# Agent – f2b-webctl

Every fail2ban host runs the agent [`f2b-webctl`](../agent/f2b-webctl): a small Python
script (standard library only) started as SSH **forced command** of the web UI's key.
The web UI cannot run anything else on the host.

| Command (sent by the web UI) | Effect |
|---|---|
| `list` | all jails with their banned IPs (JSON) |
| `ban <ip>` | ban permanently in the manual jail (`manual-block`) |
| `unban <jail> <ip>` | unban in one jail |
| `unban-all <ip>` | unban in all jails |
| `version` | agent version |

Never banned, whatever the web UI sends:

- private, loopback, link-local, CGNAT, multicast and reserved ranges
  (`10/8`, `172.16/12`, `192.168/16`, `100.64/10`, `127/8`, `169.254/16`, `fc00::/7`, `fe80::/10`, …)
- all addresses of the host itself and the address the web UI connects from
- everything listed in `PROTECTED` in `/etc/f2b-webctl.conf` (e.g. your home IP)

Every action is logged to syslog (facility `auth`, tag `f2b-webctl`), including rejected ones.

## Requirements

| | |
|---|---|
| fail2ban | ≥ 0.11, running (`fail2ban-client ping`) – older versions without `--with-time` work, but without start/end times |
| python3 | ≥ 3.8 |
| sshd | reachable from the web UI host |
| sudo | for the default user `f2bweb` (`apt install sudo`); not needed with `--user root` |
| bash, ssh-keygen | for the installer |

Works on Debian, Ubuntu, Proxmox VE and other systemd or non-systemd Linux systems –
bare metal, VMs, LXC containers (privileged or unprivileged) and Docker hosts.

## Installation

You need the public key printed by `fail2ban-webui keygen` and the address the web UI
connects from (the public IP of the Docker host, or its LAN address).

```bash
# as root on the fail2ban host
git clone https://git.retronerd.at/schiwagoa/fail2ban-webui.git /tmp/fail2ban-webui
cd /tmp/fail2ban-webui/agent

echo 'ssh-ed25519 AAAA… fail2ban-webui' > /tmp/webui.pub

# see what would happen
bash install.sh --key-file /tmp/webui.pub --from 198.51.100.10 --dry-run
# install
bash install.sh --key-file /tmp/webui.pub --from 198.51.100.10
```

Without `git`: download the three files `f2b-webctl`, `install.sh` and `uninstall.sh` from
the `agent/` directory into one directory and run `install.sh` from there.

The installer shows a summary and asks before it changes anything:

```
fail2ban-webui agent 1.0.0  –  fail2ban 1.1.0  –  web01

  script         /usr/local/sbin/f2b-webctl
  config         /etc/f2b-webctl.conf
  SSH user       f2bweb (will be created)
  sudo rule      /etc/sudoers.d/f2b-webctl
  key file       /var/lib/f2bweb/.ssh/authorized_keys
  key            256 SHA256:zfwh… (ED25519)
  allowed from   198.51.100.10
  manual jail    manual-block (will be created)
  backups        /var/backups/fail2ban-webui-agent
```

What it does:

1. backs up every file it is going to change to `--backup-dir`
2. installs `/usr/local/sbin/f2b-webctl` (`root:root 0750`)
3. writes `/etc/f2b-webctl.conf` (kept if it already exists)
4. creates the system user `f2bweb` (home `/var/lib/f2bweb`, no password) and the sudo rule
   ```
   Defaults!/usr/local/sbin/f2b-webctl env_keep += "SSH_ORIGINAL_COMMAND SSH_CLIENT"
   f2bweb ALL=(root) NOPASSWD: /usr/local/sbin/f2b-webctl
   ```
5. adds the key with all restrictions:
   ```
   restrict,from="198.51.100.10",command="sudo -n /usr/local/sbin/f2b-webctl" ssh-ed25519 AAAA… fail2ban-webui
   ```
6. creates the jail `manual-block` if it does not exist (see below)
7. runs a self test through the same sudo path the web UI uses

Running the installer again is safe: it updates the script, replaces the key entry and
keeps your configuration.

### Options

| Option | Default | Meaning |
|---|---|---|
| `--key-file FILE` / `--key "KEY"` | – | public key of the web UI (required) |
| `--from ADDRESSES` | any | only accept the key from these IPs/networks (comma separated). **Strongly recommended.** |
| `--user NAME` | `f2bweb` | SSH user; `root` works without sudo |
| `--authorized-keys-file PATH` | `~USER/.ssh/authorized_keys` | where the key entry goes – see [managed keys](#hosts-with-managed-authorized_keys) |
| `--manual-jail NAME` | `manual-block` | jail for manual bans |
| `--banaction ACTION` | from `jail.local` | banaction of a newly created manual jail |
| `--protect NETWORKS` | – | additional protected addresses (only when the config file is written) |
| `--no-jail` | – | do not create the manual jail |
| `--force-config` | – | overwrite an existing `/etc/f2b-webctl.conf` |
| `--backup-dir DIR` | `/var/backups/fail2ban-webui-agent` | backups of changed files |
| `--dry-run` | – | only show what would be done |
| `-y`, `--yes` | – | do not ask |

The installer warns when sshd would not read the chosen key file (`AuthorizedKeysFile`),
when `AllowUsers`/`AllowGroups` are set, or when `--user root` meets `PermitRootLogin no`.

## The manual jail

Bans from the web UI go into one jail, `manual-block` by default, with `bantime = -1`
(permanent). If the jail does not exist, the installer creates:

`/etc/fail2ban/filter.d/manual-block.conf`

```ini
# fail2ban-webui: never matches – the jail is only filled via
# "fail2ban-client set manual-block banip <ip>"
[Definition]
failregex = ^FAIL2BAN-WEBUI-NEVER-MATCHES <HOST>$
ignoreregex =
```

`/etc/fail2ban/jail.d/manual-block.local`

```ini
# fail2ban-webui: permanent manual bans from the web UI
[manual-block]
enabled  = true
filter   = manual-block
backend  = polling
logpath  = /var/log/fail2ban-manual-block.log
maxretry = 1
bantime  = -1
```

The jail uses your default `banaction` from `jail.local`. Bans survive restarts through
the fail2ban database.

An existing jail with that name is never touched – if you already have a jail for manual
bans, pass its name with `--manual-jail`.

### Docker hosts

fail2ban's default actions block in the `INPUT` chain. Traffic to **published Docker
ports** does not pass `INPUT` but `FORWARD` → `DOCKER-USER`, so those bans would not
affect your containers. For a Docker host, create the manual jail with an action that
uses the `DOCKER-USER` chain, e.g. with iptables:

```bash
bash install.sh --key-file /tmp/webui.pub --from 198.51.100.10 \
  --banaction "iptables-allports[chain=DOCKER-USER]"
```

Check the result after the first ban:

```bash
iptables -S DOCKER-USER | head
```

If the web UI runs on the same Docker host, use `address: host.docker.internal` in
`hosts.yaml` and allow SSH from the Docker network if a firewall (e.g. UFW) blocks it:

```bash
ufw allow from 172.23.51.0/24 to any port 22 proto tcp comment 'fail2ban-webui'
```

and install the agent with `--from 172.23.51.10`.

### LXC containers

The agent runs inside the container where fail2ban runs – nothing special is needed.
In **unprivileged** containers fail2ban itself must be able to change the container's
firewall (nftables/iptables inside the CT); test with a manual ban:

```bash
fail2ban-client set manual-block banip 203.0.113.1 && nft list ruleset | grep 203.0.113.1
fail2ban-client set manual-block unbanip 203.0.113.1
```

### Hosts with managed authorized_keys

Some tools (Ansible, Keywarden, cloud-init, …) overwrite `~/.ssh/authorized_keys`.
Put the key into a file they do not manage and make sure sshd reads it:

```bash
grep -i '^AuthorizedKeysFile' /etc/ssh/sshd_config /etc/ssh/sshd_config.d/*.conf
# e.g. AuthorizedKeysFile .ssh/authorized_keys .ssh/authorized_keys2

bash install.sh --key-file /tmp/webui.pub --from 198.51.100.10 \
  --user root --authorized-keys-file /root/.ssh/authorized_keys2
```

## Configuration – /etc/f2b-webctl.conf

```ini
# fail2ban-webui agent (f2b-webctl) – settings
# Jail used for manual bans from the web UI
MANUAL_JAIL=manual-block
# Addresses/networks that must never be banned (comma separated), e.g. your home IP.
# Private, loopback, link-local and CGNAT ranges are always protected.
PROTECTED=203.0.113.25,2001:db8:1234::/48
# Also protect all addresses of this host and the address of the web UI (yes/no)
PROTECT_OWN_ADDRESSES=yes
PROTECT_CLIENT=yes
```

Changes take effect immediately – the agent reads the file on every call.

## Testing on the host

```bash
# as root, directly
f2b-webctl list | python3 -m json.tool | head -30
f2b-webctl ban 10.0.0.1          # → rejected, protected

# the same path as the web UI (user f2bweb through sudo)
runuser -u f2bweb -- env SSH_ORIGINAL_COMMAND=version sudo -n /usr/local/sbin/f2b-webctl

# what the agent did
journalctl -t f2b-webctl --since today      # or: grep f2b-webctl /var/log/auth.log
```

## Update

Run the installer of the new version again with the same options. Your configuration
and the jail are kept; the script and the key entry are replaced.

## Uninstall

```bash
bash uninstall.sh --dry-run
bash uninstall.sh
```

| Option | Meaning |
|---|---|
| `--user NAME` | agent user (default `f2bweb`) |
| `--authorized-keys-file PATH` | file with the key entry |
| `--remove-user` | also delete the user and its home |
| `--remove-jail` | also delete the manual jail – **lifts all manual bans** (they are listed first) |
| `--backup-dir DIR`, `--dry-run`, `--yes` | as for the installer |

## Manual installation

If you prefer to do it by hand, these are all the steps the installer performs:

```bash
install -o root -g root -m 0750 f2b-webctl /usr/local/sbin/f2b-webctl
nano /etc/f2b-webctl.conf                          # content see above

useradd --system --create-home --home-dir /var/lib/f2bweb --shell /bin/sh f2bweb
usermod -p '*' f2bweb
visudo -f /etc/sudoers.d/f2b-webctl                # content see "What it does", step 4

install -d -o f2bweb -g f2bweb -m 700 /var/lib/f2bweb/.ssh
nano /var/lib/f2bweb/.ssh/authorized_keys          # line see step 5
chown f2bweb: /var/lib/f2bweb/.ssh/authorized_keys
chmod 600 /var/lib/f2bweb/.ssh/authorized_keys

# manual jail: the two files from "The manual jail", then
touch /var/log/fail2ban-manual-block.log
fail2ban-client reload
```