pySigma 0.10.10

Sigma rule processing and conversion tools

pySigma

pySigma is a python library that parses and converts Sigma rules into queries. It is a replacement for the legacy Sigma toolchain (sigmac) with a much cleaner design and is almost fully tested. Backends for support of conversion into query languages and processing pipelines for transforming rule for log data models are separated into dedicated projects to keep pySigma itself slim and vendor-agnostic. See the Related Projects section below to get an overview.

Getting Started

To start using pySigma, install it using your python package manager of choice. Examples:

pip install pysigma
pipenv install pysigma
poetry add pysigma

Documentation with some usage examples can be found here.

Autodiscovery and Migration of Backend Plugins

Previously, in order to export the objects (backends, pipelines, and validators) of the plugin, it was required to manually export them using global variables in the __init__.py file of the corresponding module. However, this manual export is no longer necessary as pySigma now employs a better mechanism for autodiscovery to locate the exported objects. Consequently, the use of global variables becomes redundant and can be eliminated. Nevertheless, to ensure compatibility with older versions of pySigma and sigma-cli, support for global variables will be retained for the time being. However, it is important to note that in a future release of pySigma, the global variables will be completely phased out.

Pipeline changes after v0.9.11

In the previous implementation, pipelines were defined as functions that returned a ProcessingPipeline object. However, this approach presented a challenge for autodiscovery because the functions lacked type hints, making it difficult to determine their return type. To address this issue, a global variable named pipelines was introduced in the __init__.py file of the plugin's pipeline module. While this workaround allowed the user to manually export the pipeline functions, it was not an ideal solution.

Following discussions here, a decision was made to introduce a class decorator that could be applied to the pipeline functions. This decorator serves two purposes: it allows the functions to be treated as pipeline objects and provides a convenient way for autodiscovery to locate them. Additionally, this approach enables a gradual migration from pipeline functions to pipeline classes without breaking backward compatibility.

By adopting this decorator-based approach, the need for global variables and manual exporting is eliminated. It simplifies the autodiscovery process and enhances code organization. It is important to note that while the previous approach of using global variables will be supported for the time being, it will eventually be phased out in a future release of pySigma.

Here is the revised example illustrating the use of the class decorator:

from sigma.pipelines.base import Pipeline

@Pipeline
def pipeline_1():
    return ProcessingPipeline(
        ... # pipeline code goes here
    )


class Pipeline_2(Pipeline):
    def apply(self):
        return ProcessingPipeline(
            ... # pipeline code goes here
        )

Both pipelines can still be used in the same manner as before. There is no difference between the two approaches because the Pipeline_2 class can be instantiated and used as a pipeline object, like Pipeline_2()() or Pipeline_2().apply(). In other words, when the class is instantiated, an object of the Pipeline class is returned. Calling the object itself will automatically run the apply method, which returns a ProcessingPipeline object. This behavior aligns with the functionality of the pipeline_1 function, which also returns a ProcessingPipeline object. This consistency results in a cleaner and more streamlined approach for autodiscovery and facilitates the gradual migration of pipeline functions to classes.

pySigma before v0.9.11

The backend plugin autodiscovery functionality has been added, eliminating the need for manual registration of plugins in sigma-cli. However, some backends may not function with the updated sigma-cli version. To address this issue, plugin developers should make the following changes to their backends:

1. In the sigma/backends/my_awesome_backend/__init__.py file, add a backends global variable that references the backend class:

   from .my_awesome_backend import MyAwesomeBackend
   
   backends = {
       "my_awesome_backend": MyAwesomeBackend,
   }
   

2. In the sigma/pipelines/my_awesome_pipelines/__init__.py file, add a pipelines global variable that lists the available pipelines:

   from .my_awesome_pipelines import pipeline_1, pipeline_2
   
   pipelines = {
       "pipeline_1": pipeline_1,
       "pipeline_2": pipeline_2,
   }
   

3. (Optional) If your backend has Validators (used with sigma check): In the sigma/pipelines/my_awesome_validators/__init__.py file, add a validators global variable that lists the available pipelines:

   validators = {
       "validator_1": MyFirstValidator,
       "validator_2": MySecondValidator,
   }
   

4. Finally, submit a pull request to the pySigma-plugin-directory and update the version compatibility of your backend plugin with pySigma.

By following these steps, your backend plugin will be compatible with newer versions of pySigma and sigma-cli, allowing for autodiscovery and migration of backend plugins.

Create Your Own Backend for pySigma

The creation of a backend has become much easier with pySigma. We recommend using the "Cookie Cutter Template" and reviewing the existing backends listed in the "Related Projects" section of this README.

pySigma Cookie Cutter Template

Features

pySigma brings a number of additional features compared to sigmac, as well as some changes.

Modifier comparison between pySigma and sigmac

Modifier	Use	sigmac legacy
contains	the value is matched anywhere in the field (strings and regular expressions)	X
startswith	The value is expected at the beginning of the field's content (strings and regular expressions)	X
endswith	The value is expected at the end of the field's content (strings and regular expressions)	X
exists	The field exists (yes/true) in the matched event or doesn't exist (no/false)
base64	The value is encoded with Base64	X
base64offset	If a value might appear somewhere in a base64-encoded value the representation might change depending on the position in the overall value	X
wide	transforms value to UTF16-LE encoding	X
re	value is handled as regular expression by backends	X
i	Regular expression ignore case modifier
ignorecase	Regular expression ignore case modifier
m	Regular expression multiline modifier
multiline	Regular expression multiline modifier
s	Regular expression dot matches all modifier
dotall	Regular expression dot matches all modifier
cidr	value is handled as an IPv4 CIDR by backends
all	This modifier changes OR logic to AND	X
lt	Field is less than the value
lte	Field is less or egal than the value
gt	Field is Greater than the value
gte	Field is Greater or egal than the value
expand	Modifier for expansion of placeholders in values. It replaces placeholder strings (%something%)

Backends comparison between pySigma and sigmac

On 2022/04/10

sigmac Backends	Observation	pySigma
ala	Azure Log Analytics Queries
ala-rule	Azure Log Analytics Rule
arcsight	ArcSight saved search
arcsight-esm	ArcSight ESM saved search
athena	SQL query
carbonblack	Converts Sigma rule into CarbonBlack query string
chronicle	Google Chronicle YARA-L
crowdstrike	CrowdStrike Search Processing Language (SPL)	pySigma-pipeline-crowdstrike
csharp	CSharp Regex in LINQ query
datadog-logs	Datadog log search query
devo	Devo query
ee-outliers	ee-outliers
elastalert	ElastAlert QS query
elastalert-dsl	ElastAlert DSL query
es-dsl	Elasticsearch DSL query	pySigma-backend-elasticsearch
es-eql	Elasticsearch EQL query
es-qs	Elasticsearch query string. Only searches, no aggregations	pySigma-backend-elasticsearch
es-qs-lr	Lucene query string for LogRhythm. Only searches, no aggregations
es-rule	Elastic SIEM lucene query
es-rule-eql	Elastic SIEM EQL query
fieldlist	List all fieldnames from given Sigma rules for creation of a field mapping configuration
fireeye-helix	FireEye Helix Query Language
fortisiem	Base class for Fortisem backends that generate one text-based expression from a Sigma rule
graylog	Graylog query string. Only searches, no aggregations
grep	Generates Perl compatible regular expressions and puts 'grep -P' around it
hawk	HAWK search
humio	Humio query
kibana	Kibana JSON Configuration files (searches only)
kibana-ndjson	Kibana JSON Configuration files (searches only)	pySigma-backend-elasticsearch
lacework	Lacework Policy Platform
limacharlie	LimaCharlie D&R rules
logiq	LOGIQ event rule api payload
logpoint	LogPoint query
mdatp	Microsoft Defender ATP Hunting Queries	pySigma-backend-microsoft365defender
netwitness	NetWitness saved search
netwitness-epl	RSA NetWitness EPL
es-qs (proxied)	OpenSearch search query string. Only searches, no aggregations	pySigma-backend-opensearch (proxied by pySigma-backend-elasticsearch)
es-dsl (proxied)	OpenSearch DSL query	pySigma-backend-opensearch (proxied by pySigma-backend-elasticsearch)
opensearch-monitor	OpenSearch monitors and ElasticRule are in Elastic Common Schema	pySigma-backend-opensearch
powershell	PowerShell event log cmdlets	pySigma-backend-powershell
qradar	IBM Qradar AQL	pySigma-backend-QRadar-AQL
qualys	Qualys saved search
sentinel-rule	Azure Sentinel scheduled alert rule ARM template
splunk	Splunk Search Processing Language (SPL)	pySigma-backend-splunk
splunkdm	Splunk syntax leveraging Datamodel acceleration
splunkxml	XML used for Splunk Dashboard Panels
sql	SQL query
sqlite	SQL query for SQLite
stix	STIX pattern
sumologic	SumoLogic query
sumologic-cse	SumoLogic CSE query
sumologic-cse-rule	SumoLogic CSE query
sysmon	sysmon XML configuration
uberagent	uberAgent ESA Threat Detection Engine	pySigma-backend-uberAgent
xpack-watcher	X-Pack Watcher JSON for alerting

Overview

Conversion Overview

Pipelines

More details are described in the documentation.

Testing

pySigma uses pytest as testing framework. Simply run pytest to run all tests. Run pytest --cov=sigma to get a coverage report.

Building

To build your own package run poetry build.

Linting

To lint the code run poetry run black. To check for linting errors run poetry run black --check.

This project also uses pre-commit, which is installed by poetry as part of dev dependencies. To install the git hooks run poetry run pre-commit install after cloning the repository and installing the dependencies.

Contributing

Pull requests are welcome. Please feel free to lodge any issues/PRs as discussion points.

This blog post by Micah Babinski explains the process from a developer's perspective.

Maintainers

The project is currently maintained by:

• Thomas Patzke [e-mail]
• François Hubaut

Related Projects

pySigma isn't a monolithic library attempting to support everything but the core. Support for target query languages and log data models is provided by additional packages that extend pySigma:

• sigma-cli: a command line interface for conversion of Sigma rules based on pySigma.
• pySigma-backend-splunk
• pySigma-pipeline-sysmon
• pySigma-pipeline-crowdstrike

All packages can also be installed from PyPI if not mentioned otherwise by the Python package manager of your choice.

License

GNU Lesser General Public License v2.1. For details, please see the full license file located here.