Awesome Open Source
Awesome Open Source


An ffi wrapper for ModSecurity Web Application Firewall. It will need a ruleset, most likely you'll want to use OWASP ModSecurity Core Rule Set (CRS).

This gem also provides a Rack middleware which can return a 403 Forbidden response to bad requests, in many cases before your application code runs.


Install ModSecurity >= 3.0.0. This gem's native extensions will not compile without it. As of 23-Sep-2018, you may have to compile ModSecurity yourself, seems that distro packages of 3.0.0 versions are not available.

And now back to your scheduled gem installation dance. Add this line to your application's Gemfile:

gem 'rodsec'

And then execute:

$ bundle

Or install it yourself as:

$ gem install rodsec


ModSecurity config

Copy spec/config/modsecurity.conf, spec/config/crs-setup.conf, and spec/config/unicode.mapping into a config directory in your app somewhere. These are pre-configured to signal an intervention on dodgy requests or responses - the rack middleware in this gem returns a 403 "Forbidden" in those cases.

You should be able to use the config files as-is. Possibly decrease the paranoia level in crs-setup.conf from 3 to 1 or 2.

Then you'll need a ruleset - start with the OWASP CRS.

Easiest is a directory structure like this:

    # copy files from OWASP CRS rules/*

The location of your rules directory is configurable if you really need to - see comments in Rodsec::Rack source.

Take a look at the *.example files in rules/.

Copying the rules files is a manual step because you really want to have at least some idea of what rules you've activated, and how to handle false positives. Search for ModSecurity and apache or nginx and you'll get lots to read.


Now you can add a use line to your rack config. In plain rack this would be something like

use Rodsec::Rack, config: config_dir, log_blk: -> tag, str { p tag: tag, str: str }

See official Rails docs on adding rack middleware to rails.

You'll know it worked when you see "loading rules file" log messages showing up in your log_blk: lambda on application startup.


You can also use this gem without rack.

msc = do |tag, str|
  # this block will be called with log strings from ModSecurity
  puts tag, str

# load config files
rule_set = Rodsec::ReadConfig.read_config config_dir, rules_dir do |tag, str|
  p tag => str

# Now check one, or several, request/response cycles.
# You'll need a new Transaction instance for each cycle.
txn = msc, rule_set, txn_log_tag: 'my_first_transaction'
  # method calls MUST be in this order
  txn.connection! ...
  txn.uri! ...
  txn.request_headers! ...
  txn.request_body! ...
  txn.response_headers! ...
  txn.response_body! ...

rescue Rodsec::Intervention => iex
  # a good place to do some logging...
  puts iex.msi.to_h # so you can see what fields are available
  puts "http_status: #{iex.msi.status}"


Thanks to NETSTOCK for funding development.


After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to


Bug reports and pull requests are welcome on GitHub at


The gem is available as open source under the terms of the MIT License.

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