Detections/SecurityEvent/UserAccountAdd-Removed.yaml

id: 7efc75ce-e2a4-400f-a8b1-283d3b0f2c60
name: Account added and removed from privileged groups
description: |
  'Identifies accounts that are added to a privileged group and then quickly removed, which could be a sign of compromise.'
severity: Low
requiredDataConnectors:
  - connectorId: SecurityEvents
    dataTypes:
      - SecurityEvent
  - connectorId: WindowsSecurityEvents
    dataTypes:
      - SecurityEvent
  - connectorId: WindowsForwardedEvents
    dataTypes:
      - WindowsEvent
queryFrequency: 1d
queryPeriod: 1d
triggerOperator: gt
triggerThreshold: 0
tactics:
  - Persistence
  - PrivilegeEscalation
relevantTechniques:
  - T1098
  - T1078
query: |
  let WellKnownLocalSID = "S-1-5-32-5[0-9][0-9]$";
  let WellKnownGroupSID = "S-1-5-21-[0-9]*-[0-9]*-[0-9]*-5[0-9][0-9]$|S-1-5-21-[0-9]*-[0-9]*-[0-9]*-1102$|S-1-5-21-[0-9]*-[0-9]*-[0-9]*-1103$|S-1-5-21-[0-9]*-[0-9]*-[0-9]*-498$|S-1-5-21-[0-9]*-[0-9]*-[0-9]*-1000$";
  let AC_Add =
  (union isfuzzy=true
  (SecurityEvent
  // Event ID related to member addition.
  | where EventID in (4728, 4732,4756)
  | where TargetSid matches regex WellKnownLocalSID or TargetSid matches regex WellKnownGroupSID
  | parse EventData with * '"MemberName">' * '=' AccountAdded ",OU" *
  | where isnotempty(AccountAdded)
  | extend GroupAddedTo = TargetUserName, AddingAccount = Account
  | extend  AccountAdded_GroupAddedTo_AddingAccount = strcat(AccountAdded, "||", GroupAddedTo, "||", AddingAccount )
  | project AccountAdded_GroupAddedTo_AddingAccount, AccountAddedTime = TimeGenerated
  ),
  (WindowsEvent
  // Event ID related to member addition.
  | where EventID in (4728, 4732,4756)
  | extend TargetSid = tostring(EventData.TargetSid)
  | where TargetSid matches regex WellKnownLocalSID or TargetSid matches regex WellKnownGroupSID
  | parse EventData.MemberName with * '"MemberName">' * '=' AccountAdded ",OU" *
  | where isnotempty(AccountAdded)
  | extend TargetUserName = tostring(EventData.TargetUserName)
  | extend AddingAccount =  strcat(tostring(EventData.SubjectDomainName),"\\", tostring(EventData.SubjectUserName))
  | extend GroupAddedTo = TargetUserName
  | extend  AccountAdded_GroupAddedTo_AddingAccount = strcat(AccountAdded, "||", GroupAddedTo, "||", AddingAccount )
  | project AccountAdded_GroupAddedTo_AddingAccount, AccountAddedTime = TimeGenerated
  )
  );
  let AC_Remove =
  ( union isfuzzy=true
  (SecurityEvent
  // Event IDs related to member removal.
  | where EventID in (4729,4733,4757)
  | where TargetSid matches regex WellKnownLocalSID or TargetSid matches regex WellKnownGroupSID
  | parse EventData with * '"MemberName">' * '=' AccountRemoved ",OU" *
  | where isnotempty(AccountRemoved)
  | extend GroupRemovedFrom = TargetUserName, RemovingAccount = Account
  | extend AccountRemoved_GroupRemovedFrom_RemovingAccount = strcat(AccountRemoved, "||", GroupRemovedFrom, "||", RemovingAccount)
  | project AccountRemoved_GroupRemovedFrom_RemovingAccount, AccountRemovedTime = TimeGenerated, Computer, AccountRemoved = tolower(AccountRemoved),
  RemovingAccount, RemovingAccountLogonId = SubjectLogonId, GroupRemovedFrom = TargetUserName, TargetDomainName
  ),
  (WindowsEvent
  // Event IDs related to member removal.
  | where EventID in (4729,4733,4757)
  | extend TargetSid = tostring(EventData.TargetSid)
  | where TargetSid matches regex WellKnownLocalSID or TargetSid matches regex WellKnownGroupSID
  | parse EventData.MemberName with * '"MemberName">' * '=' AccountRemoved ",OU" *
  | where isnotempty(AccountRemoved)
  | extend TargetUserName = tostring(EventData.TargetUserName)
  | extend RemovingAccount =  strcat(tostring(EventData.SubjectDomainName),"\\", tostring(EventData.SubjectUserName))
  | extend GroupRemovedFrom = TargetUserName
  | extend AccountRemoved_GroupRemovedFrom_RemovingAccount = strcat(AccountRemoved, "||", GroupRemovedFrom, "||", RemovingAccount)
  | extend RemovedAccountLogonId= tostring(EventData.SubjectLogonId)
  | extend TargetDomainName = tostring(EventData.TargetDomainName)
  | project AccountRemoved_GroupRemovedFrom_RemovingAccount, AccountRemovedTime = TimeGenerated, Computer, AccountRemoved = tolower(AccountRemoved),
  RemovingAccount, RemovedAccountLogonId, GroupRemovedFrom = TargetUserName, TargetDomainName
  ));
  AC_Add
  | join kind = inner AC_Remove 
  on $left.AccountAdded_GroupAddedTo_AddingAccount == $right.AccountRemoved_GroupRemovedFrom_RemovingAccount
  | extend DurationinSecondAfter_Removed = datetime_diff ('second', AccountRemovedTime, AccountAddedTime)
  | where DurationinSecondAfter_Removed > 0
  | extend HostName = tostring(split(Computer, ".")[0]), DomainIndex = toint(indexof(Computer, '.'))
  | extend HostNameDomain = iff(DomainIndex != -1, substring(Computer, DomainIndex + 1), Computer)
  | extend RemovedAccountName = tostring(split(AccountRemoved, @"\")[1]), RemovedAccountNTDomain = tostring(split(AccountRemoved, @"\")[0])
  | extend RemovingAccountName = tostring(split(RemovingAccount, @"\")[1]), RemovingAccountNTDomain = tostring(split(RemovingAccount, @"\")[0])
  | project-away DomainIndex
entityMappings:
  - entityType: Account
    fieldMappings:
      - identifier: FullName
        columnName: AccountRemoved
      - identifier: Name
        columnName: RemovedAccountName
      - identifier: NTDomain
        columnName: RemovedAccountNTDomain
  - entityType: Account
    fieldMappings:
      - identifier: FullName
        columnName: RemovingAccount
      - identifier: Name
        columnName: RemovingAccountName
      - identifier: NTDomain
        columnName: RemovingAccountNTDomain
  - entityType: Host
    fieldMappings:
      - identifier: FullName
        columnName: Computer
      - identifier: HostName
        columnName: HostName
      - identifier: NTDomain
        columnName: HostNameDomain
version: 1.1.5
kind: Scheduled
metadata:
    source:
        kind: Community
    author:
        name: Microsoft Security Research
    support:
        tier: Community
    categories:
        domains: [ "Security - Others", "Identity" ]