Packer Plugin for Mondoo cnspec

Packer Plugin cnspec by Mondoo scans Linux and Windows HashiCorp Packer builds for vulnerabilities and security misconfigurations. The plugin retrieves CVE data from Mondoo that is updated daily with the latest CVEs and advisories. Additionally, cnspec runs security scans using cnspec-policies to uncover common misconfigurations that open your hosts to the risk of attack. cnspec supports scanning Linux, Windows, and macOS, as well as Docker 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 with Mondoo Platform, and is designed to provide baseline security scanning with minimal configuration. On Linux builds, the plugin runs the Linux Security by Mondoo policy. On Windows builds, the plugin runs the Windows Security by Mondoo policy. Each of these policies provides security hardening checks based on industry standards for Linux and Windows. Scan results display in STDOUT during the Packer run.

• Registered - In registered mode, the plugin is registered with your account in Mondoo Platform using a service account. This 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.

Configuration Options

The packer-plugin-cnspec plugin supports a wide range of configuration options to customize scanning behavior, authentication, output, and policy usage. These options can be set directly in your Packer template or via environment variables where applicable.

Plugin Configuration Fields

Field	Type	Description
annotations	map[string]string	Key/value annotations to assign to scanned assets.
asset_name	string	Custom asset name to display in Mondoo Platform. Defaults to instance hostname.
debug	bool	Enables debug logging.
host_alias	string	Alias by which the host should be identified in Mondoo Platform. Defaults to default.
incognito	bool	Disables sending scan results to Mondoo Platform. Defaults to automatic detection.
labels	map[string]string	Key/value labels to assign to scanned assets.
local_port	uint	Starting port to listen for SSH connections. Defaults to system-assigned port if not set.
mondoo_config_path	string	Path to the Mondoo service account YAML file. Defaults to $HOME/.config/mondoo/mondoo.yml.
on_failure	string	Behavior when score_threshold is not met. Options: continue or fail. Default: fail.
output	string	Output format. Options: compact, csv, full, json, junit, report, summary, yaml. Default: compact.
output_target	string	Target path for saving output. Optional.
policies	[]string	List of policy paths or URLs to use instead of defaults. Enables incognito mode.
policybundle	string	Path to a local .tar.gz policy bundle.
score_threshold	int	Integer threshold for scan score. Builds fail if the score is below this value. Default: 0.
ssh_authorized_key_file	string	Path to public key of SSH user. Defaults to autogenerated one-time key.
ssh_host_key_file	string	Path to SSH key used for forwarding commands. Defaults to autogenerated one-time key.
sudo	*SudoConfig	Runs scan with --sudo when applicable.
use_proxy	bool	Use proxy to connect to the host. Falls back to Packer’s communicator proxy if needed.
use_scp	bool	Use SCP instead of SFTP. Not recommended on Windows 2025. Default: false.
use_sftp	bool	(Deprecated) Use SFTP for file transfers. Default: true.
user	string	The user for SSH connection. Defaults to the communicator's configured user.
winrm_password	string	WinRM password for Windows instances. Defaults to communicator’s password.
winrm_user	string	WinRM user for Windows instances. Defaults to communicator’s user.

Environment Variables

Some configuration options can also be set using environment variables, especially those related to authentication:

Environment Variable	Description
MONDOO_CONFIG_PATH	Path to the Mondoo service account YAML file. Equivalent to mondoo_config_path.
MONDOO_CONFIG_BASE64	Base64-encoded Mondoo service account config. Used in CI/CD environments or inline secrets.

For more information about Mondoo service accounts, refer to the official documentation:
https://mondoo.com/docs/platform/maintain/access/non-human/service_accounts/

Tutorials

Check out the Packer tutorials on the Mondoo documentation site:

• Build Secure AMIs with cnspec and HashiCorp Packer

• Build Secure VM Images in Google Cloud with cnspec and HashiCorp Packer

Install Packer plugin cnspec

You can install Packer Plugin cnspec using the packer init command, install it manually, or build it from source.

Install using the packer init command

As of version 1.7, Packer's packer init command allows automatic installation of Packer plugins. For more information, read the Packer documentation.

To install Packer Plugin cnspec:

1. Copy and paste this code into your Packer configuration.

packer {
  required_plugins {
    cnspec = {
      version = "~> 12"
      source  = "github.com/mondoohq/cnspec"
    }
  }
}

2. Run this command:

packer init /path/to/template.pkr.hcl

Install manually

You can find pre-built binary releases of the plugin here.

Once you have downloaded the latest archive corresponding to your target OS, uncompress it to retrieve the plugin binary file corresponding to your platform. To install the plugin, follow the Packer documentation on installing a plugin.

Build from source

If you prefer to build the plugin from source:

1. Clone this GitHub repository locally.

2. Run this command from the root directory: go build

3. After you successfully compile, the packer-plugin-cnspec plugin binary file is in the root directory. Copy the binary into ~/.packer.d/plugins/ by running this command: make dev

4. To install the compiled plugin, follow the Packer documentation on installing plugins.

After building the cnspec plugin successfully, use the latest version of Packer to build a machine and verify your changes. In the example folder we provide a basic template. To force Packer to use the development binary installed in the previous step, comment out the packer {} block.

To use the developer plugin, set the packer plugin environment variable:

export PACKER_PLUGIN_PATH=~/.packer.d/plugins
packer build amazon-linux-2.pkr.hcl

Configure Packer Plugin cnspec

For detailed instructions on configuring the Packer Plugin cnspec, please visit the official HashiCorp documentation at Packer Plugin cnspec. There you'll find comprehensive guidance on setup and configuration options.

Sample Packer Templates

You can find example Packer templates in the examples directory in this repository. You can also find a GitHub Action workflow example of how to use cnspec to test builds as part of a CI/CD pipeline.

Get Started with cnspec

cnspec's benefits extend well beyond securing Packer builds! To start exploring, download cnspec.

Contributing

If you think you've found a bug in the code or you have a question about using this software, please reach out to us by opening an issue in this GitHub repository.

Contributions to this project are welcome! If you want to fix a bug, please do so by opening a pull request in this GitHub repository. If you want to add a feature, please start by opening an issue in this GitHub repository to discuss it with us beforehand.

Join the community!

Join the Mondoo Community GitHub Discussions to collaborate on policy as code and security automation.