External user added and removed in short timeframe

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Id	bff093b2-500e-4ae5-bb49-a5b1423cbd5b
Rulename	External user added and removed in short timeframe
Description	This detection flags the occurrences of external user accounts that are added to a Team and then removed within one hour.
Severity	Low
Tactics	Persistence
Techniques	T1136
Required data connectors	Office365
Kind	Scheduled
Query frequency	1h
Query period	1h
Trigger threshold	0
Trigger operator	gt
Source Uri	https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Microsoft 365/Analytic Rules/ExternalUserAddedRemovedInTeams.yaml
Version	2.1.3
Arm template	bff093b2-500e-4ae5-bb49-a5b1423cbd5b.json

KQL

let TeamsAddDel = (Op:string){
OfficeActivity
| where OfficeWorkload =~ "MicrosoftTeams"
| where Operation == Op
| where Members has ("#EXT#")
| mv-expand Members
| extend UPN = tostring(Members.UPN)
| where UPN has ("#EXT#")
| project TimeGenerated, Operation, UPN, UserId, TeamName, ClientIP
};
let TeamsAdd = TeamsAddDel("MemberAdded")
| project TimeAdded=TimeGenerated, Operation, MemberAdded = UPN, UserWhoAdded = UserId, TeamName, ClientIP;
let TeamsDel = TeamsAddDel("MemberRemoved")
| project TimeDeleted=TimeGenerated, Operation, MemberRemoved = UPN, UserWhoDeleted = UserId, TeamName, ClientIP;
TeamsAdd
| join kind=inner (TeamsDel) on $left.MemberAdded == $right.MemberRemoved
| where TimeDeleted > TimeAdded
| project TimeAdded, TimeDeleted, MemberAdded_Removed = MemberAdded, UserWhoAdded, UserWhoDeleted, TeamName, ClientIP
| extend MemberAdded_RemovedAccountName = tostring(split(MemberAdded_Removed, "@")[0]), MemberAdded_RemovedAccountUPNSuffix = tostring(split(MemberAdded_Removed, "@")[1])
| extend UserWhoAddedAccountName = tostring(split(UserWhoAdded, "@")[0]), UserWhoAddedAccountUPNSuffix = tostring(split(UserWhoAdded, "@")[1])
| extend UserWhoDeletedAccountName = tostring(split(UserWhoDeleted, "@")[0]), UserWhoDeletedAccountUPNSuffix = tostring(split(UserWhoDeleted, "@")[1])

YAML

relevantTechniques:
- T1136
name: External user added and removed in short timeframe
requiredDataConnectors:
- dataTypes:
  - OfficeActivity (Teams)
  connectorId: Office365
entityMappings:
- fieldMappings:
  - identifier: FullName
    columnName: MemberAdded_Removed
  - identifier: Name
    columnName: MemberAdded_RemovedAccountName
  - identifier: UPNSuffix
    columnName: MemberAdded_RemovedAccountUPNSuffix
  entityType: Account
- fieldMappings:
  - identifier: FullName
    columnName: UserWhoAdded
  - identifier: Name
    columnName: UserWhoAddedAccountName
  - identifier: UPNSuffix
    columnName: UserWhoAddedAccountUPNSuffix
  entityType: Account
- fieldMappings:
  - identifier: FullName
    columnName: UserWhoDeleted
  - identifier: Name
    columnName: UserWhoDeletedAccountName
  - identifier: UPNSuffix
    columnName: UserWhoDeletedAccountUPNSuffix
  entityType: Account
- fieldMappings:
  - identifier: Address
    columnName: ClientIP
  entityType: IP
triggerThreshold: 0
id: bff093b2-500e-4ae5-bb49-a5b1423cbd5b
tactics:
- Persistence
version: 2.1.3
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Microsoft 365/Analytic Rules/ExternalUserAddedRemovedInTeams.yaml
queryPeriod: 1h
kind: Scheduled
queryFrequency: 1h
severity: Low
status: Available
description: |
    'This detection flags the occurrences of external user accounts that are added to a Team and then removed within one hour.'
query: |
  let TeamsAddDel = (Op:string){
  OfficeActivity
  | where OfficeWorkload =~ "MicrosoftTeams"
  | where Operation == Op
  | where Members has ("#EXT#")
  | mv-expand Members
  | extend UPN = tostring(Members.UPN)
  | where UPN has ("#EXT#")
  | project TimeGenerated, Operation, UPN, UserId, TeamName, ClientIP
  };
  let TeamsAdd = TeamsAddDel("MemberAdded")
  | project TimeAdded=TimeGenerated, Operation, MemberAdded = UPN, UserWhoAdded = UserId, TeamName, ClientIP;
  let TeamsDel = TeamsAddDel("MemberRemoved")
  | project TimeDeleted=TimeGenerated, Operation, MemberRemoved = UPN, UserWhoDeleted = UserId, TeamName, ClientIP;
  TeamsAdd
  | join kind=inner (TeamsDel) on $left.MemberAdded == $right.MemberRemoved
  | where TimeDeleted > TimeAdded
  | project TimeAdded, TimeDeleted, MemberAdded_Removed = MemberAdded, UserWhoAdded, UserWhoDeleted, TeamName, ClientIP
  | extend MemberAdded_RemovedAccountName = tostring(split(MemberAdded_Removed, "@")[0]), MemberAdded_RemovedAccountUPNSuffix = tostring(split(MemberAdded_Removed, "@")[1])
  | extend UserWhoAddedAccountName = tostring(split(UserWhoAdded, "@")[0]), UserWhoAddedAccountUPNSuffix = tostring(split(UserWhoAdded, "@")[1])
  | extend UserWhoDeletedAccountName = tostring(split(UserWhoDeleted, "@")[0]), UserWhoDeletedAccountUPNSuffix = tostring(split(UserWhoDeleted, "@")[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/bff093b2-500e-4ae5-bb49-a5b1423cbd5b')]",
      "kind": "Scheduled",
      "name": "[concat(parameters('workspace'),'/Microsoft.SecurityInsights/bff093b2-500e-4ae5-bb49-a5b1423cbd5b')]",
      "properties": {
        "alertRuleTemplateName": "bff093b2-500e-4ae5-bb49-a5b1423cbd5b",
        "customDetails": null,
        "description": "'This detection flags the occurrences of external user accounts that are added to a Team and then removed within one hour.'\n",
        "displayName": "External user added and removed in short timeframe",
        "enabled": true,
        "entityMappings": [
          {
            "entityType": "Account",
            "fieldMappings": [
              {
                "columnName": "MemberAdded_Removed",
                "identifier": "FullName"
              },
              {
                "columnName": "MemberAdded_RemovedAccountName",
                "identifier": "Name"
              },
              {
                "columnName": "MemberAdded_RemovedAccountUPNSuffix",
                "identifier": "UPNSuffix"
              }
            ]
          },
          {
            "entityType": "Account",
            "fieldMappings": [
              {
                "columnName": "UserWhoAdded",
                "identifier": "FullName"
              },
              {
                "columnName": "UserWhoAddedAccountName",
                "identifier": "Name"
              },
              {
                "columnName": "UserWhoAddedAccountUPNSuffix",
                "identifier": "UPNSuffix"
              }
            ]
          },
          {
            "entityType": "Account",
            "fieldMappings": [
              {
                "columnName": "UserWhoDeleted",
                "identifier": "FullName"
              },
              {
                "columnName": "UserWhoDeletedAccountName",
                "identifier": "Name"
              },
              {
                "columnName": "UserWhoDeletedAccountUPNSuffix",
                "identifier": "UPNSuffix"
              }
            ]
          },
          {
            "entityType": "IP",
            "fieldMappings": [
              {
                "columnName": "ClientIP",
                "identifier": "Address"
              }
            ]
          }
        ],
        "OriginalUri": "https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Microsoft 365/Analytic Rules/ExternalUserAddedRemovedInTeams.yaml",
        "query": "let TeamsAddDel = (Op:string){\nOfficeActivity\n| where OfficeWorkload =~ \"MicrosoftTeams\"\n| where Operation == Op\n| where Members has (\"#EXT#\")\n| mv-expand Members\n| extend UPN = tostring(Members.UPN)\n| where UPN has (\"#EXT#\")\n| project TimeGenerated, Operation, UPN, UserId, TeamName, ClientIP\n};\nlet TeamsAdd = TeamsAddDel(\"MemberAdded\")\n| project TimeAdded=TimeGenerated, Operation, MemberAdded = UPN, UserWhoAdded = UserId, TeamName, ClientIP;\nlet TeamsDel = TeamsAddDel(\"MemberRemoved\")\n| project TimeDeleted=TimeGenerated, Operation, MemberRemoved = UPN, UserWhoDeleted = UserId, TeamName, ClientIP;\nTeamsAdd\n| join kind=inner (TeamsDel) on $left.MemberAdded == $right.MemberRemoved\n| where TimeDeleted > TimeAdded\n| project TimeAdded, TimeDeleted, MemberAdded_Removed = MemberAdded, UserWhoAdded, UserWhoDeleted, TeamName, ClientIP\n| extend MemberAdded_RemovedAccountName = tostring(split(MemberAdded_Removed, \"@\")[0]), MemberAdded_RemovedAccountUPNSuffix = tostring(split(MemberAdded_Removed, \"@\")[1])\n| extend UserWhoAddedAccountName = tostring(split(UserWhoAdded, \"@\")[0]), UserWhoAddedAccountUPNSuffix = tostring(split(UserWhoAdded, \"@\")[1])\n| extend UserWhoDeletedAccountName = tostring(split(UserWhoDeleted, \"@\")[0]), UserWhoDeletedAccountUPNSuffix = tostring(split(UserWhoDeleted, \"@\")[1])\n",
        "queryFrequency": "PT1H",
        "queryPeriod": "PT1H",
        "severity": "Low",
        "status": "Available",
        "subTechniques": [],
        "suppressionDuration": "PT1H",
        "suppressionEnabled": false,
        "tactics": [
          "Persistence"
        ],
        "techniques": [
          "T1136"
        ],
        "templateVersion": "2.1.3",
        "triggerOperator": "GreaterThan",
        "triggerThreshold": 0
      },
      "type": "Microsoft.OperationalInsights/workspaces/providers/alertRules"
    }
  ]
}