reaction/README.md

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# reaction
a program that scans program outputs, such as logs,
for repeated patterns, such as failed login attempts,
and takes action, such as banning ips.
(adapted from [fail2ban](http://fail2ban.org)'s presentation 😄)
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🚧 this program hasn't received external audit. however, it already works well on my servers 🚧
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## rationale
i was using fail2ban since quite a long time, but i was a bit frustrated by it's cpu consumption
and all its heavy default configuration.
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in my view, a security-oriented program should be simple to configure (`sudo` is a very bad example!)
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and an always-running daemon should be implemented in a fast language.
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<a href="https://u.ppom.me/reaction.webm">📽️ french example</a>
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## configuration
this configuration file is all that should be needed to prevent bruteforce attacks on an ssh server.
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see [reaction.service](./config/reaction.service) and [reaction.yml](./app/reaction.yml) for the fully explained examples.
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`/etc/reaction.yml`
```yaml
definitions:
- &iptablesban [ "iptables" "-w" "-I" "reaction" "1" "-s" "<ip>" "-j" "block" ]
- &iptablesunban [ "iptables" "-w" "-D" "reaction" "1" "-s" "<ip>" "-j" "block" ]
patterns:
ip: '(([0-9]{1,3}\.){3}[0-9]{1,3})|([0-9a-fA-F:]{2,90})'
streams:
ssh:
cmd: [ "journalctl" "-fu" "sshd.service" ]
filters:
failedlogin:
regex:
- authentication failure;.*rhost=<ip>
retry: 3
retry-period: 6h
actions:
ban:
cmd: *iptablesban
unban:
cmd: *iptablesunban
after: 48h
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```
`/etc/systemd/system/reaction.service`
```systemd
[Unit]
WantedBy=multi-user.target
[Service]
ExecStart=/path/to/reaction -c /etc/reaction.yml
ExecStartPre=/path/to/iptables -w -N reaction
ExecStartPre=/path/to/iptables -w -A reaction -j ACCEPT
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ExecStartPre=/path/to/iptables -w -I reaction 1 -s 127.0.0.1 -j ACCEPT
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ExecStartPre=/path/to/iptables -w -I INPUT -p all -j reaction
ExecStopPost=/path/to/iptables -w -D INPUT -p all -j reaction
ExecStopPost=/path/to/iptables -w -F reaction
ExecStopPost=/path/to/iptables -w -X reaction
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StateDirectory=reaction
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RuntimeDirectory=reaction
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WorkingDirectory=/var/lib/reaction
```
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### database
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the working directory of `reaction` will be used to create and read from the embedded database.
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if you don't know where to start it, `/var/lib/reaction` should be a sane choice.
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### socket
the socket allowing communication between the cli and server will be created at `/run/reaction/reaction.socket`.
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### compilation
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you'll need the go toolchain.
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```shell
$ go build .
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```
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### nixos
in addition to the [package](https://framagit.org/ppom/nixos/-/blob/cf5448b21ae3386265485308a6cd077e8068ad77/pkgs/reaction/default.nix)
and [module](https://framagit.org/ppom/nixos/-/blob/cf5448b21ae3386265485308a6cd077e8068ad77/modules/common/reaction.nix)
that i didn't tried to upstream to nixpkgs yet (although they are ready), i use extensively reaction on my servers. if you're using nixos,
consider reading and building upon [my own building blocks](https://framagit.org/ppom/nixos/-/blob/cf5448b21ae3386265485308a6cd077e8068ad77/modules/common/reaction-variables.nix),
[my own non-root reaction conf, including conf for SSH, port scanning & Nginx common attack URLS](https://framagit.org/ppom/nixos/-/blob/cf5448b21ae3386265485308a6cd077e8068ad77/modules/common/reaction-custom.nix),
and the configuration for [nextcloud](https://framagit.org/ppom/nixos/-/blob/cf5448b21ae3386265485308a6cd077e8068ad77/modules/musi/file.ppom.me.nix#L53),
[vaultwarden](https://framagit.org/ppom/nixos/-/blob/cf5448b21ae3386265485308a6cd077e8068ad77/modules/musi/vaultwarden.nix#L45),
and [maddy](https://framagit.org/ppom/nixos/-/blob/cf5448b21ae3386265485308a6cd077e8068ad77/modules/musi/mail.nix#L74). see also an [example](https://framagit.org/ppom/nixos/-/blob/cf5448b21ae3386265485308a6cd077e8068ad77/modules/musi/mail.nix#L85) where it does something else than banning IPs.