Microsoft Sentinel Analytic Rules
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NRT Multiple users email forwarded to same destination

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Id3b05727d-a8d1-477d-bbdd-d957da96ac7b
RulenameNRT Multiple users email forwarded to same destination
DescriptionIdentifies when multiple (more than one) users mailboxes are configured to forward to the same destination.

This could be an attacker-controlled destination mailbox configured to collect mail from multiple compromised user accounts.
SeverityMedium
TacticsCollection
Exfiltration
TechniquesT1114
T1020
Required data connectorsOffice365
KindNRT
Source Urihttps://github.com/Azure/Azure-Sentinel/blob/master/Detections/OfficeActivity/NRT_Office_MailForwarding.yaml
Version1.0.3
Arm template3b05727d-a8d1-477d-bbdd-d957da96ac7b.json
Deploy To Azure
OfficeActivity
| where OfficeWorkload =~ "Exchange"
| where Parameters has_any ("ForwardTo", "RedirectTo", "ForwardingSmtpAddress")
| mv-apply DynamicParameters = todynamic(Parameters) on (summarize ParsedParameters = make_bag(pack(tostring(DynamicParameters.Name), DynamicParameters.Value)))
| evaluate bag_unpack(ParsedParameters, columnsConflict='replace_source')
| extend DestinationMailAddress = tolower(case(
    isnotempty(column_ifexists("ForwardTo", "")), column_ifexists("ForwardTo", ""),
    isnotempty(column_ifexists("RedirectTo", "")), column_ifexists("RedirectTo", ""),
    isnotempty(column_ifexists("ForwardingSmtpAddress", "")), trim_start(@"smtp:", column_ifexists("ForwardingSmtpAddress", "")),
    ""))
| where isnotempty(DestinationMailAddress)
| mv-expand split(DestinationMailAddress, ";")
| extend ClientIPValues = extract_all(@'\[?(::ffff:)?(?P<IPAddress>(\d+\.\d+\.\d+\.\d+)|[^\]]+)\]?([-:](?P<Port>\d+))?', dynamic(["IPAddress", "Port"]), ClientIP)[0]
| extend ClientIP = tostring(ClientIPValues[0]), Port = tostring(ClientIPValues[1])
| summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated), DistinctUserCount = dcount(UserId), UserId = make_set(UserId, 250), Ports = make_set(Port, 250), EventCount = count() by tostring(DestinationMailAddress), ClientIP
| where DistinctUserCount > 1
| mv-expand UserId to typeof(string)
version: 1.0.3
tactics:
- Collection
- Exfiltration
requiredDataConnectors:
- dataTypes:
  - OfficeActivity
  connectorId: Office365
relevantTechniques:
- T1114
- T1020
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Detections/OfficeActivity/NRT_Office_MailForwarding.yaml
description: |
  'Identifies when multiple (more than one) users mailboxes are configured to forward to the same destination.
  This could be an attacker-controlled destination mailbox configured to collect mail from multiple compromised user accounts.'  
kind: NRT
severity: Medium
metadata:
  author:
    name: Pete Bryan
  categories:
    domains:
    - Security - Threat Protection
  source:
    kind: Community
  support:
    tier: Community
id: 3b05727d-a8d1-477d-bbdd-d957da96ac7b
entityMappings:
- entityType: Account
  fieldMappings:
  - columnName: UserId
    identifier: FullName
- entityType: IP
  fieldMappings:
  - columnName: ClientIP
    identifier: Address
name: NRT Multiple users email forwarded to same destination
query: |
  OfficeActivity
  | where OfficeWorkload =~ "Exchange"
  | where Parameters has_any ("ForwardTo", "RedirectTo", "ForwardingSmtpAddress")
  | mv-apply DynamicParameters = todynamic(Parameters) on (summarize ParsedParameters = make_bag(pack(tostring(DynamicParameters.Name), DynamicParameters.Value)))
  | evaluate bag_unpack(ParsedParameters, columnsConflict='replace_source')
  | extend DestinationMailAddress = tolower(case(
      isnotempty(column_ifexists("ForwardTo", "")), column_ifexists("ForwardTo", ""),
      isnotempty(column_ifexists("RedirectTo", "")), column_ifexists("RedirectTo", ""),
      isnotempty(column_ifexists("ForwardingSmtpAddress", "")), trim_start(@"smtp:", column_ifexists("ForwardingSmtpAddress", "")),
      ""))
  | where isnotempty(DestinationMailAddress)
  | mv-expand split(DestinationMailAddress, ";")
  | extend ClientIPValues = extract_all(@'\[?(::ffff:)?(?P<IPAddress>(\d+\.\d+\.\d+\.\d+)|[^\]]+)\]?([-:](?P<Port>\d+))?', dynamic(["IPAddress", "Port"]), ClientIP)[0]
  | extend ClientIP = tostring(ClientIPValues[0]), Port = tostring(ClientIPValues[1])
  | summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated), DistinctUserCount = dcount(UserId), UserId = make_set(UserId, 250), Ports = make_set(Port, 250), EventCount = count() by tostring(DestinationMailAddress), ClientIP
  | where DistinctUserCount > 1
  | mv-expand UserId to typeof(string)  
{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "parameters": {
    "workspace": {
      "type": "String"
    }
  },
  "resources": [
    {
      "apiVersion": "2023-02-01-preview",
      "id": "[concat(resourceId('Microsoft.OperationalInsights/workspaces/providers', parameters('workspace'), 'Microsoft.SecurityInsights'),'/alertRules/3b05727d-a8d1-477d-bbdd-d957da96ac7b')]",
      "kind": "NRT",
      "name": "[concat(parameters('workspace'),'/Microsoft.SecurityInsights/3b05727d-a8d1-477d-bbdd-d957da96ac7b')]",
      "properties": {
        "alertRuleTemplateName": "3b05727d-a8d1-477d-bbdd-d957da96ac7b",
        "customDetails": null,
        "description": "'Identifies when multiple (more than one) users mailboxes are configured to forward to the same destination.\nThis could be an attacker-controlled destination mailbox configured to collect mail from multiple compromised user accounts.'\n",
        "displayName": "NRT Multiple users email forwarded to same destination",
        "enabled": true,
        "entityMappings": [
          {
            "entityType": "Account",
            "fieldMappings": [
              {
                "columnName": "UserId",
                "identifier": "FullName"
              }
            ]
          },
          {
            "entityType": "IP",
            "fieldMappings": [
              {
                "columnName": "ClientIP",
                "identifier": "Address"
              }
            ]
          }
        ],
        "OriginalUri": "https://github.com/Azure/Azure-Sentinel/blob/master/Detections/OfficeActivity/NRT_Office_MailForwarding.yaml",
        "query": "OfficeActivity\n| where OfficeWorkload =~ \"Exchange\"\n| where Parameters has_any (\"ForwardTo\", \"RedirectTo\", \"ForwardingSmtpAddress\")\n| mv-apply DynamicParameters = todynamic(Parameters) on (summarize ParsedParameters = make_bag(pack(tostring(DynamicParameters.Name), DynamicParameters.Value)))\n| evaluate bag_unpack(ParsedParameters, columnsConflict='replace_source')\n| extend DestinationMailAddress = tolower(case(\n    isnotempty(column_ifexists(\"ForwardTo\", \"\")), column_ifexists(\"ForwardTo\", \"\"),\n    isnotempty(column_ifexists(\"RedirectTo\", \"\")), column_ifexists(\"RedirectTo\", \"\"),\n    isnotempty(column_ifexists(\"ForwardingSmtpAddress\", \"\")), trim_start(@\"smtp:\", column_ifexists(\"ForwardingSmtpAddress\", \"\")),\n    \"\"))\n| where isnotempty(DestinationMailAddress)\n| mv-expand split(DestinationMailAddress, \";\")\n| extend ClientIPValues = extract_all(@'\\[?(::ffff:)?(?P<IPAddress>(\\d+\\.\\d+\\.\\d+\\.\\d+)|[^\\]]+)\\]?([-:](?P<Port>\\d+))?', dynamic([\"IPAddress\", \"Port\"]), ClientIP)[0]\n| extend ClientIP = tostring(ClientIPValues[0]), Port = tostring(ClientIPValues[1])\n| summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated), DistinctUserCount = dcount(UserId), UserId = make_set(UserId, 250), Ports = make_set(Port, 250), EventCount = count() by tostring(DestinationMailAddress), ClientIP\n| where DistinctUserCount > 1\n| mv-expand UserId to typeof(string)\n",
        "severity": "Medium",
        "suppressionDuration": "PT1H",
        "suppressionEnabled": false,
        "tactics": [
          "Collection",
          "Exfiltration"
        ],
        "techniques": [
          "T1020",
          "T1114"
        ],
        "templateVersion": "1.0.3"
      },
      "type": "Microsoft.OperationalInsights/workspaces/providers/alertRules"
    }
  ]
}