Threat Essentials - Mail redirect via ExO transport rule

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Id	d7c575b2-84f5-48cb-92c5-70d7e8246284
Rulename	Threat Essentials - Mail redirect via ExO transport rule
Description	Identifies when Exchange Online transport rule configured to forward emails. This could be an adversary mailbox configured to collect mail from multiple user accounts.
Severity	Medium
Tactics	Collection Exfiltration
Techniques	T1114 T1020
Required data connectors	Office365
Kind	Scheduled
Query frequency	1d
Query period	1d
Trigger threshold	0
Trigger operator	gt
Source Uri	https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/SecurityThreatEssentialSolution/Analytic Rules/Threat_Essentials_Mail_redirect_via_ExO_transport_rule.yaml
Version	1.0.2
Arm template	d7c575b2-84f5-48cb-92c5-70d7e8246284.json

KQL

OfficeActivity
| where OfficeWorkload == "Exchange"
| where Operation in~ ("New-TransportRule", "Set-TransportRule")
| extend p = parse_json(Parameters)
| extend RuleName = case(
  Operation =~ "Set-TransportRule", tostring(OfficeObjectId),
  Operation =~ "New-TransportRule", tostring(p[1].Value),
  "Unknown"
  )
| mvexpand p
| where (p.Name =~ "BlindCopyTo" or p.Name =~ "RedirectMessageTo") and isnotempty(p.Value)
| extend RedirectTo = p.Value
| extend ClientIPOnly = case(
  ClientIP has "." and ClientIP has ":", tostring(split(ClientIP,":")[0]),
  ClientIP has "." and ClientIP has "-", tostring(split(ClientIP,"-")[0]),
  ClientIP has "[", tostring(trim_start(@'[[]',tostring(split(ClientIP,"]")[0]))),
  ClientIP
  )
| extend Port = case(
  ClientIP has "." and ClientIP has ":", (split(ClientIP,":")[1]),
  ClientIP has "." and ClientIP has "-", (split(ClientIP,"-")[1]),
  ClientIP has "[" and ClientIP has ":", tostring(split(ClientIP,"]:")[1]),
  ClientIP has "[" and ClientIP has "-", tostring(split(ClientIP,"]-")[1]),
  ClientIP
  )
| extend ClientIP = ClientIPOnly
| project TimeGenerated, RedirectTo, ClientIP, Port, UserId, Operation, RuleName
| extend Name=split(UserId, "@")[0], UPNSuffix=split(UserId, "@")[1]

YAML

relevantTechniques:
- T1114
- T1020
name: Threat Essentials - Mail redirect via ExO transport rule
requiredDataConnectors:
- dataTypes:
  - OfficeActivity
  connectorId: Office365
entityMappings:
- fieldMappings:
  - identifier: Name
    columnName: Name
  - identifier: UPNSuffix
    columnName: UPNSuffix
  entityType: Account
- fieldMappings:
  - identifier: Address
    columnName: ClientIP
  entityType: IP
triggerThreshold: 0
id: d7c575b2-84f5-48cb-92c5-70d7e8246284
tactics:
- Collection
- Exfiltration
version: 1.0.2
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/SecurityThreatEssentialSolution/Analytic Rules/Threat_Essentials_Mail_redirect_via_ExO_transport_rule.yaml
queryPeriod: 1d
kind: Scheduled
queryFrequency: 1d
severity: Medium
status: Available
description: |
  'Identifies when Exchange Online transport rule configured to forward emails.
  This could be an adversary mailbox configured to collect mail from multiple user accounts.'  
query: |
  OfficeActivity
  | where OfficeWorkload == "Exchange"
  | where Operation in~ ("New-TransportRule", "Set-TransportRule")
  | extend p = parse_json(Parameters)
  | extend RuleName = case(
    Operation =~ "Set-TransportRule", tostring(OfficeObjectId),
    Operation =~ "New-TransportRule", tostring(p[1].Value),
    "Unknown"
    )
  | mvexpand p
  | where (p.Name =~ "BlindCopyTo" or p.Name =~ "RedirectMessageTo") and isnotempty(p.Value)
  | extend RedirectTo = p.Value
  | extend ClientIPOnly = case(
    ClientIP has "." and ClientIP has ":", tostring(split(ClientIP,":")[0]),
    ClientIP has "." and ClientIP has "-", tostring(split(ClientIP,"-")[0]),
    ClientIP has "[", tostring(trim_start(@'[[]',tostring(split(ClientIP,"]")[0]))),
    ClientIP
    )
  | extend Port = case(
    ClientIP has "." and ClientIP has ":", (split(ClientIP,":")[1]),
    ClientIP has "." and ClientIP has "-", (split(ClientIP,"-")[1]),
    ClientIP has "[" and ClientIP has ":", tostring(split(ClientIP,"]:")[1]),
    ClientIP has "[" and ClientIP has "-", tostring(split(ClientIP,"]-")[1]),
    ClientIP
    )
  | extend ClientIP = ClientIPOnly
  | project TimeGenerated, RedirectTo, ClientIP, Port, UserId, Operation, RuleName
  | extend Name=split(UserId, "@")[0], UPNSuffix=split(UserId, "@")[1]  
triggerOperator: gt

ARM

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "parameters": {
    "workspace": {
      "type": "String"
    }
  },
  "resources": [
    {
      "apiVersion": "2024-01-01-preview",
      "id": "[concat(resourceId('Microsoft.OperationalInsights/workspaces/providers', parameters('workspace'), 'Microsoft.SecurityInsights'),'/alertRules/d7c575b2-84f5-48cb-92c5-70d7e8246284')]",
      "kind": "Scheduled",
      "name": "[concat(parameters('workspace'),'/Microsoft.SecurityInsights/d7c575b2-84f5-48cb-92c5-70d7e8246284')]",
      "properties": {
        "alertRuleTemplateName": "d7c575b2-84f5-48cb-92c5-70d7e8246284",
        "customDetails": null,
        "description": "'Identifies when Exchange Online transport rule configured to forward emails.\nThis could be an adversary mailbox configured to collect mail from multiple user accounts.'\n",
        "displayName": "Threat Essentials - Mail redirect via ExO transport rule",
        "enabled": true,
        "entityMappings": [
          {
            "entityType": "Account",
            "fieldMappings": [
              {
                "columnName": "Name",
                "identifier": "Name"
              },
              {
                "columnName": "UPNSuffix",
                "identifier": "UPNSuffix"
              }
            ]
          },
          {
            "entityType": "IP",
            "fieldMappings": [
              {
                "columnName": "ClientIP",
                "identifier": "Address"
              }
            ]
          }
        ],
        "OriginalUri": "https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/SecurityThreatEssentialSolution/Analytic Rules/Threat_Essentials_Mail_redirect_via_ExO_transport_rule.yaml",
        "query": "OfficeActivity\n| where OfficeWorkload == \"Exchange\"\n| where Operation in~ (\"New-TransportRule\", \"Set-TransportRule\")\n| extend p = parse_json(Parameters)\n| extend RuleName = case(\n  Operation =~ \"Set-TransportRule\", tostring(OfficeObjectId),\n  Operation =~ \"New-TransportRule\", tostring(p[1].Value),\n  \"Unknown\"\n  )\n| mvexpand p\n| where (p.Name =~ \"BlindCopyTo\" or p.Name =~ \"RedirectMessageTo\") and isnotempty(p.Value)\n| extend RedirectTo = p.Value\n| extend ClientIPOnly = case(\n  ClientIP has \".\" and ClientIP has \":\", tostring(split(ClientIP,\":\")[0]),\n  ClientIP has \".\" and ClientIP has \"-\", tostring(split(ClientIP,\"-\")[0]),\n  ClientIP has \"[\", tostring(trim_start(@'[[]',tostring(split(ClientIP,\"]\")[0]))),\n  ClientIP\n  )\n| extend Port = case(\n  ClientIP has \".\" and ClientIP has \":\", (split(ClientIP,\":\")[1]),\n  ClientIP has \".\" and ClientIP has \"-\", (split(ClientIP,\"-\")[1]),\n  ClientIP has \"[\" and ClientIP has \":\", tostring(split(ClientIP,\"]:\")[1]),\n  ClientIP has \"[\" and ClientIP has \"-\", tostring(split(ClientIP,\"]-\")[1]),\n  ClientIP\n  )\n| extend ClientIP = ClientIPOnly\n| project TimeGenerated, RedirectTo, ClientIP, Port, UserId, Operation, RuleName\n| extend Name=split(UserId, \"@\")[0], UPNSuffix=split(UserId, \"@\")[1]\n",
        "queryFrequency": "P1D",
        "queryPeriod": "P1D",
        "severity": "Medium",
        "status": "Available",
        "subTechniques": [],
        "suppressionDuration": "PT1H",
        "suppressionEnabled": false,
        "tactics": [
          "Collection",
          "Exfiltration"
        ],
        "techniques": [
          "T1020",
          "T1114"
        ],
        "templateVersion": "1.0.2",
        "triggerOperator": "GreaterThan",
        "triggerThreshold": 0
      },
      "type": "Microsoft.OperationalInsights/workspaces/providers/alertRules"
    }
  ]
}