- Usage of Shell executor
- Usage of Docker executor
- Usage of private Docker images with
- Systems with Docker installed
- Usage of SSH executor
- Usage of Parallels executor
- Cloning a runner
- Network Segmentation
When using GitLab Runner you should be aware of potential security implications when running your jobs.
Generally, it’s unsafe to run tests with
shell executors. The jobs are run
with user’s permissions (the GitLab Runner permissions) and can steal code from other
projects that are run on this server. Use only it for running the trusted builds.
Docker can be considered safe when running in non-privileged mode. To make
such setup more secure it’s advised to run jobs as a user (non-root) in Docker
containers with disabled sudo or dropped
On the other hand, there’s a privileged mode which enables full access to the host system, permission to mount and unmount volumes, and run nested containers. It’s not advised to run containers in privileged mode.
More granular permissions can be configured in non-privileged mode via the
When using the private Docker images support described in
advanced configuration: using a private container registry
you should use
always as the
pull_policy value. Especially you should
always pull policy if you are hosting a public, shared Runner with the
Docker or Kubernetes executors.
Let’s consider an example where the pull policy is set to
- User A has a private image at
- User A starts a build on a shared runner: The build receives the registry credentials and pulls the image after authorization in registry.
- The image is stored on a shared runner’s host.
- User B doesn’t have access to the private image at
- User B starts a build that is using this image on the same shared runner as User A: Runner finds a local version of the image and uses it even if the image could not be pulled because of missing credentials.
Therefore, if you host a runner that can be used by different users and
different projects (with mixed private, and public access levels) you should
if-not-present as the pull policy value, but use:
never- If you want to limit users to use the only image pre-downloaded by you.
always- If you want to give users the possibility to download any image from any registry.
if-not-present pull policy should be used only for specific runners
used by trusted builds and users.
Read the pull policies documentation for more information.
When installing the package on Linux systems with Docker installed,
gitlab-runner will create a user that will have permission to access the
daemon. This makes the jobs that run with the
shell executor able to access
with full permissions and potentially allows root access to the server.
SSH executors are susceptible to MITM attack (man-in-the-middle), because of
StrictHostKeyChecking option. This will be fixed in one of the future
Parallels executor is the safest possible option because it uses full system virtualization and with VM machines that are configured to run in the isolated virtualization and VM machines that are configured to run in isolated mode. It blocks access to all peripherals and shared folders.
Runners use a token to identify to the GitLab Server. If you clone a runner then the cloned runner could be picking up the same jobs for that token. This is a possible attack vector to “steal” runner jobs.
GitLab Runner is designed to run user-controlled scripts. To reduce the attack surface if a job is malicious, you can consider running them in their own network segment. This would provide network separation from other infrastructure and services.
All needs are unique, but for a cloud environment, this could include:
- Configuring runner virtual machines in their own network segment
- Blocking SSH access from the Internet to runner virtual machines
- Restricting traffic between runner virtual machines
- Filtering access to cloud provider metadata endpoints