reaction

A daemon that scans program outputs for repeated patterns, and takes action.

A common usage is to scan ssh and webserver logs, and to ban hosts that cause multiple authentication errors.

🚧 This program hasn't received external audit. however, it already works well on my servers 🚧

Current project status

reaction just reached v2.0.0-rc2 version, which is a complete rust rewrite of reaction. It's in feature parity with the Go version, and breaking changes should be small.

See https://reaction.ppom.me/migrate-to-v2.html

Rationale

I was using the honorable fail2ban since quite a long time, but i was a bit frustrated by its cpu consumption and all its heavy default configuration.

In my view, a security-oriented program should be simple to configure and an always-running daemon should be implemented in a faster language.

reaction does not have all the features of the honorable fail2ban, but it's ~10x faster and has more manageable configuration.

📽️ quick french name explanation 😉

🇬🇧 in-depth blog article / 🇫🇷 french version

Configuration

YAML and JSONnet (more powerful) are supported. both are extensions of JSON, so JSON is transitively supported.

• See reaction.yml or reaction.jsonnet for a fully explained reference
• See server.jsonnet for a real-world configuration
• See reaction.example.service for a systemd service file
• This minimal example shows what's needed to prevent brute force attacks on an ssh server (please take a look at more complete references before starting 🆙):

/etc/reaction.yml

patterns:
  ip:
    regex: '(([0-9]{1,3}\.){3}[0-9]{1,3})|([0-9a-fA-F:]{2,90})'

start:
  - [ 'ip46tables', '-w', '-N', 'reaction' ]
  - [ 'ip46tables', '-w', '-A', 'reaction', '-j', 'ACCEPT' ]
  - [ 'ip46tables', '-w', '-I', 'reaction', '1', '-s', '127.0.0.1', '-j', 'ACCEPT' ]
  - [ 'ip46tables', '-w', '-I', 'INPUT', '-p', 'all', '-j', 'reaction' ]

stop:
  - [ 'ip46tables', '-w', '-D', 'INPUT', '-p', 'all', '-j', 'reaction' ]
  - [ 'ip46tables', '-w', '-F', 'reaction' ]
  - [ 'ip46tables', '-w', '-X', 'reaction' ]

streams:
  ssh:
    cmd: [ 'journalctl', '-fu', 'sshd.service' ]
    filters:
      failedlogin:
        regex:
          - 'authentication failure;.*rhost=<ip>'
        retry: 3
        retryperiod: '6h'
        actions:
          ban:
            cmd: [ 'ip46tables', '-w', '-I', 'reaction', '1', '-s', '<ip>', '-j', 'block' ]
          unban:
            cmd: [ 'ip46tables', '-w', '-D', 'reaction', '1', '-s', '<ip>', '-j', 'block' ]
            after: '48h'

/etc/reaction.jsonnet

local iptables(args) = [ 'ip46tables', '-w' ] + args;
local banFor(time) = {
  ban: {
    cmd: iptables(['-A', 'reaction', '-s', '<ip>', '-j', 'reaction-log-refuse']),
  },
  unban: {
    after: time,
    cmd: iptables(['-D', 'reaction', '-s', '<ip>', '-j', 'reaction-log-refuse']),
  },
};
{
  patterns: {
    ip: {
      regex: @'(?:(?:[ 0-9 ]{1,3}\.){3}[0-9]{1,3})|(?:[0-9a-fA-F:]{2,90})',
    },
  },
  start: [
    iptables([ '-N', 'reaction' ]),
    iptables([ '-A', 'reaction', '-j', 'ACCEPT' ]),
    iptables([ '-I', 'reaction', '1', '-s', '127.0.0.1', '-j', 'ACCEPT' ]),
    iptables([ '-I', 'INPUT', '-p', 'all', '-j', 'reaction' ]),
  ],
  stop: [
    iptables([ '-D', 'INPUT', '-p', 'all', '-j', 'reaction' ]),
    iptables([ '-F', 'reaction' ]),
    iptables([ '-X', 'reaction' ]),
  ],
  streams: {
    ssh: {
      cmd: [ 'journalctl', '-fu', 'sshd.service' ],
      filters: {
        failedlogin: {
          regex: [ @'authentication failure;.*rhost=<ip>' ],
          retry: 3,
          retryperiod: '6h',
          actions: banFor('48h'),
        },
      },
    },
  },
}

Database

The embedded database is stored in the working directory. If you don't know where to start reaction, /var/lib/reaction should be a sane choice.

CLI

• reaction start runs the server
• reaction show show pending actions (ie. bans)
• reaction flush permits to run pending actions (ie. clear bans)
• reaction test-regex permits to test regexes
• reaction help for full usage.

ip46tables

ip46tables is a minimal c program present in its own subdirectory with only standard posix dependencies.

It permits to configure iptables and ip6tables at the same time. It will execute iptables when detecting ipv4, ip6tables when detecting ipv6 and both if no ip address is present on the command line.

Wiki

You'll find more ressources, service configurations, etc. on the wiki!

We recommend that you read the Good Practices chapters before starting.

Installation

Binaries

Executables and .deb packages are provided in the releases page, for x86-64/amd64 linux and aarch64/arm64 linux.

Signature verification and installation instructions are provided in the releases page.

Provided binaries are compiled by running nix-shell release.py on a NixOS machine with docker installed.

NixOS

reaction is packaged, but the module has not yet been upstreamed.

OpenBSD

wiki

Compilation

You'll need a recent rust toolchain for reaction and a c compiler for ip46tables.

$ make

Don't hesitate to take a look at the Makefile to understand what's happening!

Installation

To install the binaries

make install

To install the systemd file as well

make install_systemd

Contributing

We, as participants in the open source ecosystem, are ethically responsible for the software and hardware we help create - as it can be used to perpetuate inequalities or help empower marginalized communities, and fight against patriarchy, capitalism, sexism, gender violence, racism, ableism, homophobia, colonialism, fascism, surveillance, and oppressive control.

• NGI's Diversity and Inclusion Guide

I'll do my best to maintain a safe contribution place, as free as possible from discrimination and elitism. Your ideas are welcome in the issues. Contributions are welcome.

For any substantial feature, please file an issue first, to be assured that we agree on the feature, and to avoid unnecessary work.

I recommend reading ARCHITECTURE.md first. This is a quick tour of the codebase, which should save time to new contributors.

You can also join this Matrix development room: #reaction-dev-en:club1.fr. French version: #reaction-dev-fr:club1.fr.

Help

You can ask for help in the issues or in this Matrix room: #reaction-users-en:club1.fr. French version: #reaction-users-fr:club1.fr.

Funding

This is a free time project, so I'm not working on schedule. However, if you're willing to fund the project, I can priorise and plan paid work. This includes features, documentation and specific JSONnet configurations.