Testing the Rule Set

Testing for rule developers

Well, you managed to write your rule, but now want to see if if can be added to the CRS? This document should help you to test it using the same tooling the project uses for its tests.

CRS uses go-ftw to run test cases. go-ftw is the successor to the previously used test runner ftw. The CRS project no longer uses ftw but it us still useful for running tests of older CRS versions.


Before you start to run tests, you should set up your environment. You can use Docker to run a web server with CRS integration or use your existing environment.

Setting up Docker containers

For testing, we use the container images from our project. We “bind mount” the rules in the CRS Git repository to the web server container and then instruct go-ftw to send requests to it.

To test we need two containers: the WAF itself, and a backend, provided in this case by the http://httpbin.org project. The docker-compose.yml in the CRS Git repository is a ready-to-run configuration for testing, to be used with the docker compose command.

-> The supported platform is ModSecurity 2 with Apache httpd

Let’s start the containers by executing the following command:

❯ docker compose -f tests/docker-compose.yml up -d modsec2-apache

Creating network "tests_default" with the default driver
Creating tests_backend_1 ... done
Creating modsec2-apache  ... done
❯ docker ps
CONTAINER ID   IMAGE                              COMMAND                  CREATED          STATUS         PORTS                               NAMES
785a6f6a3cb6   owasp/modsecurity-crs:3.3-apache   "/docker-entrypoint.…"   7 seconds ago    Up 3 seconds>80/tcp, :::80->80/tcp   modsec2-apache
bb8d5a7f256d   kennethreitz/httpbin               "gunicorn -b…"   10 seconds ago   Up 7 seconds   80/tcp                              tests_backend_1

Excellent, our containers are running, now we can start our tests.

Using your own environment for testing

If you have your own environment set up, you can configure that for testing. Please follow these instructions to install the WAF server locally.

-> The supported platform is ModSecurity 2 with Apache httpd. If you want to run the tests against nginx, you can do that too, but nginx uses libmodsecurity3, which is not fully compatible with Apache httpd + ModSecurity 2.

If you want to run the complete test suite of CRS 4.0 with go-ftw, you need to make some modifications to your setup. This is because the test cases for 4.0 contain some extra data for responses, letting us test the RESPONSE-* rules too. Without the following steps these tests will fail.

To enable response handling for tests you will need the following additional packages: python3-gunicorn, gunicorn and python3-httpbin.

Start httpbin

httpbin is a simple HTTP request & response service. You send a request, and it sends it back in the response.

You can start httpbin with this command:

/usr/bin/python3 /usr/bin/gunicorn --error-logfile - --access-logfile - --access-logformat "%(h)s %(t)s %(r)s %(s)s Content-Type: %({Content-Type}i)s" httpbin:app
[2023-12-14 15:59:53 +0100] [4012] [INFO] Starting gunicorn 20.1.0
[2023-12-14 15:59:53 +0100] [4012] [INFO] Listening at: (4012)
[2023-12-14 15:59:53 +0100] [4012] [INFO] Using worker: sync
[2023-12-14 15:59:53 +0100] [4013] [INFO] Booting worker with pid: 4013

As you can see the HTTP server listens on, you can check it:

$ curl -X POST -H "Content-Type: application/json" -d '{"foo":"bar"}' "http://localhost:8000/anything"
  "args": {},
  "data": "{\"foo\":\"bar\"}",
  "files": {},
  "form": {},
  "headers": {
    "Accept": "*/*",
    "Content-Length": "13",
    "Content-Type": "application/json",
    "Host": "localhost:8000",
    "User-Agent": "curl/8.4.0"
  "json": {
    "foo": "bar"
  "method": "POST",
  "origin": "",
  "url": "http://localhost:8000/anything"

As you can see, the response’s data field contains your request data. This feature is mandatory for testing response rules.

Modify webserver’s config

For the response tests you need to set up your web server as a proxy, forwarding the requests to httpbin. The following is an example of such a proxy setup.

Before you start to change your configurations, please make a backup!

Apache httpd

Put this snippet into your httpd’s default config (eg. /etc/apache2/sites-enabled/000-default.conf):

        ProxyPreserveHost On
        ProxyPass /
        ProxyPassReverse /
        ServerName localhost


Put this snippet into the nginx default config (e.g., /etc/nginx/conf.d/default.conf) or replace the existing one:

        location / {

                proxy_set_header Host $host;
                proxy_set_header Proxy "";
                proxy_set_header Upgrade $http_upgrade;
                proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
                proxy_set_header X-Forwarded-Port $server_port;
                proxy_set_header X-Forwarded-Proto $scheme;

                proxy_http_version 1.1;
                proxy_buffering off;
                proxy_connect_timeout 60s;
                proxy_read_timeout 36000s;
                proxy_redirect off;

                proxy_pass_header Authorization;

In both cases (Apache httpd, nginx) you have to change your modsecurity.conf settings. Open that file and find the directive SecResponseBodyMimeType. Modify the arguments:

SecResponseBodyMimeType text/plain text/html text/xml application/json

Note, that the default value does not have the MIME type application/json.

In your crs-setup.conf you need to add these extra rules (after the rule 900990):

SecAction \

SecRule REQUEST_HEADERS:X-CRS-Test "@rx ^.*$" \

Now, after restarting the web server all request will be sent to httpbin. Let’s start testing.


Tests are performed using go-ftw. We run our test suite automatically using go-ftw as part of a GitHub workflow. You can easily reproduce that locally, on your workstation.

For that you will need:

  • the CRS Git repository
  • Docker (modern versions of docker already include the compose command, if you are running an older version you also need to have docker-compose installed) OR your own environment
  • your rules and tests!

You can download pre-compiled binaries of go-ftw or build from source (requires you to have a Go environment). The pre-compiled binaries are available on GitHub. The binaries are ready to run and do not require installation.

You can also install pre-compiled binaries by using go install, if you have a Go environment:

$ go install github.com/coreruleset/go-ftw@latest

This will install the binary into your $HOME/go/bin directory. To compile go-ftw from source, run the following commands:

$ git clone https://github.com/coreruleset/go-ftw.git
$ cd go-ftw
$ go build

This will build the binary in the go-ftw repository.

Now create a configuration file. Because Apache httpd and nginx use different log file paths, and, perhaps, different ports, you may want to create two different configuration files for go-ftw. For details please read go-ftw’s documentation.

Example for nginx:

$ cat .ftw.nginx.yaml
logfile: /var/log/nginx/error.log
logmarkerheadername: X-CRS-TEST
    dest_addr: ""
    port: 8080

Example for Apache httpd:

$ cat .ftw.apache.yaml
logfile: /var/log/apache2/error.log
logmarkerheadername: X-CRS-TEST
    dest_addr: ""
    port: 80

Please verify that these settings are correct for your setup, especially the port values.

Running the test suite

Execute the following command to run the CRS test suite with go-ftw against Apache httpd:

$ ./go-ftw run --config .ftw.apache.yaml -d ../coreruleset/tests/regression/tests/
🛠️  Starting tests!
🚀 Running go-ftw!
👉 executing tests in file 911100.yaml
	running 911100-1: ✔ passed in 239.699575ms (RTT 126.721984ms)
	running 911100-2: ✔ passed in 63.339213ms (RTT 69.998361ms)
	running 911100-3: ✔ passed in 64.87875ms (RTT 71.368241ms)
	running 911100-4: ✔ passed in 77.823772ms (RTT 81.059904ms)
	running 911100-5: ✔ passed in 64.451749ms (RTT 70.403898ms)
	running 911100-6: ✔ passed in 67.774327ms (RTT 73.803885ms)
	running 911100-7: ✔ passed in 65.528094ms (RTT 72.64316ms)
	running 911100-8: ✔ passed in 66.129563ms (RTT 73.198992ms)
👉 executing tests in file 913100.yaml
	running 913100-1: ✔ passed in 71.242549ms (RTT 76.803619ms)
	running 913100-2: ✔ passed in 69.999667ms (RTT 76.617714ms)
	running 913100-3: ✔ passed in 70.200211ms (RTT 76.92281ms)
	running 913100-4: ✔ passed in 65.856005ms (RTT 73.328341ms)
	running 913100-5: ✔ passed in 66.986859ms (RTT 73.494356ms)

To run the test suite against nginx, execute the following:

$ ./go-ftw run --config .ftw.nginx.yaml -d ../coreruleset/tests/regression/tests/
🛠️  Starting tests!
🚀 Running go-ftw!
👉 executing tests in file 911100.yaml
	running 911100-1: ✔ passed in 851.460335ms (RTT 292.802335ms)
	running 911100-2: ✔ passed in 53.748811ms (RTT 66.798867ms)
	running 911100-3: ✔ passed in 49.237535ms (RTT 67.964411ms)
	running 911100-4: ✔ passed in 194.935023ms (RTT 202.414171ms)
	running 911100-5: ✔ passed in 52.905305ms (RTT 66.254034ms)
	running 911100-6: ✔ passed in 52.597784ms (RTT 68.58854ms)
	running 911100-7: ✔ passed in 51.996881ms (RTT 67.496534ms)
	running 911100-8: ✔ passed in 50.804143ms (RTT 67.589557ms)
👉 executing tests in file 913100.yaml
	running 913100-1: ✔ passed in 276.383507ms (RTT 85.436758ms)
	running 913100-2: ✔ passed in 86.682684ms (RTT 69.89541ms)

If you want to run only one test, or a group of tests, you can specify that using the “include” option -i (or --include). This option takes a regular expression:

$ ./go-ftw run --config .ftw.apache.yaml -d ../coreruleset/tests/regression/tests/ -i "955100-1$"

In the above case only the test case 955100-1 will be run.

If you need to see more verbose output (e.g., to look at the requests and responses sent and received by go-ftw) you can use the --debug or --trace options:

$ ./go-ftw run --config .ftw.apache.yaml -d ../coreruleset/tests/regression/tests/ -i "955100-1$" --trace
$ ./go-ftw run --config .ftw.apache.yaml -d ../coreruleset/tests/regression/tests/ -i "955100-1$" --debug

Please note again that libmodsecurity3 is not fully compatible with ModSecurity 2, some tests can fail. If you want to ignore them, you can put the tests into a list in your config:

    dest_addr: ""
    port: 8080
    # text comes from our friends at https://github.com/digitalwave/ftwrunner
    '941190-3$': 'known MSC bug - PR #2023 (Cookie without value)'
    '941330-1$': 'know MSC bug - #2148 (double escape)'

For more information and examples, please check the go-ftw documentation.

Also please don’t forget to roll back the modifications from this guide to your WAF configuration after you’re done testing!

FTW (deprecated)

ftw is our legacy test runner, and is deprecated and no longer used for tests after CRS v3.2. Refer to this GitHub workflow if you need to use the old ftw Python version. You can easily reproduce that locally, on your workstation.

For that you will need:

  • the coreruleset git repository
  • docker and docker-compose (modern versions of docker already include compose functionality)
  • python3
  • your rules and tests!

Setting up the basic environment

I normally use pipenv whenever Python is involved. It will give you both isolation and dependencies at once. But you can use basic pip and virtualenv and the result will be the same.

For installing the python tooling, just use:

❯ pipenv install -r tests/regression/requirements.txt
Creating a virtualenv for this project...
Pipfile: /private/tmp/coreruleset/Pipfile
Using /usr/local/bin/python3 (3.9.5) to create virtualenv...
⠧ Creating virtual environment...created virtual environment CPython3.9.5.final.0-64 in 392ms
  creator CPython3Posix(dest=/Users/fzipitria/.local/share/virtualenvs/coreruleset-UNJnkEXP, clear=False, global=False)
  seeder FromAppData(download=False, pip=bundle, setuptools=bundle, wheel=bundle, via=copy, app_data_dir=/Users/fzipitria/Library/Application Support/virtualenv)
    added seed packages: pip==21.0.1, setuptools==56.0.0, wheel==0.36.2
  activators BashActivator,CShellActivator,FishActivator,PowerShellActivator,PythonActivator,XonshActivator

✔ Successfully created virtual environment!
Virtualenv location: /Users/fzipitria/.local/share/virtualenvs/coreruleset-UNJnkEXP
Creating a Pipfile for this project...
Requirements file provided! Importing into Pipfile...
Pipfile.lock not found, creating...
Locking [dev-packages] dependencies...
Locking [packages] dependencies...
Building requirements...
Resolving dependencies...
✔ Success!
Updated Pipfile.lock (02e6ae)!
Installing dependencies from Pipfile.lock (02e6ae)...
  🐍   ▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉ 17/17 — 00:00:28
To activate this project's virtualenv, run pipenv shell.
Alternatively, run a command inside the virtualenv with pipenv run.

Now we are ready to start running tests.

Running the test suite

The test suite will be run by the tool ftw, now that we started our containers.

If you used the pipenv tool for installing the module, now is time to enter the shell:

❯ py.test -vs --tb=short tests/regression/CRS_Tests.py --config=modsec2-apache --ruledir_recurse=./tests/regression/tests
============================================================================== test session starts ===============================================================================
platform darwin -- Python 3.9.5, pytest-4.6.0, py-1.10.0, pluggy-0.13.1 -- /Users/fzipitria/.local/share/virtualenvs/coreruleset-bLfwOI0B/bin/python
cachedir: .pytest_cache
rootdir: /Users/fzipitria/Workspace/OWASP/coreruleset
plugins: ftw-1.2.4
collected 2468 items

tests/regression/CRS_Tests.py::test_crs[ruleset0-933210.yaml -- 933210-1] PASSED
tests/regression/CRS_Tests.py::test_crs[ruleset1-933210.yaml -- 933210-2] PASSED
tests/regression/CRS_Tests.py::test_crs[ruleset2-933210.yaml -- 933210-3] PASSED
tests/regression/CRS_Tests.py::test_crs[ruleset3-933210.yaml -- 933210-4] PASSED
tests/regression/CRS_Tests.py::test_crs[ruleset4-933210.yaml -- 933210-5] PASSED
tests/regression/CRS_Tests.py::test_crs[ruleset5-933210.yaml -- 933210-6] PASSED
tests/regression/CRS_Tests.py::test_crs[ruleset6-933210.yaml -- 933210-7] PASSED
tests/regression/CRS_Tests.py::test_crs[ruleset7-933210.yaml -- 933210-8] PASSED
tests/regression/CRS_Tests.py::test_crs[ruleset8-933210.yaml -- 933210-9] PASSED
tests/regression/CRS_Tests.py::test_crs[ruleset9-933210.yaml -- 933210-10] PASSED
tests/regression/CRS_Tests.py::test_crs[ruleset10-933210.yaml -- 933210-11] PASSED
tests/regression/CRS_Tests.py::test_crs[ruleset11-933210.yaml -- 933210-12] PASSED
tests/regression/CRS_Tests.py::test_crs[ruleset12-933210.yaml -- 933210-13] PASSED

Couple notes here:

  • using --ruledir_recurse=./tests/regression/tests will walk over all the tests defined below that directory
  • you can test your specific file using --rule=./mytest.yaml
❯ py.test -vs --tb=short tests/regression/CRS_Tests.py --config=modsec2-apache --rule=./mytest.yaml
============================================================================== test session starts ===============================================================================
platform darwin -- Python 3.9.5, pytest-4.6.0, py-1.10.0, pluggy-0.13.1 -- /Users/fzipitria/.local/share/virtualenvs/coreruleset-bLfwOI0B/bin/python
cachedir: .pytest_cache
rootdir: /Users/fzipitria/Workspace/OWASP/coreruleset
plugins: ftw-1.2.4
collected 1 item

tests/regression/CRS_Tests.py::test_crs[ruleset0-mytest.yaml -- mytest-1] PASSED

================================================================================ warnings summary ================================================================================
  /Users/fzipitria/.local/share/virtualenvs/coreruleset-bLfwOI0B/lib/python3.9/site-packages/yaml/constructor.py:126: DeprecationWarning: Using or importing the ABCs from 'collections' instead of from 'collections.abc' is deprecated since Python 3.3, and in 3.10 it will stop working
    if not isinstance(key, collections.Hashable):

-- Docs: https://docs.pytest.org/en/latest/warnings.html
====================================================================== 1 passed, 1 warnings in 0.36 seconds ======================================================================

That’s it!

Additional tips

⚠️ If your test is not matching, you can take a peek at the modsec_audit.log file, using: sudo tail -200 tests/logs/modsec2-apache/modsec_audit.log

🔧 If you need to write a test that cannot be written using text (e.g. binary content), we prefer using encoded_request in the test, using base64 encoding


Tests are a core functionality in our ruleset. So whenever you write a rule, try to add some positive and negative tests so we won’t have surprises in the future.

Happy testing! 🎉