A Caddy module that blocks malicious traffic based on decisions made by CrowdSec.
This repository is currently a WIP. Things may change a bit.
CrowdSec is a free and open source security automation tool that uses local logs and a set of scenarios to infer malicious intent. In addition to operating locally, an optional community integration is also available, through which crowd-sourced IP reputation lists are distributed.
The architecture of CrowdSec is very modular. At its core is the CrowdSec Agent, which keeps track of all data and related systems. Bouncers are pieces of software that perform specific actions based on the decisions of the Agent.
This repository contains a custom CrowdSec Bouncer that can be embedded as a Caddy module. It consists of the follwing three main pieces:
The App is responsible for communicating with a CrowdSec Agent via the CrowdSec Local API and keeping track of the decisions of the Agent. The HTTP Handler checks client IPs of incoming requests against the decisions stored by the App. This way, multiple independent HTTP Handlers or Connection Matchers can use the storage exposed by the App. The App can be configured to use either the StreamBouncer, which gets decisions via a HTTP polling mechanism, or the LiveBouncer, which sends a request on every incoming HTTP request or Layer 4 connection setup.
Get the module
# get the http handler
go get github.com/hslatman/caddy-crowdsec-bouncer/http
# get the layer4 connection matcher (only required if you need support for TCP/UDP level blocking)
go get github.com/hslatman/caddy-crowdsec-bouncer/layer4Create a (custom) Caddy server (or use xcaddy)
package main
import (
cmd "github.com/caddyserver/caddy/v2/cmd"
_ "github.com/caddyserver/caddy/v2/modules/standard"
// import the http handler
_ "github.com/hslatman/caddy-crowdsec-bouncer/http"
// import the layer4 matcher (in case you want to block connections to layer4 servers using CrowdSec)
_ "github.com/hslatman/caddy-crowdsec-bouncer/layer4"
)
func main() {
cmd.Main()
}Example Caddyfile:
{
debug
crowdsec {
api_url http://localhost:8080
api_key <api_key>
ticker_interval 15s
#disable_streaming
#enable_hard_fails
}
}
localhost {
route {
crowdsec
respond "Allowed by CrowdSec!"
}
}Configuration using a Caddyfile is only supported for HTTP handlers. You'll also need to use a recent version of Caddy (i.e. 2.7.3 and newer) and Go 1.20 (or newer). In case you want to use the CrowdSec bouncer on TCP or UDP level, you'll need to configure Caddy using the native JSON format. An example configuration is shown below:
{
"apps": {
"crowdsec": {
"api_key": "<insert_crowdsec_local_api_key_here>",
"api_url": "http://127.0.0.1:8080/",
"ticker_interval": "10s",
"enable_streaming": true,
"enable_hard_fails": false,
},
"http": {
"http_port": 9080,
"https_port": 9443,
"servers": {
"example": {
"listen": [
"127.0.0.1:9443"
],
"routes": [
{
"group": "example-group",
"match": [
{
"path": [
"/*"
]
}
],
"handle": [
{
"handler": "crowdsec"
},
{
"handler": "static_response",
"status_code": "200",
"body": "Hello World!"
},
{
"handler": "headers",
"response": {
"set": {
"Server": ["caddy-cs-bouncer-example-server"]
}
}
}
]
}
],
"logs": {}
}
}
},
"layer4": {
"servers": {
"https_proxy": {
"listen": ["localhost:8443"],
"routes": [
{
"match": [
{
"crowdsec": {},
"tls": {}
}
],
"handle": [
{
"handler": "proxy",
"upstreams": [
{
"dial": ["localhost:9443"]
}
]
}
]
}
]
}
}
},
}
}Run the Caddy server
# with a Caddyfile
go run main.go run -config Caddyfile
# with JSON configuration
go run main.go run -config config.jsonThis repository also contains an example using Docker. Steps to run this demo are as follows:
# run CrowdSec container
$ docker compose up -d crowdsec
# add the Caddy bouncer, generating an API key
$ docker compose exec crowdsec cscli bouncers add caddy-bouncer
# copy and paste the API key in the ./docker/config.json file
# below is the git diff after changing the appropriate line:
$ git diff
- "api_key": "<api_key>",
+ "api_key": "9e4ac94cf9aebaa3625a1d51951230a9",
# run Caddy; at first run a custom build will be created using xcaddy
$ docker compose up -d caddy
# tail the logs
$ docker compose logs -tfYou can then access https://localhost:9443 and https://localhost:8443. The latter is an example of using the Layer 4 App and will simply proxy to port 9443 in this case.
If your Caddy server with this bouncer is deployed behind a proxy, a CDN or another system fronting the web server, the IP of the client requesting a resource is masked by the system that sits between the client and your server.
Starting with v0.3.1, the HTTP handler relies on Caddy to determine the actual client IP of the system performing the HTTP request.
The new logic was implemented as part of caddy#5104, and released with Caddy v2.7.0.
The IP that Caddy determines is used to check against the CrowdSec decisions to see if it's allowed in or not.
Caddy determines the actual client IP from the X-Forwarded-For header by default, but it is possible to change this using the client_ip_headers directive in the global settings.
The setting depends on the trusted_proxies directive to be set, so that the IP reported in the X-Forwarded-For (or one of the headers you configure as override) can be trusted.
For older versions of this Caddy module, and for older versions of Caddy (up to v2.4.6), the realip module can be used instead.