Table of Contents

• Introduction
• 4,000+ open source projects use Harden-Runner
  • Trusted By
  • Case Studies
• Why use Harden-Runner
• Getting Started
  • Hardening GitHub-Hosted Runners
    • Hands-On Tutorials
  • Support for Private Repositories
  • Hardening Self-Hosted Runners
    • Self-Hosted Actions Runner Controller (ARC) Runners
    • Self-Hosted VM Runners (e.g. on EC2)
• Features at a glance
  • View outbound network traffic at the job level
  • View outbound network traffic at the organization level
  • View outbound HTTPS traffic at the job level
  • Detect anomalous outbound network traffic
  • Filter outbound network traffic to allowed endpoints
  • Determine minimum GITHUB_TOKEN permissions using Harden-Runner
  • View the name and path of every file written during the build process
  • View process names and arguments
  • Detect tampering of source code during build
  • Run your job without sudo access
  • Get real-time security alerts
• Discussions
• How does it work?
  • GitHub-Hosted Runners
  • Self-Hosted Actions Runner Controller (ARC) Runners
  • Self-Hosted VM Runners (e.g. on EC2)
• Limitations
  • GitHub-Hosted Runners
  • Self-Hosted Actions Runner Controller (ARC) Runners
  • Self-Hosted VM Runners (e.g. on EC2)

Introduction

Harden-Runner provides network egress filtering and runtime security for GitHub-hosted and self-hosted runners. It is called Harden-Runner because it hardens the runner on which GitHub Actions workflows run.

Learn how Harden-Runner works through the video below, which shows how it detected a supply chain attack on a Google open-source project.

4,000+ open source projects use Harden-Runner

Harden-Runner is trusted by leading open source projects and enterprises to secure their CI/CD pipelines.

Trusted by

CISA Explore	Microsoft Explore	Google Explore	DataDog Explore	Intel Explore	Kubernetes Explore	Node.js Explore	AWS Explore

Case Studies

• Harden-Runner Detects CI/CD Supply Chain Attack in Google’s Open-Source Project Flank
• Kapiche secures their GitHub Actions software supply chain with Harden-Runner
• Arcjet Enhances CI/CD Security with Harden-Runner

Why use Harden-Runner

There are two main threats from compromised workflows, dependencies, and build tools in a CI/CD environment:

1. Exfiltration of CI/CD credentials and source code
2. Tampering of source code, dependencies, or artifacts during the build to inject a backdoor

Harden-Runner monitors process, file, and network activity to:

	Countermeasure	Prevent Security Breach
1.	Monitor and block outbound network traffic at the DNS, HTTPS (Layer 7), and network layers (Layers 3 and 4) to prevent exfiltration of code and CI/CD credentials	To prevent the Codecov breach scenario
2.	Detect if source code is being tampered during the build process to inject a backdoor	To detect the XZ Utils and SolarWinds incident scenarios
3.	Detect poisoned workflows and compromised dependencies that exhibit suspicious behavior	To detect Dependency confusion and Malicious dependencies scenarios
4.	Determine minimum GITHUB_TOKEN permissions by monitoring HTTPS calls to GitHub APIs	To set minimum GITHUB_TOKEN permissions to reduce the impact of exfiltration

Getting Started

Hardening GitHub-Hosted Runners

1. Add the step-security/harden-runner GitHub Action to your GitHub Actions workflow file as the first step in each job. You can automate adding Harden-Runner Action to your workflow file by pasting your workflow in the StepSecurity online tool.

   steps:
     - uses: step-security/harden-runner@446798f8213ac2e75931c1b0769676d927801858 # v2.10.0
       with:
         egress-policy: audit

2. In the workflow logs and the job markdown summary, you will see a link to security insights and recommendations.

   

3. Click on the link (example link). You will see a process monitor view of network and file events correlated with each step of the job.

   

4. In the Recommended Policy tab, you'll find a recommended block policy based on outbound calls aggregated from the current and past runs of the job. You can update your workflow file with this policy, or alternatively, use the Policy Store to apply the policy without modifying the workflow file. From now on, any outbound calls not in the allowed list will be blocked.

   

Hands-On Tutorials

You can use GitHub Actions Goat to try Harden-Runner. You only need a GitHub Account and a web browser.

Hands-on Tutorials for GitHub Actions Runtime Security:

1. Filter Egress Network Traffic
2. Detect File Tampering

Support for Private Repositories

Hardening of runners used in private repositories is supported with a commercial license. Check out the documentation for more details.

• To use Harden-Runner in a Private repository, you must install the StepSecurity GitHub App.
• This is needed to access the GitHub Actions API and to authenticate users to access the dashboard for private repositories.
• If you use Harden-Runner GitHub Action in a private repository, the generated insights URL is NOT public. Only those who have access to the repository can view it.

Read this case study on how Kapiche uses Harden-Runner to improve software supply chain security in their private repositories.

Hardening Self-Hosted Runners

Hardening of self-hosted runners is supported with a commercial license. Check out the documentation for more details. For hardening of self-hosted runners you must install the StepSecurity GitHub App.

Self-Hosted Actions Runner Controller (ARC) Runners

Explore demo workflows using self-hosted ARC Runner and ARC Harden-Runner here.

Actions Runner Controller (ARC) is a Kubernetes operator that orchestrates self-hosted runners for GitHub Actions.

• Instead of adding the Harden-Runner GitHub Action in each job, you'll need to install the ARC Harden-Runner daemonset on your Kubernetes cluster.
• Upon installation, the ARC Harden-Runner daemonset monitors all jobs run on the cluster; you do NOT need to add the Harden-Runner GitHub Action to each job for audit mode. You do need to add the Harden-Runner GitHub Action to jobs where you want to enable block mode.
• The instructions for installing the ARC-Harden-Runner daemonset are shown in the dashboard. To enable access to these instructions, please email support@stepsecurity.io.

Self-Hosted VM Runners (e.g. on EC2)

Explore demo workflows using self-hosted VM Runners and Harden-Runner here.

• Instead of adding the Harden-Runner GitHub Action in each job, you'll need to install the Harden-Runner agent on your runner image (e.g. AMI). This is typically done using packer or as a post-install step when using the https://github.com/philips-labs/terraform-aws-github-runner project to setup runners.
• The Harden-Runner agent monitors all jobs run on the VM, both ephemeral and persistent runners are supported; you do NOT need to add the Harden-Runner GitHub Action to each job for audit mode. You do need to add the Harden-Runner GitHub Action to jobs where you want to enable block mode.
• The instructions for installing the Harden-Runner agent on your self-hosted VM runners are shown in the dashboard. To enable access to these instructions, please email support@stepsecurity.io. This agent is different than the one used for GitHub-hosted runners.

Features at a glance

For details, check out the documentation at https://docs.stepsecurity.io

View outbound network traffic at the job level

Applies to both GitHub-hosted and self-hosted runners

Harden-Runner monitors all outbound traffic from each job at the DNS and network layers

• After the workflow completes, each outbound call is correlated with each step of the job, and shown in the insights page

• For self-hosted runners, no changes are needed to workflow files to monitor egress traffic

• A filtering (block) egress policy is suggested in the insights page based on the current and past job runs

  

View outbound network traffic at the organization level

Applies to both GitHub-hosted and self-hosted runners

You can view all unique network destinations from all workflow runs in your organization on the Runtime Security tab.

• The All Observed Endpoints menu provides a detailed list of all network destinations contacted by your Actions runners.
• For each listed endpoint, the View Sample Workflow Runs option enables you to examine individual GitHub Actions workflow runs that interacted with the endpoint.

For more details refer Unified Network Egress View: Centralize GitHub Actions Network Destinations for Your Enterprise

View outbound HTTPS traffic at the job level

Applies to GitHub-hosted and self-hosted VM runners

Harden-Runner can monitor outbound HTTPS requests. This feature is supported with a commercial license.

• HTTPS events are monitored using eBPF (no MITM proxy is used)
• If a HTTP PUT/ POST/ PATCH call is made to GitHub APIs to a HTTP Path with a different organization than where the workflow is running, the call is marked as anomalous
• As of now, only HTTPS calls to github.com, api.github.com, *.pkg.github.com, and ghcr.io hosts are monitoried.

Detect anomalous outbound network traffic

Applies to both GitHub-hosted and self-hosted runners

You can detect suspicious/ anomalous traffic using this feature even in egress-policy:audit mode.

• Anomaly detection feature creates a machine learning model of outbound network calls by analyzing the historical data of the same workflow in previous runs
• After the baseline is created, any anomalous outbound destinations are marked as anomalous in the insights page, and real-time alerts are triggered
• You can view the list of all anomalous outbound network traffic in the Runtime detections page on the dashboard

For more details, refer to Anomalous Outbound Call Detection Using Machine Learning

Filter outbound network traffic to allowed endpoints

Applies to both GitHub-hosted and self-hosted runners

You can see recommended egress block policy in the Recommendations tab for each job. This is based on observed traffic across multiple runs of the job.

Once you set these allowed endpoints in the workflow file, or in the Policy Store and switch to using egress-policy:block

• Harden-Runner blocks egress traffic at the DNS (Layer 7) and network layers (Layers 3 and 4)
• It blocks DNS exfiltration, where attacker tries to send data out using DNS resolution
• Wildcard domains are supported, e.g. you can add *.data.mcr.microsoft.com:443 to the allowed list, and egress traffic will be allowed to eastus.data.mcr.microsoft.com:443 and westus.data.mcr.microsoft.com:443

Determine minimum GITHUB_TOKEN permissions using Harden-Runner

Applies to GitHub-hosted runners

Harden-Runner monitors outbound HTTPS requests using eBPF and uses the PATHs and VERBs of these HTTPS calls to recommend the minimum GITHUB_TOKEN permissions for each job in your workflow. This feature is supported with a commercial license.

• GITHUB_TOKEN is an automatically generated secret used to authenticate to GitHub APIs from GitHub Actions workflows.
• Harden-Runner can monitor the VERBs (e.g., GET, POST) and PATHs (e.g., /repos/owner/repo/issues) for calls made to the GitHub APIs from the runner.
• Each GitHub Actions API call requires a corresponding GITHUB_TOKEN permission. For instance, a GET request to the /repos/org/repo/info/refs?service=git-upload-pack endpoint requires the contents: read permission.
• The recommendation for the minimum GITHUB_TOKEN permissions are show in the Recommendations tab.

For more details, refer to Determine Minimum GITHUB_TOKEN Permissions Using eBPF with Harden-Runner.

View the name and path of every file written during the build process

Applies to both GitHub-hosted and self-hosted runners

View the name and path of every file that was written during the build process. This feature is supported with a commercial license.

• Harden-Runner tracks every file written to the GitHub Actions working directory during the build process.
• In the insights page in the File Write Events tab you can see a file explorer view of each file that was written to.
• Clicking on any file reveals a list of processes that wrote to it, providing complete transparency.

View process names and arguments

Applies to both GitHub-hosted and self-hosted runners

View process names, PIDs, and process arguments. This feature is supported with a commercial license.

• Harden-Runner tracks every process that is run during the build process.
• Clicking on any process ID (PID) in the network events, file events, or HTTPS events shows the process that caused the event, along with the process arguments.
• You can walk up the process tree by clicking View Parent Process to understand the build process and detect suspicious activity.

Detect tampering of source code during build

Applies to both GitHub-hosted and self-hosted runners

Harden-Runner monitors file writes and can detect if a file is overwritten.

• Source code overwrite is not expected in a release build
• All source code files are monitored, which means even changes to IaC files (Kubernetes manifest, Terraform) are detected
• You can enable notifications to get one-time alert when source code is overwritten
• For self-hosted runners, no changes are needed to workflow files for file monitoring

Run your job without sudo access

Applies to GitHub-hosted runners

GitHub-hosted runner uses passwordless sudo for running jobs.

• This means compromised build tools or dependencies can install attack tools

• If your job does not need sudo access, you see a policy recommendation to disable sudo in the insights page

• When you set disable-sudo to true, the job steps run without sudo access to the GitHub-hosted Ubuntu VM

  

Get real-time security alerts

Applies to both GitHub-hosted and self-hosted runners

Install the StepSecurity GitHub App to get security alerts/ notifications.

• Email, Slack, and Teams notifications are supported
• Notifications are sent when anomalous outbound network/ HTTPS traffic is detected, outbound traffic is blocked, or source code is overwritten
• Notifications are not repeated for the same alert for a given workflow

Discussions

• If you have questions or ideas, please use discussions.
• For support for self-hosted runners and private repositories, email support@stepsecurity.io.
• If you use a different CI/CD Provider (e.g. Jenkins, Gitlab CI, etc), and would like to use Harden Runner in your environment, please email interest@stepsecurity.io

How does it work?

GitHub-Hosted Runners

For GitHub-hosted runners, Harden-Runner GitHub Action downloads and installs the StepSecurity Agent.

• The code to monitor file, process, and network activity is in the Agent.
• The agent is written in Go and is open source at https://github.com/step-security/agent
• The agent's build is reproducible. You can view the steps to reproduce the build here

Self-Hosted Actions Runner Controller (ARC) Runners

• ARC Harden Runner daemonset uses eBPF
• You can find more details in this blog post: https://www.stepsecurity.io/blog/introducing-harden-runner-for-kubernetes-based-self-hosted-actions-runners
• ARC Harden Runner is NOT open source.

Self-Hosted VM Runners (e.g. on EC2)

• For self-hosted VMs, you add the Harden-Runner agent into your runner image (e.g. AMI).
• Agent for self-hosted VMs is NOT open source.

Limitations

GitHub-Hosted Runners

1. Only Ubuntu VM is supported. Windows and MacOS GitHub-hosted runners are not supported. There is a discussion about that here.
2. Harden-Runner is not supported when job is run in a container as it needs sudo access on the Ubuntu VM to run. It can be used to monitor jobs that use containers to run steps. The limitation is if the entire job is run in a container. That is not common for GitHub Actions workflows, as most of them run directly on ubuntu-latest. Note: This is not a limitation for Self-Hosted runners.

Self-Hosted Actions Runner Controller (ARC) Runners

1. Since ARC Harden Runner uses eBPF, only Linux jobs are supported. Windows and MacOS jobs are not supported.

Self-Hosted VM Runners (e.g. on EC2)

1. Only Ubuntu VM is supported. Windows and MacOS jobs are not supported.