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Hardening your instance

Here are some suggestions which improve the security of parts of your Pleroma instance.

Configuration file

These changes should go into prod.secret.exs or dev.secret.exs, depending on your MIX_ENV value.

http

Recommended value: [ip: {127, 0, 0, 1}]

This sets the Pleroma application server to only listen to the localhost interface. This way, you can only reach your server over the Internet by going through the reverse proxy. By default, Pleroma listens on all interfaces.

Recommended value: true

This sets the secure flag on Pleroma’s session cookie. This makes sure, that the cookie is only accepted over encrypted HTTPs connections. This implicitly renames the cookie from pleroma_key to __Host-pleroma-key which enforces some restrictions. (see cookie prefixes)

:http_security

Recommended value: true

This will send additional HTTP security headers to the clients, including:

  • X-XSS-Protection: "1; mode=block"
  • X-Permitted-Cross-Domain-Policies: "none"
  • X-Frame-Options: "DENY"
  • X-Content-Type-Options: "nosniff"
  • X-Download-Options: "noopen"

A content security policy (CSP) will also be set:

content-security-policy:
  default-src 'none';
  base-uri 'self';
  frame-ancestors 'none';
  img-src 'self' data: https:;
  media-src 'self' https:;
  style-src 'self' 'unsafe-inline';
  font-src 'self';
  script-src 'self';
  connect-src 'self' wss://example.tld;
  manifest-src 'self';
  upgrade-insecure-requests;

sts

Recommended value: true

An additional “Strict transport security” header will be sent with the configured sts_max_age parameter. This tells the browser, that the domain should only be accessed over a secure HTTPs connection.

ct_max_age

An additional “Expect-CT” header will be sent with the configured ct_max_age parameter. This enforces the use of TLS certificates that are published in the certificate transparency log. (see Expect-CT)

referrer_policy

Recommended value: same-origin

If you click on a link, your browser’s request to the other site will include from where it is coming from. The “Referrer policy” header tells the browser how and if it should send this information. (see Referrer policy)

systemd

A systemd unit example is provided at installation/pleroma.service.

PrivateTmp

Recommended value: true

Use private /tmp and /var/tmp folders inside a new file system namespace, which are discarded after the process stops.

ProtectHome

Recommended value: true

The /home, /root, and /run/user folders can not be accessed by this service anymore. If your Pleroma user has its home folder in one of the restricted places, or use one of these folders as its working directory, you have to set this to false.

ProtectSystem

Recommended value: full

Mount /usr, /boot, and /etc as read-only for processes invoked by this service.

PrivateDevices

Recommended value: true

Sets up a new /dev mount for the process and only adds API pseudo devices like /dev/null, /dev/zero or /dev/random but not physical devices. This may not work on devices like the Raspberry Pi, where you need to set this to false.

NoNewPrivileges

Recommended value: true

Ensures that the service process and all its children can never gain new privileges through execve().

CapabilityBoundingSet

Recommended value: ~CAP_SYS_ADMIN

Drops the sysadmin capability from the daemon.