mjolnir

A moderation tool for Matrix. Visit #mjolnir:matrix.org for more information.

Features

As an all-in-one moderation tool, it can protect your server from malicious invites, spam messages, and whatever else you don't want. In addition to server-level protection, Mjolnir is great for communities wanting to protect their rooms without having to use their personal accounts for moderation.

The bot by default includes support for bans, redactions, anti-spam, server ACLs, room directory changes, room alias transfers, account deactivation, room shutdown, and more.

A Synapse module is also available to apply the same rulesets the bot uses across an entire homeserver.

Bot configuration

It is recommended to use Pantalaimon so your management room can be encrypted. This also applies if you are looking to moderate an encrypted room.

If you aren't using encrypted rooms anywhere, get an access token by opening Riot in an incognito/private window and log in as the bot. From the Help & Support tab in settings there is an access token field - copy and paste that into your config. Most importantly: do not log out and instead just close the window. Logging out will make the token you just copied useless.

Note: Mjolnir expects to be free of rate limiting - see Synapse #6286 for information on how to achieve this.

Note: To deactivate users, move aliases, shutdown rooms, etc Mjolnir will need to be a server admin.

Docker installation (preferred)

Mjolnir is on Docker Hub as matrixdotorg/mjolnir but can be built yourself with docker build -t mjolnir ..

git clone https://github.com/matrix-org/mjolnir.git
cd mjolnir

# Copy and edit the config. It is not recommended to change the data path.
mkdir -p /etc/mjolnir/config
cp config/default.yaml /etc/mjolnir/config/production.yaml
nano /etc/mjolnir/config/production.yaml

docker run --rm -it -v /etc/mjolnir:/data matrixdotorg/mjolnir:latest

Build it (alternative installation)

This bot requires yarn and Node 14.

git clone https://github.com/matrix-org/mjolnir.git
cd mjolnir

yarn install
yarn build

# Copy and edit the config. It *is* recommended to change the data path.
cp config/default.yaml config/development.yaml
nano config/development.yaml

node lib/index.js

Quickstart guide

After your bot is up and running, you'll want to run a couple commands to get everything set up:

1. !mjolnir list create COC code-of-conduct-ban-list - This will create a new ban list with the shortcode COC and an alias of #code-of-conduct-ban-list:example.org. You will be invited to the room it creates automatically where you can change settings such as the visibility of the room.
2. !mjolnir default COC - This sets the default ban list to the list we just created to help with the ban commands later on.
3. Review the Moderator's Guide.
4. Review !mjolnir help to see what else the bot can do.

Synapse Module

This requires Synapse 1.53.0 or higher

Using the bot to manage your rooms is great, however if you want to use your ban lists (or someone else's) on your server to affect all of your users then a Synapse module is needed. Primarily meant to block invites from undesired homeservers/users, Mjolnir's Synapse module is a way to interpret ban lists and apply them to your entire homeserver.

First, install the module to your Synapse python environment:

pip install -e "git+https://github.com/matrix-org/mjolnir.git#egg=mjolnir&subdirectory=synapse_antispam"

Note: Where your python environment is depends on your installation method. Visit #synapse:matrix.org if you're not sure.

Then add the following to your homeserver.yaml:

modules:
  - module: mjolnir.Module
    config:
      # Prevent servers/users in the ban lists from inviting users on this
      # server to rooms. Default true.
      block_invites: true
      # Flag messages sent by servers/users in the ban lists as spam. Currently
      # this means that spammy messages will appear as empty to users. Default
      # false.
      block_messages: false
      # Remove users from the user directory search by filtering matrix IDs and
      # display names by the entries in the user ban list. Default false.
      block_usernames: false
      # The room IDs of the ban lists to honour. Unlike other parts of Mjolnir,
      # this list cannot be room aliases or permalinks. This server is expected
      # to already be joined to the room - Mjolnir will not automatically join
      # these rooms.
      ban_lists:
         - "!roomid:example.org"
      message_max_length:
         # Limit the characters in a message (event body) that a client can send in an event on this server.
         # By default there is no limit (beyond the the limit the spec enforces on event size).
         # Uncomment if you want messages to be limited to 510 characters.
         #threshold: 510

         # Limit messages only in certain rooms rooms.
         # By default all rooms will enforce the limit.
         # Uncomment if you want messages to only be subject to character limits in certain rooms.
         #rooms:
         #  - "!vMvyOCeCxHsggkmALd:localhost:9999"

         # Also hide messages from remote servers that are over the `message_limit`.
         # By default only events from this server will be limited.
         # WARNING: Remote users on other servers will still be able to messages over the limit.
         # Uncomment to enforce the `message_limit` on events from remote servers.
         #remote_servers: true

Note: Although this is described as a "spam checker", it does much more than fight spam.

Be sure to change the configuration to match your setup. Your server is expected to already be participating in the ban lists - if it is not, you will need to have a user on your homeserver join. The antispam module will not join the rooms for you.

If you change the configuration, you will need to restart Synapse. You'll also need to restart Synapse to install the plugin.

Enabling readable abuse reports

Since version 1.2, Mjölnir offers the ability to replace the Matrix endpoint used to report abuse and display it into a room, instead of requiring you to request this data from an admin API.

This requires two configuration steps:

1. In your Mjölnir configuration file, typically /etc/mjolnir/config/production.yaml, copy and paste the web section from default.yaml, if you don't have it yet (it appears with version 1.20) and set enabled: true for both web and abuseReporting.
2. Setup a reverse proxy that will redirect requests from ^/_matrix/client/r0/rooms/([^/]*)/report/(.*)$ to http://host:port/api/1/report/$1/$2, where host is the host where you run Mjölnir, and port is the port you configured in production.yaml. For an example nginx configuration, see test/nginx.conf. It's the confirmation we use during runtime testing.

Security note

This mechanism can extract some information from unencrypted rooms. We have taken precautions to ensure that this cannot be abused: the only case in which this feature will publish information from room foo is:

1. If it is used by a member of room foo; AND
2. If said member did witness the event; AND
3. If the event was unencrypted; AND
4. If the event was not redacted/removed/...

Essentially, this is a more restricted variant of the Admin APIs available on homeservers.

However, if you are uncomfortable with this, please do not activate this feature. Also, you should probably setup your production.yaml to ensure that the web server can only receive requests from your reverse proxy (e.g. localhost).

Development

TODO. It's a TypeScript project with a linter.

Development and testing with mx-tester

WARNING: mx-tester is currently work in progress, but it can still save you some time and is better than struggling with nothing.

If you have docker installed you can quickly get setup with a development environment by using mx-tester.

To use mx-tester you will need to have rust installed. You can do that at rustup or here, you should probably also check your distro's documentation first to see if they have specific instructions for installing rust.

Once rust is installed you can install mx-tester like so.

$ cargo install mx-tester

Once you have mx-tester installed you we will want to build a synapse image with synapse_antispam from the mjolnir project root.

$ mx-tester build

Then we can start a container that uses that image and the config in mx-tester.yml.

$ mx-tester up

Once you have called mx-tester up you can run the integration tests.

$ yarn test:integration

After calling mx-tester up, if we want to play with mojlnir locally we can run the following and then point a matrix client to http://localhost:9999. You should then be able to join the management room at #moderators:localhost:9999.

yarn test:manual

Once we are finished developing we can stop the synapse container.

mx-tester down

Running integration tests

The integration tests can be run with yarn test:integration. The config that the tests use is in config/harness.yaml and by default this is configured to work with the server specified in mx-tester.yml, but you can configure it however you like to run against your own setup.