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

id: bff093b2-500e-4ae5-bb49-a5b1423cbd5b
requiredDataConnectors:
- dataTypes:
  - OfficeActivity (Teams)
  connectorId: Office365
name: External user added and removed in short timeframe
version: 2.1.3
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])  
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
relevantTechniques:
- T1136
tactics:
- Persistence
triggerThreshold: 0
queryPeriod: 1h
queryFrequency: 1h
severity: Low
kind: Scheduled
triggerOperator: gt
status: Available
description: |
    'This detection flags the occurrences of external user accounts that are added to a Team and then removed within one hour.'
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Microsoft 365/Analytic Rules/ExternalUserAddedRemovedInTeams.yaml

ARM