Netskope - Excessive Downloads Detection (Spike vs Baseline)

Status: available
Severity: medium
Time window: 7d
Group by: CsUsername
Source: github.com/Azure/Azure-Sentinel

Detects users with excessive download activity compared to their 7-day baseline. Triggers when current download volume exceeds 3x the average.

MITRE ATT&CK coverage

Tactic	Techniques
Collection	`T1074` Data Staged `T1530` Data from Cloud Storage

Rule body

id: dd0ebd84-ffbe-45df-848b-0615ac446b04
name: Netskope - Excessive Downloads Detection (Spike vs Baseline)
description: |
  Detects users with excessive download activity compared to their 7-day baseline. Triggers when current download volume exceeds 3x the average.
severity: Medium
status: Available
requiredDataConnectors:
  - connectorId: NetskopeWebTxConnector
    dataTypes:
      - NetskopeWebTransactions_CL
queryFrequency: 1h
queryPeriod: 7d
triggerOperator: gt
triggerThreshold: 0
tactics:
  - Exfiltration
  - Collection
relevantTechniques:
  - T1530
  - T1074
query: |
  let lookbackPeriod = 7d;
  let currentPeriod = 1h;
  let threshold = 3;
  let baseline = NetskopeWebTransactions_CL
      | where TimeGenerated between (ago(lookbackPeriod) .. ago(currentPeriod))
      | where isnotempty(CsUsername)
      | where XCsAppActivity =~ 'Download' or ScBytes > 0
      | summarize 
          BaselineAvgBytes = avg(ScBytes),
          BaselineTotalBytes = sum(ScBytes),
          BaselineCount = count()
          by CsUsername
      | extend BaselineDailyAvg = BaselineTotalBytes / 7;
  let current = NetskopeWebTransactions_CL
      | where TimeGenerated > ago(currentPeriod)
      | where isnotempty(CsUsername)
      | where XCsAppActivity =~ 'Download' or ScBytes > 0
      | summarize 
          CurrentTotalBytes = sum(ScBytes),
          CurrentCount = count(),
          Apps = make_set(XCsApp),
          Files = make_set(XCsAppObjectName)
          by CsUsername;
  current
  | join kind=inner baseline on CsUsername
  | where CurrentTotalBytes > (BaselineDailyAvg * threshold)
  | extend 
      SpikeMultiplier = round(CurrentTotalBytes / BaselineDailyAvg, 2),
      CurrentTotalMB = round(CurrentTotalBytes / 1048576.0, 2),
      BaselineDailyMB = round(BaselineDailyAvg / 1048576.0, 2)
  | project 
      TimeGenerated = now(),
      User = CsUsername,
      CurrentDownloadMB = CurrentTotalMB,
      BaselineDailyAvgMB = BaselineDailyMB,
      SpikeMultiplier,
      DownloadCount = CurrentCount,
      ApplicationsUsed = Apps,
      FilesDownloaded = Files
entityMappings:
  - entityType: Account
    fieldMappings:
      - identifier: Name
        columnName: User
version: 1.0.0
kind: Scheduled

Stages and Predicates

Parameters

let lookbackPeriod = 7d;
let currentPeriod = 1h;
let threshold = 3;

let current is inlined into the numbered stages below.

Let binding: `baseline` used in Stage 6

let baseline = NetskopeWebTransactions_CL
    | where TimeGenerated between (ago(lookbackPeriod) .. ago(currentPeriod))
    | where isnotempty(CsUsername)
    | where XCsAppActivity =~ 'Download' or ScBytes > 0
    | summarize 
        BaselineAvgBytes = avg(ScBytes),
        BaselineTotalBytes = sum(ScBytes),
        BaselineCount = count()
        by CsUsername
    | extend BaselineDailyAvg = BaselineTotalBytes / 7;

Stages 1 to 5 define let current (the rule's main pipeline source); stages 6 to 9 run on it.

Stage 1: `source`

NetskopeWebTransactions_CL

Stage 2: `where`

| where TimeGenerated > ago(currentPeriod)

Stage 3: `where`

| where isnotempty(CsUsername)

Stage 4: `where`

| where XCsAppActivity =~ 'Download' or ScBytes > 0

Stage 5: `summarize`

| summarize 
        CurrentTotalBytes = sum(ScBytes),
        CurrentCount = count(),
        Apps = make_set(XCsApp),
        Files = make_set(XCsAppObjectName)
        by CsUsername

Stage 6: `join`

current
| join kind=inner baseline on CsUsername

Stage 7: `where`

| where CurrentTotalBytes > (BaselineDailyAvg * threshold)

Stage 8: `extend`

| extend 
    SpikeMultiplier = round(CurrentTotalBytes / BaselineDailyAvg, 2),
    CurrentTotalMB = round(CurrentTotalBytes / 1048576.0, 2),
    BaselineDailyMB = round(BaselineDailyAvg / 1048576.0, 2)

Stage 9: `project`

| project 
    TimeGenerated = now(),
    User = CsUsername,
    CurrentDownloadMB = CurrentTotalMB,
    BaselineDailyAvgMB = BaselineDailyMB,
    SpikeMultiplier,
    DownloadCount = CurrentCount,
    ApplicationsUsed = Apps,
    FilesDownloaded = Files

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`CsUsername`	is_not_null	(no value, null check)	`field:"CsUsername" kind:is_not_null`
`CurrentTotalBytes`	cross_field_compare	`BaselineDailyAvg` transforms: `op:gt`, `rhs:mul:3`	`field:"CurrentTotalBytes" kind:cross_field_compare value:"BaselineDailyAvg"`
`ScBytes`	gt	`0`	`field:"ScBytes" kind:gt value:"0"`
`XCsAppActivity`	eq	`Download`	`field:"XCsAppActivity" kind:eq value:"Download"`

Output fields

These fields are emitted when the rule matches.

Field	Source
`ApplicationsUsed`	`project`
`BaselineDailyAvgMB`	`project`
`CurrentDownloadMB`	`project`
`DownloadCount`	`project`
`FilesDownloaded`	`project`
`SpikeMultiplier`	`project`
`TimeGenerated`	`project`
`User`	`project`

Netskope - Excessive Downloads Detection (Spike vs Baseline)

MITRE ATT&CK coverage

Rule body

Stages and Predicates

Parameters

Let binding: baseline used in Stage 6

Stage 1: source

Stage 2: where

Stage 3: where

Stage 4: where

Stage 5: summarize

Stage 6: join

Stage 7: where

Stage 8: extend

Stage 9: project