smallwebwaf/README.md

# smallwebwaf

`smallwebwaf` is a simple, fast, logging web application firewall for people who
host their own services. It is one small container that sits between your
reverse proxy (traefik) and one application: traefik points at `smallwebwaf`,
and `smallwebwaf` points at the app. It needs one setting, the address of the
app, and protects the app from the first request with defaults chosen for a
service on the open internet. It keeps its state in memory and in JSON files you
can read and edit, and writes a detailed JSON log line for every request.

Status: design stage. This repository currently holds the documents only; no
code has been written. The design is in [`SPEC.md`](SPEC.md), and the survey of
existing tools that led to it is in [`EVALUATION.md`](EVALUATION.md).

## Why

Small self-hosted sites now receive a great deal of traffic nobody asked for:
scrapers that ignore `robots.txt` and crawl every commit of every repository on
a public git server, vulnerability scanners walking through lists of WordPress
and `.env` paths, and credential-guessing bots. Most of it comes from a small
number of hosting networks and countries. A single-person operation has no abuse
desk and no CDN contract; it needs something small that can be put in front of
one service and left alone.

The existing tools each solve part of this. Rule-based firewalls catch attack
payloads but do not limit request rates. Rate limiters count requests but cannot
tell a residential visitor from a rented server farm. The products that do most
of it want several containers, a database and a web console. None of them can
say "clients from these networks are banned after half as many requests as
anyone else", which is the most useful thing to be able to say when nearly all
abuse comes from a known list of AS numbers. [`EVALUATION.md`](EVALUATION.md)
goes through the candidates one by one.

`smallwebwaf` is meant to fill that gap:

- protect a service from misbehaving scrapers and scanners with per-client
  request and byte limits over a minute, an hour and a day;
- lower those limits for the countries and AS numbers that abuse commonly comes
  from, so their clients are banned after fewer requests than others;
- ban abusers: briefly at first, longer each time they come back, and
  permanently when they keep at it; a scanner's first probe bans it for seven
  days;
- log everything in a form that is easy to search and ship elsewhere;
- stay small enough to understand: one binary, one container, environment
  variables, no database, one required setting.

## Proposed features

- Reverse proxy for one upstream application, streaming in both directions, with
  WebSocket support. One `smallwebwaf` per app.
- Internet-ready out of the box: only `UPSTREAM_URL` must be set, and every
  other setting has a default chosen for a service facing the internet in 2026.
- Real client address worked out from `X-Forwarded-For`, trusting only the proxy
  networks you list, by default the private address ranges. IPv6 clients are
  counted by /64.
- Size and time limits on requests and responses, both between the client and
  `smallwebwaf` and between `smallwebwaf` and the app: by default a request may
  take 60 seconds and 100 MB, a response 30 minutes and 5 GB.
- Rate limits per client on requests per minute, per hour and per day, and on
  bytes per minute, per hour and per day, on by default and set well above what
  real visitors need.
- Netblocks that bypass rate limiting, netblocks that bypass everything, and
  netblocks that are always refused.
- AS number and country lookup for every client from the IPinfo Lite database
  file, which you download and mount (see "Lookup database" below).
- Biased limits: listed AS numbers and countries get a percentage of every
  limit, for example 50 percent for common abuse-source networks, so their
  clients are banned after fewer requests. Zero percent is a zero allowance: the
  first request breaks the limit and bans the client.
- Attack detection:
    - a directory of plain text rule files, one regex per line, for catching
      scanning and penetration probes; easy to edit by hand, and picked up while
      running;
    - the OWASP Core Rule Set, run by the Coraza engine, refusing the requests
      it flags;
    - trap paths and bursts of error responses.
- Bans:
    - a clear sign of attack, such as a probe for a `.env` file or a scanner's
      user agent, bans for seven days on the first request, and any further
      request during those days makes the ban permanent;
    - breaking a limit bans for an hour; breaking one again within a day of a
      ban ending triples the length, and a ban that would last longer than seven
      days is permanent instead;
    - every ban carries notes on why it was made, to help decide whether to lift
      it.
- IP reputation: downloadable blocklists, DNS blocklists, AbuseIPDB, and an
  optional feed of decisions from a CrowdSec engine. Lookups happen in the
  background and never delay a request. None is on until you add it.
- Alerts on attacks and bans to a generic webhook, Slack or ntfy, with a
  cooldown and an hourly cap so a wide attack cannot flood the channel.
- Anomaly alerts when requests or bytes per minute or hour cross a threshold you
  set, for a single client, its surrounding netblock, an AS number, a named
  netblock or the whole service.
- Observe mode: log and alert on every decision while refusing nothing.
- Request log: one JSON object per request on stdout with the usual web log
  fields, the decision taken and why, AS number and country, and timings.
  Optionally also sent to a remote syslog server.
- Prometheus metrics on their own port.
- State (bans with their notes, each client's counters and history, the
  reputation cache) held in memory and kept in readable JSON files that always
  hold a copy of it, so a restart loses nothing. Edit a file, or add a rule
  file, and the running `smallwebwaf` picks up the change. Nothing is read from
  disk while serving a request.
- A small admin endpoint for health checks, listing, adding and lifting bans,
  and asking why a given address was refused.

Not planned: TLS termination, routing for several apps, browser challenges
(captcha or proof of work), a web console, or defence against floods large
enough to fill the host's network link.

## How it works, in short

For each request `smallwebwaf`:

- works out who the client really is;
- lets it straight through if it is on the bypass list, refuses it if it is on
  the deny list or currently banned;
- looks up its AS number and country, and any cached reputation verdict;
- picks the client's limit percentage from those;
- checks the minute, hour and day request counters against the limits, and bans
  the client if it breaks one;
- checks the request against the rule files and the Core Rule Set, and bans the
  client at once for a clear sign of attack;
- forwards it to the app and streams the response back, within the size and time
  limits;
- counts the bytes and any error response, bans the client if it broke a limit,
  updates its history, sends any alerts that are due, and writes the log line.

A minimal deployment beside an app in docker-compose. `UPSTREAM_URL` is the only
setting:

```yaml
services:
    app:
        image: example/app
        networks: [internal]

    waf:
        image: <registry>/smallwebwaf:<pinned digest>
        environment:
            UPSTREAM_URL: http://app:3000
        volumes: [waf-state:/data]
        networks: [internal, traefik]
        labels:
            traefik.enable: "true"
            traefik.http.routers.app.rule: Host(`app.example.invalid`)
            traefik.http.services.app.loadbalancer.server.port: "8080"

volumes:
    waf-state:

networks:
    internal:
    traefik:
        external: true
```

The volume keeps bans and client history in a place you choose; without it
`smallwebwaf` still starts, on a volume docker creates for it.

A rule file is one rule per line: a name, what to match against, what to do, and
a regex.

```
env-file       path        ban  (?i)/\.env(\.[a-z]+)?$
scanner-agent  user_agent  ban  (?i)\b(sqlmap|nikto|nuclei|wpscan)\b
```

[`SPEC.md`](SPEC.md) has the full design: every environment variable, the ban
rules, the rule file format, the state files, the log fields, the metrics,
failure behaviour and the build order.

## Lookup database

AS number and country lookups, and the biased limits that use them, need the
free IPinfo Lite database (`ipinfo_lite.mmdb`). You download it with your own
IPinfo account, mount it into the container, point `LOOKUP_DB_PATH` at it and
refresh it when you choose; `smallwebwaf` never downloads it itself. IPinfo
releases it under the Creative Commons Attribution-ShareAlike 4.0 International
License and asks for attribution, in its own words on https://ipinfo.io/lite:
"The attribution requirements can be met by giving our service credit as your
data source. Simply place a link to IPinfo on the website, application, or
social media account that uses our data." Its example of such a credit is a link
mentioning "IP address data is powered by IPinfo". A service that uses the
database through `smallwebwaf` should carry that link.

## Documents

- [`SPEC.md`](SPEC.md): the design.
- [`EVALUATION.md`](EVALUATION.md): what already exists, what each tool covers
  and misses, and why none was adopted.