CSRF filter

Cross-Site Request Forgery (CSRF) is an attack that occurs when a malicious third-party website exploits a vulnerability that allows them to submit an undesired request on a user’s behalf. To mitigate this attack this filter checks where a request is coming from to determine if the request’s origin is the same as it’s destination.

To help demonstrate how front-envoy can enforce CSRF policies, we are releasing a docker compose sandbox that deploys a service with both a frontend and backed. This service will be started on two different virtual machines with different origins.

The frontend has a field to input the remote domain of where you would like to send POST requests along with radio buttons to select the remote domain’s CSRF enforcement. The CSRF enforcement choices are:

Disabled: CSRF is disabled on the requested route. This will result in a successful request since there is no CSRF enforcement.

Shadow Mode: CSRF is not enforced on the requested route but will record if the request contains a valid source origin.

Enabled: CSRF is enabled and will return a 403 (Forbidden) status code when a request is made from a different origin.

Ignored: CSRF is enabled but the request type is a GET. This should bypass the CSRF filter and return successfully.

Step 1: Start all of our containers

Change to the examples/csrf/samesite directory, and start the containers:

$ pwd
envoy/examples/csrf/samesite
$ docker-compose pull
$ docker-compose up --build -d
$ docker-compose ps

          Name                        Command              State                            Ports
----------------------------------------------------------------------------------------------------------------------------
samesite_front-envoy_1      /docker-entrypoint.sh /bin ... Up      10000/tcp, 0.0.0.0:8000->8000/tcp, 0.0.0.0:8001->8001/tcp
samesite_service_1          /bin/sh -c /usr/local/bin/ ... Up      10000/tcp, 8000/tcp

Now, switch to the crosssite directory in the csrf example, and start the containers:

$ pwd
envoy/examples/csrf/crosssite
$ docker-compose up --build -d
$ docker-compose ps

          Name                       Command                State              Ports
-----------------------------------------------------------------------------------------------------
crosssite_front-envoy_1      /bin/sh -c /usr/local/bin/ ... Up      10000/tcp, 0.0.0.0:8002->8000/tcp
crosssite_service_1          /docker-entrypoint.sh /bin ... Up      10000/tcp

Step 2: Test Envoy’s CSRF capabilities

You can now open a browser at http://localhost:8002 to view your crosssite frontend service.

Enter the IP of the samesite machine to demonstrate cross-site requests. Requests with the enabled enforcement will fail. By default this field will be populated with localhost.

To demonstrate same-site requests open the frontend service for samesite at http://localhost:8000 and enter the IP address of the samesite machine as the destination.

Results of the cross-site request will be shown on the page under Request Results. Your browser’s CSRF enforcement logs can be found in the browser console and in the network tab.

For example:

Failed to load resource: the server responded with a status of 403 (Forbidden)

If you change the destination to be the same as one displaying the website and set the CSRF enforcement to enabled the request will go through successfully.

Step 3: Check stats of backend via admin

When Envoy runs, it can listen to admin requests if a port is configured. In the example configs, the backend admin is bound to port 8001.

If you browse to http://localhost:8001/stats you will be able to view all of the Envoy stats for the backend. You should see the CORS stats for invalid and valid origins increment as you make requests from the frontend cluster.

http.ingress_http.csrf.missing_source_origin: 0
http.ingress_http.csrf.request_invalid: 1
http.ingress_http.csrf.request_valid: 0