Implement Sha_pinning_required Check In Allowed Actions Policy

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This article discusses the implementation of a new sha_pinning_required check within the allowed_actions policy for GitHub Actions. This enhancement aims to improve security by ensuring that specific actions are pinned to a particular SHA, preventing potential vulnerabilities from malicious updates. We will delve into the technical details, covering the necessary modifications to the policy structure, code implementation, and documentation updates.

Understanding the Need for sha_pinning_required

In the realm of GitHub Actions security, ensuring the integrity and authenticity of workflows is paramount. One crucial aspect is controlling which actions are permitted to run within a repository or organization. The allowed_actions policy serves this purpose by defining a set of approved actions. However, simply allowing an action by name or tag can still leave room for risk. If an action's maintainer introduces a malicious update, workflows using the action could be compromised. This is where SHA pinning comes in. SHA pinning involves specifying the exact commit SHA of an action, guaranteeing that the workflow always uses the intended version and mitigating the risk of malicious updates. The sha_pinning_required check will enforce this practice, adding a significant layer of security.

GitHub API Enhancements

Recent updates to the GitHub API have introduced a new setting, sha_pinning_required, in the responses for permissions related to GitHub Actions. Specifically, the following API endpoints now include this setting:

  • GET /orgs/{org}/actions/permissions
  • GET /repos/{owner}/{repo}/actions/permissions

These endpoints provide information about the allowed actions and other settings for organizations and repositories, respectively. The sha_pinning_required field, which can be either true or false, indicates whether SHA pinning is enforced for the given context. This enhancement provides the necessary information to implement the policy check effectively.

Example API Responses

Let's examine example responses from these API endpoints to illustrate the sha_pinning_required setting:

For GET /orgs/{org}/actions/permissions:

{
  "enabled_repositories": "all",
  "allowed_actions": "selected",
  "selected_actions_url": "https://api.github.com/organizations/42/actions/permissions/selected-actions",
  "sha_pinning_required": true
}

This response indicates that for the organization with ID 42, all repositories are enabled for GitHub Actions, the allowed_actions policy is set to selected, and, crucially, sha_pinning_required is set to true. This means that any actions used within this organization must be pinned to a specific SHA.

For GET /repos/{owner}/{repo}/actions/permissions:

{
  "enabled": true,
  "allowed_actions": "selected",
  "selected_actions_url": "https://api.github.com/repositories/42/actions/permissions/selected-actions",
  "sha_pinning_required": true
}

Similarly, this response shows that for the repository with ID 42, GitHub Actions are enabled, the allowed_actions policy is selected, and sha_pinning_required is true. This enforces SHA pinning for actions used within this repository.

Implementing the sha_pinning_required Check

The implementation of the sha_pinning_required check involves several key steps, including updating the policy structure, modifying the code to perform the check, and updating the relevant documentation. Let's explore each of these steps in detail.

Policy Updates

The first step is to incorporate the sha_pinning_required setting into the policy definitions. This involves modifying the YAML schema used to define the allowed_actions policy at both the repository and organization levels.

Repository Policy

In the repository-level policy (typically defined in a repository.yml file), the sha_pinning_required setting needs to be added under the allowed_actions section. This allows administrators to specify whether SHA pinning is enforced for actions used within the repository.

Example Repository Policy Snippet:

allowed_actions:
  sha_pinning_required: true
  # Other allowed_actions settings

This snippet demonstrates how the sha_pinning_required setting can be added to the allowed_actions policy. When set to true, this enforces SHA pinning for all actions used in the repository.

Organization Policy

At the organization level, the policy needs to be extended to include a section for actions. This section will encompass all the checks returned by the GET /orgs/{org}/actions/permissions API endpoint, including the sha_pinning_required setting. This allows organization administrators to enforce SHA pinning across all repositories within the organization.

Example Organization Policy Snippet:

actions:
  sha_pinning_required: true
  enabled_repositories: all
  allowed_actions: selected
  selected_actions_url: "https://api.github.com/organizations/42/actions/permissions/selected-actions"

This snippet illustrates how the actions section can be added to the organization policy, including the sha_pinning_required setting and other relevant information returned by the GitHub API.

Code Implementation

With the policy structure updated, the next step is to modify the code to actually perform the sha_pinning_required check. This involves retrieving the policy settings, querying the GitHub API to obtain the current sha_pinning_required status, and comparing the two to ensure compliance.

Checking for sha_pinning_required

The code needs to be updated to check the sha_pinning_required setting in both the repository and organization policies. This involves reading the policy files, extracting the setting, and then using the GitHub API to determine the current status of SHA pinning. If the policy requires SHA pinning and the action being used is not pinned to a specific SHA, the check should fail, preventing the workflow from running.

Pseudo-code Example:

def check_sha_pinning_required(repository, action):
  # Get repository policy
  repo_policy = get_repository_policy(repository)
  # Get organization policy
  org_policy = get_organization_policy(repository.organization)

  # Check repository policy
  if repo_policy and repo_policy.allowed_actions and repo_policy.allowed_actions.sha_pinning_required:
    if not is_action_pinned(action):
      return False

  # Check organization policy
  if org_policy and org_policy.actions and org_policy.actions.sha_pinning_required:
    if not is_action_pinned(action):
      return False

  return True

This pseudo-code demonstrates the basic logic for checking the sha_pinning_required setting. It retrieves the repository and organization policies, checks if SHA pinning is required, and then verifies whether the action being used is pinned to a specific SHA. If SHA pinning is required and the action is not pinned, the function returns False, indicating a failure.

Documentation Updates

Finally, it's crucial to update the documentation to reflect the new sha_pinning_required check and how to use it. This includes updating the README file and any other relevant documentation to explain the purpose of the check, how to configure it, and the implications of enforcing SHA pinning.

Updating the README

The README file should be updated to include a section on the sha_pinning_required check. This section should explain what SHA pinning is, why it's important, and how to configure the sha_pinning_required setting in the repository and organization policies. It should also provide examples of how to pin actions to specific SHAs in workflows.

Example README Snippet:

### SHA Pinning Required

The `sha_pinning_required` setting enforces SHA pinning for actions used in your repository or organization. SHA pinning ensures that workflows always use the intended version of an action, mitigating the risk of malicious updates.

To enable SHA pinning, set `sha_pinning_required` to `true` in your repository or organization policy:

```yaml
allowed_actions:
  sha_pinning_required: true


This snippet demonstrates how the README file can be updated to explain the `sha_pinning_required` check and how to configure it.

## Conclusion

Implementing the `sha_pinning_required` check in the `allowed_actions` policy is a significant step towards enhancing the security of GitHub Actions workflows. By enforcing SHA pinning, we can mitigate the risk of malicious updates and ensure the integrity of our workflows. This article has outlined the technical details of this implementation, covering the necessary policy updates, code modifications, and documentation changes. By following these steps, we can effectively integrate the `sha_pinning_required` check into our GitHub Actions security framework and safeguard our workflows against potential threats. This enhancement contributes to a more secure and reliable CI/CD pipeline, fostering trust and confidence in our software development processes. **_By enforcing SHA pinning_**, organizations and repositories can maintain greater control over the actions used in their workflows, reducing the attack surface and promoting a more secure development environment. **_This proactive approach to security_** is essential for protecting sensitive data and maintaining the integrity of software projects. The `sha_pinning_required` check is a valuable tool for achieving these goals and ensuring the long-term security of GitHub Actions workflows.