This documentation page describes the concepts and classes of pySigma that can be used for transformation of Sigma rules.
Sigma rules are tranformed to take care of differences between the Sigma rule and the target data model. Examples are differences in field naming schemes or value representation.
A processing pipeline has three stages:
- Rule pre-processing: transformations that are applied to the rule. Example: field name mapping, adding conditions.
- Query post-processing: transformations that are applied to the generated query. In this stage the transformaions have access to the query generated from the backend and the rule that was the source of the conversion. Example: embedding query and rule parts in a template to define custom output formats.
- Output finalization: finalizers operate on all post-processed queries to generate the final output. Example: merge all queries and add a header to the output.
Further resources:
- SigmaHQ Blog Post: Connecting Sigma Rule Sets to your Environment with Processing Pipelines
- SigmaHQ Blog Post: Introducing Query Post-Processing and Output Finalization to Processing Pipelines
Pipeline resolvers resolve identifiers and file names into a consolidated processing pipeline and take care of the appropriate ordering via the priority property that should be contained in a processing pipeline.
A processing pipeline resolver is a :py:class:`sigma.processing.resolver.ProcessingPipelineResolver` object. It is initialized with an mapping between identifiers and :py:class:`sigma.processing.pipeline.ProcessingPipeline` objects or callables that return such objects.
The method :py:meth:`sigma.processing.resolver.ProcessingPipelineResolver.resolve_pipeline` returns a ProcessingPipeline object corresponsing with the given identifier or contained in the specified YAML file. :py:meth:`sigma.processing.resolver.ProcessingPipelineResolver.resolve` returns a consolidated pipeline with the appropriate ordering as specified by the priority property of the specified pipelines.
.. autoclass:: sigma.processing.resolver.ProcessingPipelineResolver :members:
.. autoclass:: sigma.processing.pipeline.ProcessingPipeline :members:
.. autoclass:: sigma.processing.pipeline.ProcessingItem :members:
A processing pipeline can be specified as YAML file that can be loaded with ProcessingPipeline.from_yaml(yaml) or by specifying a filename to ProcessingPipelineResolver.resolve() or ProcessingPipelineResolver.resolve_pipeline().
The following items are expected on the root level of the YAML file:
- name: the name of the pipeline.
- priority: specifies the ordering of the pipeline in case multiple pipelines are concatenated. Lower priorities are used first.
- transformations: contains a list of transformation items for the rule pre-processing stage.
- postprocessing: contains a list of transformation items for the query post-processing stage.
- finalizers: contains a list of transformation items for the output finalization stage.
Some conventions used for processing pipeline priorities are:
| Priority | Description |
|---|---|
| 10 | Log source pipelines like for Sysmon. |
| 20 | Pipelines provided by backend packages that should be run before the backend pipeline. |
| 50 | Backend pipelines that are integrated in the backend and applied automatically. |
| 60 | Backend output format pipelines that are integrated in the backend and applied automatically for the asscoiated output format. |
Pipelines with the same priority are applied in the order they were provided. Pipelines without a priority are assumed to have the priority 0.
Transformation items are defined as a map as follows:
- id: the identifier of the item. This is also tracked at detection item or condition level and can be used in future conditions.
- type: the type of the transformation as specified in the identifier to class mappings below: :ref:`transformations`
- Arbitrary transformation parameters are specified at the samle level.
- rule_conditions, detection_item_conditions, field_name_conditions: conditions of the type corresponding to the name. This can be a list of unnamed conditions that are logically linked with the same operator specified in *_cond_op or named conditions that are referenced in the *_cond_expr attribute.
Conditions are specified as follows:
- type: defines the condition type. It must be one of the identifiers that are defined in :ref:`conditions`
- rule_cond_op, detection_item_cond_op, field_name_cond_op: boolean operator for the condition result. Must be one of or or and. Defaults to and. Alternatively,
- rule_cond_expr, detection_item_cond_expr, field_name_cond_expr: specify a boolean expression that references to named condition items.
- rule_cond_not, detection_item_cond_not, field_name_cond_not: if set to True, the condition result is negated.
- Arbitrary conditions parameters are specified on the same level.
Specification of an operator and expression is mutually exclusive.
Example:
name: Custom Sysmon field naming
priority: 100
transformations:
- id: field_mapping
type: field_name_mapping
mapping:
CommandLine: command_line
rule_conditions:
- type: logsource
service: sysmon.. versionadded:: 0.8.0 Field name conditions.
There are three types of conditions:
- Rule conditions are evaluated to the whole rule. They are defined in the rule_conditions attribute of a ProcessingItem. These can be applied in the rule pre-processing stage and the query post-processing stage. These conditions are evaluated for all transformations.
- Detection item conditions are evaluated for each detection item. They are defined in the detection_item_conditions attribute of a ProcessingPipeline. These can only be applied in the rule pre-processing stage. These conditions are only evaluated for transformations that operate on detection items as well as for field name transformations in the context of detection items.
- Field name conditions are evaluated for field names that can be located in detection items, in the field name list of a Sigma rule and in field name references inside of values. They are defined in the field_name_conditions attribute of detection_item_conditions attribute of a ProcessingPipeline. These can only be applied in the rule pre-processing stage and are evaluated only for transformations that operate on field names.
Conditions can be specified unnamed as list that are logically linked with the operator specified in *_condition_linking attributes or named as dict that are referenced in the *_condition_expression.
In addition to the *_conditions attributes of ProcessingPipeline objects, there are further attributes that control the condition matching behavior:
- rule_condition_linking, detection_item_condition_linking and field_name_condition_linking: one of any or all functions. Controls if one or all of the conditions from the list must match to result in an overall match.
- rule_condition_expression, detection_item_condition_expression and field_name_condition_expression: a boolean expression that references to named condition items.
- rule_condition_negation, detection_item_condition_negation and field_name_condition_negation: if set to True, the condition result is negated.
The results of the evaluatuon of different condition types are and-linked. E.g. if a processing item contains rule and field name conditions, both must evaluate to True to get the overall result of True.
| Identifier | Class |
|---|---|
| logsource | LogsourceCondition |
| contains_detection_item | RuleContainsDetectionItemCondition |
| processing_item_applied | RuleProcessingItemAppliedCondition |
| processing_state | RuleProcessingStateCondition |
| is_sigma_rule | IsSigmaRuleCondition |
| is_sigma_correlation_rule | IsSigmaCorrelationRuleCondition |
| rule_attribute | RuleAttributeCondition |
| tag | RuleTagCondition |
.. autoclass:: sigma.processing.conditions.LogsourceCondition
.. autoclass:: sigma.processing.conditions.RuleContainsDetectionItemCondition
.. autoclass:: sigma.processing.conditions.RuleProcessingItemAppliedCondition
.. autoclass:: sigma.processing.conditions.RuleProcessingStateCondition
.. autoclass:: sigma.processing.conditions.IsSigmaRuleCondition
.. autoclass:: sigma.processing.conditions.IsSigmaCorrelationRuleCondition
.. autoclass:: sigma.processing.conditions.RuleAttributeCondition
.. autoclass:: sigma.processing.conditions.RuleTagCondition
| Identifier | Class |
|---|---|
| match_string | MatchStringCondition |
| is_null | IsNullCondition |
| processing_item_applied | DetectionItemProcessingItemAppliedCondition |
| processing_state | DetectionItemProcessingStateCondition |
.. autoclass:: sigma.processing.conditions.MatchStringCondition
.. autoclass:: sigma.processing.conditions.IsNullCondition
.. autoclass:: sigma.processing.conditions.DetectionItemProcessingItemAppliedCondition
.. autoclass:: sigma.processing.conditions.DetectionItemProcessingStateCondition
| Identifier | Class |
|---|---|
| include_fields | IncludeFieldCondition |
| exclude_fields | ExcludeFieldCondition |
| processing_item_applied | FieldNameProcessingItemAppliedCondition |
| processing_state | FieldNameProcessingStateCondition |
.. autoclass:: sigma.processing.conditions.IncludeFieldCondition
.. autoclass:: sigma.processing.conditions.ExcludeFieldCondition
.. autoclass:: sigma.processing.conditions.FieldNameProcessingItemAppliedCondition
.. autoclass:: sigma.processing.conditions.FieldNameProcessingStateCondition
Base classes must be overridden to implement new conditions that can be used in processing pipelines. In addition, the new class should be mapped to an identifier. This allows to use the condition from processing pipelines defined in YAML files. The mapping is done in the dict rule_conditions or detection_item_conditions in the sigma.processing.conditions package for the respective condition types. This is not necessary for conditions that should be uses privately and not be distributed via the main pySigma distribution.
.. autoclass:: sigma.processing.conditions.RuleProcessingCondition
.. autoclass:: sigma.processing.conditions.DetectionItemProcessingCondition
.. autoclass:: sigma.processing.conditions.FieldNameProcessingCondition
.. autoclass:: sigma.processing.conditions.ValueProcessingCondition
The following transformations with their corresponding identifiers for usage in YAML-based pipeline definitions are available:
| Identifier | Class |
|---|---|
| field_name_mapping | FieldMappingTransformation |
| field_name_prefix_mapping | FieldPrefixMappingTransformation |
| field_name_transform | FieldFunctionTransformation |
| drop_detection_item | DropDetectionItemTransformation |
| field_name_suffix | AddFieldnameSuffixTransformation |
| field_name_prefix | AddFieldnamePrefixTransformation |
| wildcard_placeholders | WildcardPlaceholderTransformation |
| value_placeholders | ValueListPlaceholderTransformation |
| query_expression_placeholders | QueryExpressionPlaceholderTransformation |
| add_condition | AddConditionTransformation |
| change_logsource | ChangeLogsourceTransformation |
| add_field | AddFieldTransformation |
| remove_field | RemoveFieldTransformation |
| set_field | SetFieldTransformation |
| replace_string | ReplaceStringTransformation |
| map_string | MapStringTransformation |
| set_state | SetStateTransformation |
| regex | RegexTransformation |
| set_value | SetValueTransformation |
| convert_type | ConvertTypeTransformation |
| rule_failure | RuleFailureTransformation |
| detection_item_failure | DetectionItemFailureTransformation |
| set_custom_attribute | SetCustomAttributeTransformation |
| nest | NestedProcessingTransformation |
.. autoclass:: sigma.processing.transformations.FieldMappingTransformation
YAML example:
transformations:
type: field_name_mapping
mapping:
EventID: EventCode
CommandLine:
- command_line
- cmdlineThis shows how to map the field name EventID to EventCode and CommandLine to command_line and cmdline. For the latter, OR-conditions will be generated to match the value on both fields. This is useful if different data models are used in the same system.
.. autoclass:: sigma.processing.transformations.FieldPrefixMappingTransformation
.. autoclass:: sigma.processing.transformations.FieldFunctionTransformation
.. autoclass:: sigma.processing.transformations.DropDetectionItemTransformation
.. autoclass:: sigma.processing.transformations.AddFieldnameSuffixTransformation
.. autoclass:: sigma.processing.transformations.AddFieldnamePrefixTransformation
.. autoclass:: sigma.processing.transformations.WildcardPlaceholderTransformation
.. autoclass:: sigma.processing.transformations.ValueListPlaceholderTransformation
.. autoclass:: sigma.processing.transformations.QueryExpressionPlaceholderTransformation
.. autoclass:: sigma.processing.transformations.AddConditionTransformation
.. autoclass:: sigma.processing.transformations.ChangeLogsourceTransformation
.. autoclass:: sigma.processing.transformations.AddFieldTransformation
.. autoclass:: sigma.processing.transformations.RemoveFieldTransformation
.. autoclass:: sigma.processing.transformations.SetFieldTransformation
.. autoclass:: sigma.processing.transformations.ReplaceStringTransformation
.. autoclass:: sigma.processing.transformations.MapStringTransformation
YAML example:
transformations:
type: map_string
mapping:
value1: mapped1
value2:
- mapped2A
- mapped2B.. autoclass:: sigma.processing.transformations.SetStateTransformation
.. autoclass:: sigma.processing.transformations.RegexTransformation
.. autoclass:: sigma.processing.transformations.SetValueTransformation
.. autoclass:: sigma.processing.transformations.ConvertTypeTransformation
.. autoclass:: sigma.processing.transformations.RuleFailureTransformation
.. autoclass:: sigma.processing.transformations.DetectionItemFailureTransformation
.. autoclass:: sigma.processing.transformations.SetCustomAttributeTransformation
.. autoclass:: sigma.processing.transformations.NestedProcessingTransformation
YAML example:
transformations:
type: nest
items:
- type: field_name_mapping
mapping:
EventID: EventCode
CommandLine:
- command_line
- cmdline
- type: set_state
state: processed.. autoclass:: sigma.processing.transformations.RegexTransformation
.. autoclass:: sigma.processing.transformations.SetValueTransformation
.. autoclass:: sigma.processing.transformations.ConvertTypeTransformation
.. autoclass:: sigma.processing.transformations.SetStateTransformation
.. autoclass:: sigma.processing.transformations.RuleFailureTransformation
.. autoclass:: sigma.processing.transformations.DetectionItemFailureTransformation
.. versionadded:: 0.10.0
| Identifier | Class |
|---|---|
| embed | EmbedQueryTransformation |
| simple_template | QuerySimpleTemplateTransformation |
| template | QueryTemplateTransformation |
| json | EmbedQueryInJSONTransformation |
| replace | ReplaceQueryTransformation |
| nest | NestedQueryPostprocessingTransformation |
.. autoclass:: sigma.processing.postprocessing.EmbedQueryTransformation
.. autoclass:: sigma.processing.postprocessing.QuerySimpleTemplateTransformation
.. autoclass:: sigma.processing.postprocessing.QueryTemplateTransformation
.. autoclass:: sigma.processing.postprocessing.EmbedQueryInJSONTransformation
.. autoclass:: sigma.processing.postprocessing.ReplaceQueryTransformation
.. autoclass:: sigma.processing.postprocessing.NestedQueryPostprocessingTransformation
.. versionadded:: 0.10.0
| Identifier | Class |
|---|---|
| concat | ConcatenateQueriesFinalizer |
| template | TemplateFinalizer |
| json | JSONFinalizer |
| yaml | YAMLFinalizer |
| nested | NestedFinalizer |
.. autoclass:: sigma.processing.finalization.ConcatenateQueriesFinalizer
.. autoclass:: sigma.processing.finalization.TemplateFinalizer
.. autoclass:: sigma.processing.finalization.JSONFinalizer
.. autoclass:: sigma.processing.finalization.YAMLFinalizer
.. autoclass:: sigma.processing.finalization.NestedFinalizer
There are four transformation base classes that can be derived to implement transformations on particular parts of a Sigma rule or the whole Sigma rule:
.. autoclass:: sigma.processing.transformations.Transformation
.. autoclass:: sigma.processing.transformations.DetectionItemTransformation
.. autoclass:: sigma.processing.transformations.ValueTransformation
.. autoclass:: sigma.processing.transformations.ConditionTransformation
tbd