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Hardening - Configuration Recommendations

General hardening guidelines are outlined in the main hardening documentation.

Some hardening recommendations for GitLab instances involve additional services or control through configuration files. As a reminder, any time you are making changes to configuration files, make backup copies of them before editing. Additionally, if you are making a lot of changes it is recommended you do not do all of the changes at once, and test them after each change to ensure everything is working.

NGINX

NGINX is used to serve up the web interface used to access the GitLab instance. As NGINX is controlled and integrated into GitLab, modification of the /etc/gitlab/gitlab.rb file used for adjustments. Here are a few recommendations for helping to improve the security of NGINX itself:

  1. Create the Diffie-Hellman key:

    sudo openssl dhparam -out /etc/gitlab/ssl/dhparam.pem 4096

  2. Edit /etc/gitlab/gitlab.rb and add the following:

    #
# Only strong ciphers are used
#
nginx['ssl_ciphers'] = "ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:TLS_AES_256_GCM_SHA384:TLS_AES_128_GCM_SHA256"
#
# Follow preferred ciphers and the order listed as preference
#
nginx['ssl_prefer_server_ciphers'] = "on"
#
# Only allow TLSv1.2 and TLSv1.3
#
nginx['ssl_protocols'] = "TLSv1.2 TLSv1.3"

##! **Recommended in: https://nginx.org/en/docs/http/ngx_http_ssl_module.html**
nginx['ssl_session_cache'] = "builtin:1000  shared:SSL:10m"

##! **Default according to https://nginx.org/en/docs/http/ngx_http_ssl_module.html**
nginx['ssl_session_timeout'] = "5m"

# Should prevent logjam attack etc
nginx['ssl_dhparam'] = "/etc/gitlab/ssl/dhparam.pem" # changed from nil

# Turn off session ticket reuse
nginx['ssl_session_tickets'] = "off"
# Pick our own curve instead of what openssl hands us
nginx['ssl_ecdh_curve'] = "secp384r1"

  3. Reconfigure GitLab:

    sudo gitlab-ctl reconfigure

Consul

Consul can be integrated into a GitLab environment, and is intended for larger deployments. In general for self-managed and standalone deployments with less than 1000 users, Consul may not be needed. If it is needed, first review the documentation on Consul, but more importantly ensure that encryption is used during communications. For more detailed information on Consul visit the HashiCorp website to understand how it works, and review the information on encryption security.

Environment Variables

You can customize multiple environment variables on self-managed systems. The main environment variable to take advantage of from a security perspective is GITLAB_ROOT_PASSWORD during the installation process. If you are installing the self-managed system with a public-facing IP address exposed to the Internet, make sure the password is set to something strong. Historically, setting up any type of public-facing service - whether it is GitLab or some other application - has shown that opportunistic attacks occur as soon as those systems are discovered, so the hardening process should start during the installation process.

As mentioned in the operating system recommendations ideally there should be firewall rules already in place before the GitLab installation begins, but you should still set a secure password before the installation through GITLAB_ROOT_PASSWORD.

Git Protocols

To ensure that only authorized users are using SSH for Git access, add the following to your /etc/ssh/sshd_config file:

# Ensure only authorized users are using Git
AcceptEnv GIT_PROTOCOL

This ensures that users cannot pull down projects using SSH unless they have a valid GitLab account that can perform git operations over SSH. More details can be found under Configuring Git Protocol.

Incoming Email

You can configure a GitLab self-managed instance to allow for incoming email to be used for commenting or creating issues and merge requests by registered users on the GitLab instance. In a hardened environment you should not configure this feature as it involves outside communications sending in information.

If the feature is required, follow the instructions in the incoming email documentation, with the following recommendations to ensure maximum security:

Redis Replication and Failover

Redis is used on a Linux package installation for replication and failover, and can be set up when scaling requires that capability. Bear in mind that this opens TCP ports 6379 for Redis and 26379 for Sentinel. Follow the replication and failover documentation but note the IP addresses of all of the nodes, and set up firewall rules between nodes that only allow the other node to access those particular ports.

Sidekiq Configuration

In the instructions for configuring an external Sidekiq there are numerous references to configuring IP ranges. You must configure HTTPS, and consider restricting those IP addresses to specific systems that Sidekiq talks to. You might have to adjust firewall rules at the operating system level as well.

S/MIME Signing of Email

If the GitLab instance is configured for sending out email notifications to users, configure S/MIME signing to help the recipients ensure that the emails are legitimate. Follow the instructions on signing outgoing email.

Container registry

If Lets Encrypt is configured, the container registry is enabled by default. This allows projects to store their own Docker images. Follow the instructions for configuring the container registry, so you can do things like restrict automatic enablement on new projects and disabling the container registry entirely. You may have to adjust firewall rules to allow access - if a completely standalone system, you should restrict access to the Container Registry to localhost only. Specific examples of ports used and their configuration are also included in the documentation.