The basic github environment structure of a big **company** is to own an **enterprise** which owns **several organizations** and each of them may contain **several repositories** and **several teams.**. Smaller companies may just **own one organization and no enterprises**.
From a user point of view a **user** can be a **member** of **different enterprises and organizations**. Within them the user may have **different enterprise, organization and repository roles**.
And finally **repositories may have special protection mechanisms**.
## Privileges
### Enterprise Roles
* **Enterprise owner**: People with this role can **manage administrators, manage organizations within the enterprise, manage enterprise settings, enforce policy across organizations**. However, they **cannot access organization settings or content** unless they are made an organization owner or given direct access to an organization-owned repository
* **Enterprise members**: Members of organizations owned by your enterprise are also **automatically members of the enterprise**.
### Organization Roles
In an organisation users can have different roles:
* **Organization owners**: Organization owners have **complete administrative access to your organization**. This role should be limited, but to no less than two people, in your organization.
* **Organization members**: The **default**, non-administrative role for **people in an organization** is the organization member. By default, organization members **have a number of permissions**.
* **Billing managers**: Billing managers are users who can **manage the billing settings for your organization**, such as payment information.
* **Security Managers**: It's a role that organization owners can assign to any team in an organization. When applied, it gives every member of the team permissions to **manage security alerts and settings across your organization, as well as read permissions for all repositories** in the organization.
* If your organization has a security team, you can use the security manager role to give members of the team the least access they need to the organization.
* **Github App managers**: To allow additional users to **manage GitHub Apps owned by an organization**, an owner can grant them GitHub App manager permissions.
* **Outside collaborators**: An outside collaborator is a person who has **access to one or more organization repositories but is not explicitly a member** of the organization.
You can **compare the permissions** of these roles in this table: [https://docs.github.com/en/organizations/managing-peoples-access-to-your-organization-with-roles/roles-in-an-organization#permissions-for-organization-roles](https://docs.github.com/en/organizations/managing-peoples-access-to-your-organization-with-roles/roles-in-an-organization#permissions-for-organization-roles)
### Members Privileges
In _https://github.com/organizations/\<org\_name>/settings/member\_privileges_ you can see the **permissions users will have just for being part of the organisation**.
The settings here configured will indicate the following permissions of members of the organisation:
* Be admin, writer, reader or no permission over all the organisation repos.
* If members can create private, internal or public repositories.
* If forking of repositories is possible
* If it's possible to invite outside collaborators
* If public or private sites can be published
* The permissions admins has over the repositories
* **Read**: Recommended for **non-code contributors** who want to view or discuss your project
* **Triage**: Recommended for **contributors who need to proactively manage issues and pull requests** without write access
* **Write**: Recommended for contributors who **actively push to your project**
* **Maintain**: Recommended for **project managers who need to manage the repository** without access to sensitive or destructive actions
* **Admin**: Recommended for people who need **full access to the project**, including sensitive and destructive actions like managing security or deleting a repository
You can **compare the permissions** of each role in this table [https://docs.github.com/en/organizations/managing-access-to-your-organizations-repositories/repository-roles-for-an-organization#permissions-for-each-role](https://docs.github.com/en/organizations/managing-access-to-your-organizations-repositories/repository-roles-for-an-organization#permissions-for-each-role)
You can **list the teams created in an organization** in _https://github.com/orgs/\<org\_name>/teams_. Note that to see the teams which are children of other teams you need to access each parent team.
Github offers different ways to authenticate to your account and perform actions on your behalf.
### Web Access
Accessing **github.com** you can login using your **username and password** (and a **2FA potentially**).
### **SSH Keys**
You can configure your account with one or several public keys allowing the related **private key to perform actions on your behalf.** [https://github.com/settings/keys](https://github.com/settings/keys)
#### **GPG Keys**
You **cannot impersonate the user with these keys** but if you don't use it it might be possible that you **get discover for sending commits without a signature**. Learn more about [vigilant mode here](https://docs.github.com/en/authentication/managing-commit-signature-verification/displaying-verification-statuses-for-all-of-your-commits#about-vigilant-mode).
### **Personal Access Tokens**
You can generate personal access token to **give an application access to your account**. When creating a personal access token the **user** needs to **specify** the **permissions** to **token** will have. [https://github.com/settings/tokens](https://github.com/settings/tokens)
### Oauth Applications
Oauth applications may ask you for permissions **to access part of your github information or to impersonate you** to perform some actions. A common example of this functionality is the **login with github button** you might find in some platforms.
* You can **create** your own **Oauth applications** in [https://github.com/settings/developers](https://github.com/settings/developers)
* You can see all the **Oauth applications that has access to your account** in [https://github.com/settings/applications](https://github.com/settings/applications)
* You can see the **scopes that Oauth Apps can ask for** in [https://docs.github.com/en/developers/apps/building-oauth-apps/scopes-for-oauth-apps](https://docs.github.com/en/developers/apps/building-oauth-apps/scopes-for-oauth-apps)
* You can see third party access of applications in an **organization** in _https://github.com/organizations/\<org\_name>/settings/oauth\_application\_policy_
* An **OAuth App** should always **act as the authenticated GitHub user across all of GitHub** (for example, when providing user notifications) and with access only to the specified scopes..
* An OAuth App can be used as an identity provider by enabling a "Login with GitHub" for the authenticated user.
* **Don't** build an **OAuth App** if you want your application to act on a **single repository**. With the `repo` OAuth scope, OAuth Apps can **act on \_all**\_\*\* of the authenticated user's repositorie\*\*s.
* **Don't** build an OAuth App to act as an application for your **team or company**. OAuth Apps authenticate as a **single user**, so if one person creates an OAuth App for a company to use, and then they leave the company, no one else will have access to it.
* **More** in [here](https://docs.github.com/en/developers/apps/getting-started-with-apps/about-apps#about-oauth-apps).
### Github Applications
Github applications can ask for permissions to **access your github information or impersonate you** to perform specific actions over specific resources. In Github Apps you need to specify the repositories the app will have access to.
* To install a GitHub App, you must be an **organisation owner or have admin permissions** in a repository.
* The GitHub App should **connect to a personal account or an organisation**.
* You can create your own Github application in [https://github.com/settings/apps](https://github.com/settings/apps)
* You can see all the **Github applications that has access to your account** in [https://github.com/settings/apps/authorizations](https://github.com/settings/apps/authorizations)
* These are the **API Endpoints for Github Applications** [https://docs.github.com/en/rest/overview/endpoints-available-for-github-app](https://docs.github.com/en/rest/overview/endpoints-available-for-github-apps). Depending on the permissions of the App it will be able to access some of them
* A GitHub App should **take actions independent of a user** (unless the app is using a [user-to-server](https://docs.github.com/en/apps/building-github-apps/identifying-and-authorizing-users-for-github-apps#user-to-server-requests) token). To keep user-to-server access tokens more secure, you can use access tokens that will expire after 8 hours, and a refresh token that can be exchanged for a new access token. For more information, see "[Refreshing user-to-server access tokens](https://docs.github.com/en/apps/building-github-apps/refreshing-user-to-server-access-tokens)."
* Make sure the GitHub App integrates with **specific repositories**.
* The GitHub App should **connect to a personal account or an organisation**.
* Don't expect the GitHub App to know and do everything a user can.
* **Don't use a GitHub App if you just need a "Login with GitHub" service**. But a GitHub App can use a [user identification flow](https://docs.github.com/en/apps/building-github-apps/identifying-and-authorizing-users-for-github-apps) to log users in _and_ do other things.
* Don't build a GitHub App if you _only_ want to act as a GitHub user and do everything that user can do.
* If you are using your app with GitHub Actions and want to modify workflow files, you must authenticate on behalf of the user with an OAuth token that includes the `workflow` scope. The user must have admin or write permission to the repository that contains the workflow file. For more information, see "[Understanding scopes for OAuth apps](https://docs.github.com/en/apps/building-oauth-apps/understanding-scopes-for-oauth-apps/#available-scopes)."
* **More** in [here](https://docs.github.com/en/developers/apps/getting-started-with-apps/about-apps#about-github-apps).
This **isn't a way to authenticate in github**, but a **malicious** Github Action could get **unauthorised access to github** and **depending** on the **privileges** given to the Action several **different attacks** could be done. See below for more information.
Git actions allows to automate the **execution of code when an event happen**. Usually the code executed is **somehow related to the code of the repository** (maybe build a docker container or check that the PR doesn't contain secrets).
### Configuration
In _https://github.com/organizations/\<org\_name>/settings/actions_ it's possible to check the **configuration of the github actions** for the organization.
It's possible to disallow the use of github actions completely, **allow all github actions**, or just allow certain actions.
It's also possible to configure **who needs approval to run a Github Action** and the **permissions of the \_GITHUB\_TOKEN**\_\*\* of a Github Action when it's run\*\*.
Github Action usually need some kind of secrets to interact with github or third party applications. To **avoid putting them in clear-text** in the repo, github allow to put them as **Secrets**.
These secrets can be configured **for the repo or for all the organization**. Then, in order for the **Action to be able to access the secret** you need to declare it like:
```yaml
steps:
- name: Hello world action
with: # Set the secret as an input
super_secret: ${{ secrets.SuperSecret }}
env: # Or as an environment variable
super_secret: ${{ secrets.SuperSecret }}
```
#### Example using Bash <a href="#example-using-bash" id="example-using-bash"></a>
```yaml
steps:
- shell: bash
env:
SUPER_SECRET: ${{ secrets.SuperSecret }}
run: |
example-command "$SUPER_SECRET"
```
{% hint style="warning" %}
Secrets **can only be accessed from the Github Actions** that have them declared.
Once configured in the repo or the organizations **users of github won't be able to access them again**, they just will be able to **change them**.
{% endhint %}
Therefore, the **only way to steal github secrets is to be able to access the machine that is executing the Github Action** (in that scenario you will be able to access only the secrets declared for the Action).
Github allows to create **environments** where you can save **secrets**. Then, you can give the github action access to the secrets inside the environment with something like:
```yaml
jobs:
deployment:
runs-on: ubuntu-latest
environment: env_name
```
You can configure an environment to be **accessed** by **all branches** (default), **only protected** branches or **specify** which branches can access it.
A Github Action can be **executed inside the github environment** or can be executed in a **third party infrastructure** configured by the user.
Several organizations will allow to run Github Actions in a **third party infrastructure** as it use to be **cheaper**.
You can **list the self-hosted runners** of an organization in _https://github.com/organizations/\<org\_name>/settings/actions/runners_
The way to find which **Github Actions are being executed in non-github infrastructure** is to search for `runs-on: self-hosted` in the Github Action configuration yaml.
It's **not possible to run a Github Action of an organization inside a self hosted box** of a different organization because **a unique token is generated for the Runner** when configuring it to know where the runner belongs.
If the custom **Github Runner is configured in a machine inside AWS or GCP** for example, the Action **could have access to the metadata endpoint** and **steal the token of the service account** the machine is running with.
### Git Action Compromise
If all actions (or a malicious action) are allowed a user could use a **Github action** that is **malicious** and will **compromise** the **container** where it's being executed.
{% hint style="danger" %}
A **malicious Github Action** run could be **abused** by the attacker to:
* **Steal all the secrets** the Action has access to
* **Move laterally** if the Action is executed inside a **third party infrastructure** where the SA token used to run the machine can be accessed (probably via the metadata service)
* **Abuse the token** used by the **workflow** to **steal the code of the repo** where the Action is executed or **even modify it**.
Branch protections are designed to **not give complete control of a repository** to the users. The goal is to **put several protection methods before being able to write code inside some branch**.
The **branch protections of a repository** can be found in _https://github.com/\<orgname>/\<reponame>/settings/branches_
{% hint style="info" %}
It's **not possible to set a branch protection at organization level**. So all of them must be declared on each repo.
{% endhint %}
Different protections can be applied to a branch (like to master):
* You can **require a PR before merging** (so you cannot directly merge code over the branch). If this is select different other protections can be in place:
* **Require a number of approvals**. It's very common to require 1 or 2 more people to approve your PR so a single user isn't capable of merge code directly.
* **Dismiss approvals when new commits are pushed**. If not, a user may approve legit code and then the user could add malicious code and merge it.
* **Require reviews from Code Owners**. At least 1 code owner of the repo needs to approve the PR (so "random" users cannot approve it)
* **Restrict who can dismiss pull request reviews.** You can specify people or teams allowed to dismiss pull request reviews.
* **Allow specified actors to bypass pull request requirements**. These users will be able to bypass previous restrictions.
* **Require status checks to pass before merging.** Some checks needs to pass before being able to merge the commit (like a github action checking there isn't any cleartext secret).
* **Require conversation resolution before merging**. All comments on the code needs to be resolved before the PR can be merged.
* **Require signed commits**. The commits need to be signed.
* **Require linear history.** Prevent merge commits from being pushed to matching branches.
* **Include administrators**. If this isn't set, admins can bypass the restrictions.
* **Restrict who can push to matching branches**. Restrict who can send a PR.
{% hint style="info" %}
As you can see, even if you managed to obtain some credentials of a user, **repos might be protected avoiding you to pushing code to master** for example to compromise the CI/CD pipeline.
