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Detection rules › Kusto

Cisco SEG - Multiple large emails sent to external recipient

Status
available
Severity
medium
Time window
1h
Group by
SrcUserName
Source
github.com/Azure/Azure-Sentinel

'Detects possible data exfiltration.'

MITRE ATT&CK coverage

TacticTechniques
ExfiltrationT1030 Data Transfer Size Limits

Rule body kusto

id: 1399a9a5-6200-411e-8c34-ca5658754cf7
name: Cisco SEG - Multiple large emails sent to external recipient
description: |
  'Detects possible data exfiltration.'
severity: Medium
status: Available
requiredDataConnectors:
  - connectorId: CefAma
    dataTypes:
      - CommonSecurityLog
queryFrequency: 1h
queryPeriod: 1h
triggerOperator: gt
triggerThreshold: 0
tactics:
  - Exfiltration
relevantTechniques:
  - T1030
query: |
  let e_theshold = 3;
  let s_threshold = 10000000;
  CiscoSEGEvent
  | where AdditionalFields[15]['ESAMsgSize'] > s_threshold
  | where NetworkDirection =~ 'Outgoing'
  | extend rec_domain = extract(@'@(.*)', 1, DstUserName)
  | extend s_domain = extract(@'@(.*)', 1, SrcUserName)
  | where s_domain != rec_domain
  | summarize count() by SrcUserName
  | where count_ >= e_theshold
  | extend AccountCustomEntity = SrcUserName
entityMappings:
  - entityType: Account
    fieldMappings:
      - identifier: Name
        columnName: AccountCustomEntity
version: 1.0.3
kind: Scheduled

Stages and Predicates

Parameters

let e_theshold = 3;
let s_threshold = 10000000;

Stage 1: source

CiscoSEGEvent

Stage 2: where

| where AdditionalFields[15]['ESAMsgSize'] > s_threshold

Stage 3: where

| where NetworkDirection =~ 'Outgoing'

Stage 4: extend

| extend rec_domain = extract(@'@(.*)', 1, DstUserName)

Stage 5: extend

| extend s_domain = extract(@'@(.*)', 1, SrcUserName)

Stage 6: where

| where s_domain != rec_domain

Stage 7: summarize

| summarize count() by SrcUserName

Stage 8: where

| where count_ >= e_theshold

Stage 9: extend

| extend AccountCustomEntity = SrcUserName

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

FieldKindValues
ESAMsgSizegt
  • 10000000 transforms: cased
NetworkDirectioneq
  • Outgoing
count_ge
  • 3 transforms: cased
s_domainne
  • rec_domain transforms: cased

Output fields

Fields the rule emits when it matches. Chronicle authors list these in the outcome block; they appear on the detection and $risk_score drives alerting. Sentinel / Defender XDR rules build them up through project / summarize / extend stages. Sentinel maps these into alert fields via entityMappings and customDetails; Defender XDR custom detections surface them as alert fields directly.

FieldSource
SrcUserNamesummarize
AccountCustomEntityextend