Harden-Runner
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Corporate laptops and production servers have strong security monitoring for compliance and risk reduction. However, CI/CD runners, which handle sensitive data like cloud secrets and production builds, often lack such protections, making them targets for supply chain attacks like SolarWinds and Codecov.
Traditional security tools struggle with CI/CD runners due to their short-lived nature and lack of workflow context.
Harden-Runner fills this gap by providing tailored security monitoring, ensuring CI/CD runners receive the same protection as other critical systems.
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Compromised workflows, dependencies, and build tools pose two major threats:
Exfiltration of CI/CD credentials and source code
Tampering of source code, dependencies, or artifacts during the build process to inject backdoors
To mitigate these risks, Harden-Runner provides key security measures. The table below outlines its core functionalities and the threats they help prevent:
Network Traffic Control
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
Source Code Integrity Check
Detect if source code is being tampered during the build process to inject a backdoor
Dependency and Workflow Monitoring
Detect poisoned workflows and compromised dependencies that exhibit suspicious behavior
GitHub Token Permission Enforcement
Determine minimum GITHUB_TOKEN permissions by monitoring HTTPS calls to GitHub APIs
Securing your CI/CD pipelines requires configuring your runners with StepSecurity’s Harden-Runner, which provides comprehensive monitoring and protection across different runner environments.
Harden-Runner supports multiple CI/CD runner types:
✅ Full support
Add Harden-Runner Action to workflow
Yes
✅ Full support
Include agent in runner image
No
✅ Full support
Install agent as a service
No
✅ Full support
Deploy as DaemonSet
No
✅ Full support
Pre-integrated
No
Step 2: You will see a link to security insights and recommendations in the workflow logs and the job markdown summary.
Step 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 use the Policy Store to apply the policy without modifying the workflow file. From now on, any outbound calls not on the allowed list will be blocked.
To enable runtime security for self-hosted runners on Cloud VMs (e.g. EC2 instances), you can add the Harden-Runner agent to your runner image.
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 must add the Harden-Runner GitHub Action to jobs where you want to enable block mode.
You can access security insights and runtime detections under the Harden-Runner section in your dashboard.
Self-hosted bare-metal runners are set up by installing the harden-runner agent as a service. This setup closely resembles the self-hosted cloud VM scenario but runs directly on physical hardware instead of virtualized environments.
Actions Runner Controller (ARC) is a Kubernetes operator that orchestrates and scales self-hosted runners for GitHub Actions.
Rather than incorporating the Harden Runner GitHub Action into each individual workflow, 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 need to add the Harden-Runner GitHub Action to jobs where you want to enable block mode.
You can access security insights and runtime detections under the Runtime Security tab in your dashboard.
For each GitHub Actions workflow run, Harden-Runner monitors the run-time network, file, and process events and makes runtime insights available via the StepSecurity Web App.
There are four ways to find the insights link:
Step 1: Navigate to build log of your workflow file in Github Actions.
Step 3: Once you click on the Insights link, you will be redirected to the Summary tab in the StepSecurity Web App. The Summary Page provides an overview of:
Outbound destinations contacted during the job execution.
HTTPS requests and the number of actions taken.
Detections (if any security risks were found).
StepSecurity provides a dashboard where you can view the latest GitHub Actions workflow runs monitored by Harden-Runner. This guide will help you navigate the dashboard and access insights for specific workflow runs.
Step 1: Navigate to https://app.stepsecurity.io/github/<GITHUB_ORG_NAME>/actions/dashboard
Step 2: In the left-hand menu, under Harden-Runner, click Workflow Runs
Step 3: After opening the Workflow Runs page, locate the workflow you want to inspect and click on it.
Step 4: Once inside the workflow details page, navigate to the Summary tab.
Here, you can review:
Outbound destinations contacted during the workflow.
Security detections (if any were found).
Actions performed by the workflow.
Step 1: Navigate to the workflow run page
Step 2: Click "📄 View Full Report"
Step 3: Review the outbound connections allowed during the workflow execution.
Step 1: Navigate to the Pull Request
Step 2: View Check Details
Look at the checks summary under your pull request.
Identify any failed or successful checks.
Click on the “Details” link next to the StepSecurity Harden-Runner check.
Step 3: Access Insights URL
On the new page, select StepSecurity Harden-Runner from the list of workflow checks.
Find the Insights URL under the Workflow Run Insights section.
Click the Insights URL to proceed.
Step 4: Review Security Insights
The Insights page will display outbound traffic details, network events, and security findings.
Verify if any unauthorized outbound connections were detected.
Review the All Outbound Destinations and All Detections sections for further analysis.
To prevent the scenario
To detect the and scenarios
To detect and scenarios
To set to reduce the impact of exfiltration
Step 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 using .
Step 3: Click on the link (). You will see a process monitor view of network and file events correlated with each step of the job.
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 a packer or as a post-install step when using the project to set up runners.
Step 2: Look for the Harden-Runner step in the log and click on the Insights link which appears in the logs as View security insights and recommended policy at: followed by a clickable URL (this is an ).
To enable GitHub Checks, check out this .
