWS Amazon 2 Linux AMI in the us-east-1 region. In these sections, you will review each block of this template in more detail.

Configure template variables

The template provides a variables section used to configure the builds.

info

To learn about the various options to override variables set in the Packer template, see Setting Variables in the HashiCorp Packer documentation.

AWS region

When building AMIs, you must specify which region to build the AMI in. The default region for the template is us-east-1:

variable "aws_region" {
  default = "us-east-1"
  type    = string
}

tip

Use the optional ami_regions to configure a list of regions to copy the AMI to. Tags and attributes are copied along with the AMI.

Image prefix

By default the template will create the AMI using a default naming prefix of cnspec-tested-amazon-linux-2. You can override this with the image_prefix variable:

variable "image_prefix" {
  type = string
  description = "Prefix to be applied to image name"
  default = "cnspec-tested-amazon-linux-2"
}

Initialize the Packer configuration

Initialize your Packer configuration.

packer init aws-amazon2.pkr.hcl

Executing packer init instructs Packer to download the plugins defined in the required_plugins section in the template. Plugins are typically downloaded to the ~/.packer.d/pluginsdirectory. You can run packer init as many times as you'd like. If you already have the plugins you need, Packer exits without output.

Build the AMI

Build the image with the packer build aws-amazon2.pkr.hcl command. Packer prints output similar to what is shown below.

packer build aws-amazon2.pkr.hcl
<image-name>.amazon-ebs.amazon2: output will be in this color.

==> <image-name>.amazon-ebs.amazon2: Prevalidating any provided VPC information
==> <image-name>.amazon-ebs.amazon2: Prevalidating AMI Name: <image-name>
    <image-name>.amazon-ebs.amazon2: Found Image ID: ami-0b0dcb5067f052a63
==> <image-name>.amazon-ebs.amazon2: Creating temporary keypair: packer_6382573a-e356-c04a-958f-c1ece4083785
==> <image-name>.amazon-ebs.amazon2: Creating temporary security group for this instance: packer_6382573d-6f07-acc1-f218-df04593a22f1
...
==> <image-name>.amazon-ebs.amazon2: Running cnspec packer provisioner by Mondoo (Version: 0.6.0, Build: dev)
    <image-name>.amazon-ebs.amazon2: activated sudo
    <image-name>.amazon-ebs.amazon2: detected packer build via ssh
    <image-name>.amazon-ebs.amazon2: scan packer build
    <image-name>.amazon-ebs.amazon2: scan completed successfully
...

    <image-name>.amazon-ebs.amazon2: ✕ Fail:  D  20  Ensure sudo logging is enabled
    <image-name>.amazon-ebs.amazon2: ✕ Fail:  D  20  Ensure kernel module loading and unloading is collected
    <image-name>.amazon-ebs.amazon2: ✓ Pass:  Ensure no duplicate UIDs exist
    <image-name>.amazon-ebs.amazon2: ✕ Fail:  D  20  Ensure unsuccessful unauthorized file access attempts are collected
    <image-name>.amazon-ebs.amazon2: ✓ Pass:  Ensure prelink is disabled
    <image-name>.amazon-ebs.amazon2: ✕ Fail:  F   0  Ensure that strong Key Exchange algorithms are used
    <image-name>.amazon-ebs.amazon2: ✓ Pass:  Ensure Samba is stopped and not enabled
    <image-name>.amazon-ebs.amazon2:
    <image-name>.amazon-ebs.amazon2: Vulnerabilities:
    <image-name>.amazon-ebs.amazon2: ■ No advisories found (passed)
    <image-name>.amazon-ebs.amazon2:
    <image-name>.amazon-ebs.amazon2: Overall CVSS score: 0.0
    <image-name>.amazon-ebs.amazon2:
    <image-name>.amazon-ebs.amazon2:
    <image-name>.amazon-ebs.amazon2: Summary (1 assets)
    <image-name>.amazon-ebs.amazon2: ==================
    <image-name>.amazon-ebs.amazon2:
    <image-name>.amazon-ebs.amazon2: Target:     i-0dd30e6f234216dd1
    <image-name>.amazon-ebs.amazon2: Score:      C    50/100     (100% completed)
    <image-name>.amazon-ebs.amazon2: ✓ Passed:   ████████ 52% (55)
    <image-name>.amazon-ebs.amazon2: ✕ Failed:   ███████ 44% (46)
    <image-name>.amazon-ebs.amazon2: ! Errors:   3% (3)
    <image-name>.amazon-ebs.amazon2: » Skipped:  1% (1)
    <image-name>.amazon-ebs.amazon2:
    <image-name>.amazon-ebs.amazon2: Policies:
    <image-name>.amazon-ebs.amazon2: F   0  Linux Security by Mondoo
    <image-name>.amazon-ebs.amazon2: A 100  Platform Vulnerability Policy by Mondoo
...
==> Wait completed after 10 minutes 7 seconds

==> Builds finished. The artifacts of successful builds are:
--> <image-name>.amazon-ebs.amazon2: AMIs were created:
us-east-1: ami-0b3e9a14e02dd8f37

View the scan report in Mondoo Platform (registered mode only)

To view the scan report in the Mondoo Console, go to INVENTORY and find the report. You might need to refresh your browser.

Mondoo scan report from HashiCorp Packer build

View the control details

Select the Controls tab.

Controls tab in a Mondoo scan report from HashiCorp Packer build

Expand any of the checks in the policies that ran against your build to show additional documentation, audit, and remediation steps:

Control details in a Mondoo scan result

View the image AWS Management Console

Mondoo secure base image in AWS Management Console

After running the above example, you can navigate to the AMIs section of AWS Management Console.

Remove the image

You can remove the AMI by first deregistering it on the AWS AMI management page. Next, delete the associated snapshot on the AWS snapshot management page.

Next steps

In this tutorial, you built an Amazon AMI and scanned it for vulnerabilities and security misconfigurations with cnspec.

The GitHub repository for Packer plugin cnspec contains additional templates for building Ubuntu and Windows images.

Prerequisites​

Packer plugin cnspec by Mondoo​

Plugin modes​

AWS authentication​

Plugin configuration​

Register with Mondoo Platform​

Run Packer​

Amazon Linux 2 template​

Configure template variables​

Initialize the Packer configuration​

Build the AMI​

View the scan report in Mondoo Platform (registered mode only)​

View the control details​

View the image AWS Management Console​

Remove the image​

Next steps​