OWASP CRS Rules parser

Incomplete parser model and sample application for parsing Core Rule Set written in the ModSecurity DSL SecRule language. It uses the python library textX for parsing.

How to use it (CLI):

1. Install dependencies Dependencies can be installed system-wide, or just for your user (using --user).

   System-wide:

   sudo pip install secrules-parsing
   

   User:

   pip install --user secrules-parsing
   

2. Execute secrules-parser specifying the location of the files you want to scan using the -f/--files argument. This takes wildcards or individual files. $ secrules-parser -c -f /owasp-crs/rules/*.conf

3. Add flags to accomplish needed tasks:

• -h, --help:

  • Description: show the help message and exit
  • Example: $ secrules-parser -h

• -r, --regex:

  • Description: Extract regular expressions from rules file
  • Example:

  $ secrules-parser --regex -f /owasp-crs/rules/REQUEST-920-PROTOCOL-ENFORCEMENT.conf
  {"/owasp-crs/rules/REQUEST-920-PROTOCOL-ENFORCEMENT.conf": [{"920100": ["^(?i:(?:[a-z]{3,10}\\s+(?:\\w{3,7}?://[\\w\\-\\./]*(?::\\d+)?)?/[^?#]*(?:\\?[^#\\s]*)?(?:#[\\S]*)?|connect (?:\\d{1,3}\\.){3}\\d{1,3}\\.?(?::\\d+)?|options \\*)\\s+[\\w\\./]+|get /[^?#]*(?:\\?[^#\\s]*)?(?:#[\\S]*)?)$"]}, {"920120": ["(?<!&(?:[aAoOuUyY]uml)|&(?:[aAeEiIoOuU]circ)|&(?:[eEiIoOuUyY]acute)|&(?:[aAeEiIoOuU]grave)|&(?:[cC]cedil)|&(?:[aAnNoO]tilde)|&(?:amp)|&(?:apos));|['\\\"=]"]}, {"920160": ["^\\d+$"]}, {"920170": ["^(?:GET|HEAD)$"]}, {"920171": ["^(?:GET|HEAD)$"]}, {"920180": ["^POST$"]}, {"920190": ["(\\d+)\\-(\\d+)\\,"]}, {"920210": ["\\b(?:keep-alive|close),\\s?(?:keep-alive|close)\\b"]}, {"920220": ["\\%(?:(?!$|\\W)|[0-9a-fA-F]{2}|u[0-9a-fA-F]{4})"]}, {"920240": ["^(?:application\\/x-www-form-urlencoded|text\\/xml)(?:;(?:\\s?charset\\s?=\\s?[\\w\\d\\-]{1,18})?)??$"]}, {"920260": ["\\%u[fF]{2}[0-9a-fA-F]{2}"]}, {"920290": ["^$"]}, {"920310": ["^$"]}, {"920311": ["^$"]}, {"920330": ["^$"]}, {"920340": ["^0$"]}, {"920350": ["^[\\d.:]+$"]}, {"920420": ["^(?:GET|HEAD|PROPFIND|OPTIONS)$"]}, {"920440": ["\\.(.*)$"]}, {"920450": ["^.*$"]}, {"920200": ["^bytes=(?:(?:\\d+)?\\-(?:\\d+)?\\s*,?\\s*){6}"]}, {"920230": ["\\%((?!$|\\W)|[0-9a-fA-F]{2}|u[0-9a-fA-F]{4})"]}, {"920121": ["['\\\";=]"]}, {"920460": ["(?<!\\Q\\\\\\E)\\Q\\\\\\E[cdeghijklmpqwxyz123456789]"]}]}
  

• -c, --correctness:

  • Description: Check the validity of the syntax
  • Example:

  $ secrules-parser -c -f /owasp-crs/rules/REQUEST-920-PROTOCOL-ENFORCEMENT.conf
  Syntax OK: ../../../rules/REQUEST-920-PROTOCOL-ENFORCEMENT.conf
  

• -v, --verbose

  • Description: Print verbose messages
  • Example:

  $ secrules-parser -c -v -f /owasp-crs/rules/REQUEST-920-PROTOCOL-ENFORCEMENT.conf
  ...
  

• -o FILE, --output FILE

  • Description: Output results to file
  • Example:

  $ secrules-parser -c -o out.json -f /owasp-crs/rules/REQUEST-920-PROTOCOL-ENFORCEMENT.conf    
  

• --output-type github | plain

  • Description: Desired output format. Useful if running from Github Actions and you want annotated output
  • Example:

  $ secrules-parser -c --output-type github -f /owasp-crs/rules/REQUEST-920-PROTOCOL-ENFORCEMENT.conf
  

How to use it (API):

process_rules(list files)

Takes a list of file path's and returns models

import glob
import os
from secrules_parsing import parser

# Extract all of our pathing
files = glob.glob("../../rules/*.conf")
# Pass absolute paths because of module location
files = [os.path.abspath(path) for path in files]
models = parser.process_rules(files)

get_correctness(list files, list models)

import glob
import os
from secrules_parsing import parser

# Extract all of our pathing
files = glob.glob("../../rules/*.conf")
# Pass absolute paths because of module location
files = [os.path.abspath(path) for path in files]
models = parser.process_rules(files)
parser.get_correctness(files, models)

Development

If you want to modify this module, follow these steps:

1. Clone this repository: git clone git@github.com:coreruleset/secrules_parsing.git
2. Do not forget to install dependencies using uv: uv sync first!
3. Edit and change the files you want.
4. Write tests! Tests are in the tests subdirectory
5. Create a PR here, and ask for review!

Misc

To visualize the syntax tree, use:

textx visualize secrules.tx
dot -Tpng -O secrules.tx.dot

Then review the generated PNG modsec.tx.dot.png!

Please file an issue if you find a bug or you want some feature added.