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Limit Risk Rule Score Stacking

These will help reduce the maximum amount of risk which can be added from noisy Risk Rules.

There are two methods for limiting score stacking

- Skill Level Pros Cons
Method I Beginner Easy to get started with Less context around what was capped and why
Method II Intermediate More precise deduplication and additional information Additional understanding of SPL

Method I

This caps the risk score contribution of a single source by 3x the highest score from that source.

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| tstats summariesonly=true sum(All_Risk.calculated_risk_score) as summed_risk_score max(All_Risk.calculated_risk_score) as single_risk_score dc(source) as source_count count
 FROM datamodel=Risk.All_Risk
 WHERE All_Risk.risk_object_type="*" (All_Risk.risk_object="*" OR risk_object="*")
 BY All_Risk.risk_object All_Risk.risk_object_type source
| eval capped_risk_score=if(summed_risk_score < single_risk_score*3, summed_risk_score, single_risk_score*3)
| stats sum(capped_risk_score) as capped_risk_score sum(summed_risk_score) as summed_risk_score dc(source) as source sum(count) as count
 BY All_Risk.risk_object All_Risk.risk_object_type
| sort 1000 - risk_score
...

Note

You may want to limit this to particular sources, but this is extra handy for noisy sources like EDR, DLP, or IDS.

Thanks David Dorsey!

Method II

This option adds some complexity, however, provides more information and better deduplication. The full write-up of how to accomplish this method can be found on gabs website.

Visit Website

Deduplicate Notable Events *reference: https://www.gabrielvasseur.com/post/rba-a-better-way-to-dedup-risk-events

Final SPL from blog post
| inputlookup TEMP_GABS_riskybusiness.csv
``` First we take the breakdown of what actually happened, before doing any kind of deduping ```
| eventstats sum(count) as count_msg
    by risk_object risk_object_type risk_score source risk_message ```Get breakdown per risk_message``` 
| eventstats values(eval(count_msg."*".risk_score)) as breakdown_msg
    by risk_object risk_object_type            source risk_message ```Get breakdown per risk_message```
| eventstats sum(count) as count_src
    by risk_object risk_object_type risk_score source ```Get breakdown per source```
| eventstats values(eval(count_src."*".risk_score)) as breakdown_src
    by risk_object risk_object_type            source ```Get breakdown per source```
| stats sum(count) as risk_event_count, values(breakdown_src) as breakdown_src,
    values(breakdown_msg) as breakdown_msg, sum(eval(risk_score*count)) as total_score,
    max(risk_score) as max_score, latest(_time) as _time, values(mitre_*) as mitre_*
    by risk_object risk_object_type source risk_message ```Reduce to unique risk_message
    (it's not impossible to have several risks with the same risk_message but different scores)```
| eval risk_message= mvjoin(breakdown_msg,"+")."=".max_score
    . if( total_score!=max_score, " (!" . total_score . ")", "") . " " .risk_message
``` START limit to a maximum of 10 contributions per source ```
| sort 0 risk_object risk_object_type source - max_score ``` Only the lowest scores will be dedup'd ```
| eventstats dc(risk_message) as dc_msg_per_source by risk_object risk_object_type source 
| streamstats count as rank_per_source by risk_object risk_object_type source 
| eval risk_message=case( 
    rank_per_source <= 10, risk_message,
    rank_per_source = 11, "...+" . ( dc_msg_per_source - 20 ) . " others from '" . source . "'..." ,
    1==1, null() ) 
| eval max_score=if( rank_per_source <= 10, max_score, 0 )
``` END limit to a maximum of 10 contributions per source ```
| stats sum(risk_event_count) as risk_event_count, values(breakdown_src) as breakdown_src,
    list(risk_message) as risk_message, sum(max_score) as risk_score,
    sum(total_score) as risk_score_nodedup, latest(_time) as _time, values(mitre_*) as mitre_*
    by risk_object risk_object_type source ```Reduce to unique source```
| eval breakdown_src = mvjoin(breakdown_src,"+") ."=".risk_score
    . if( risk_score!=risk_score_nodedup, " (!" . risk_score_nodedup . ")", "" ) . " ".source
| stats sum(risk_event_count) as risk_event_count, list(source) as source, dc(source) as source_count,
    list(breakdown_src) as srcs, list(risk_message) as risk_message, sum(risk_score) as risk_score,
    sum(risk_score_nodedup) as risk_score_nodedup, latest(_time) as _time, values(mitre_*) as mitre_*,
    dc( mitre_tactic_id) as mitre_tactic_id_count, dc(mitre_technique_id) as mitre_technique_id_count
    by risk_object risk_object_type ```Reduce to unique object```

Authors

@7thdrxn - Haylee Mills
@gabs - Gabriel Vasseur
Last update: May 23, 2023
Created: May 23, 2023