Example Scan Operator

KQL detection rule by ep3p · MIT

Notice that x = 15 does not have a state whose "parent step" is step 3 . But 11, 12, 13, 14, 16 do. This is because 14 had evaluated step 2 successfully, so in the next event (15) the state from step 2 will take precedence over the state from step 3, and this one will disappear.

// Notice that x = 15 does not have a state whose "parent step" is step 3 . But 11, 12, 13, 14, 16 do.
// This is because 14 had evaluated step 2 successfully, so in the next event (15) the state from step 2 will take precedence over the state from step 3, and this one will disappear.
let threshold = 5;
let _Range =
    range x from 1 to 16 step 1
    | extend ToBeCounted = not(x between (4 .. 6))
;
let _ScanResults =
    _Range
    | scan declare (ScanStep:long=0, ParentStep:long=0, Count:long=0, SurpassedThreshold:bool=false) with
    (
        step Step1: // output=none:
            ToBeCounted
            =>  ScanStep = 1,
                Count = Step1.Count + 1,
                ParentStep = iff(Step1.Count == 0, int(null), 1)
        ;
        step Step2:
            ToBeCounted and Step1.Count >= threshold
            =>  ScanStep = 2,
                Count = Step1.Count,
                SurpassedThreshold = true,
                ParentStep = iff(Step2.ParentStep == 0, 1, 2)
        ;
        step Step3:
            ToBeCounted and Step1.Count >= threshold
            =>  ScanStep = 3,
                Count = Step2.Count,
                SurpassedThreshold = true,
                ParentStep = iff(Step3.ParentStep == 0, 2, 3)
        ;
    )
;
_Range
| lookup _ScanResults on x, ToBeCounted
| sort by x asc, ScanStep asc
| project-reorder x, ToBeCounted, ScanStep, ParentStep

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Executable code, not a declarative rule

This submission is arbitrary [[ currentRule.format ? currentRule.format.toUpperCase() : '' ]] code, not a declarative detection rule — review it as you would any script before running it, and note that it cannot be safely aggregated or auto-executed alongside YARA/Sigma/Suricata/CRS rules.

Rejected pattern present

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