SlackAudit - User login after deactivated.

Status: available
Severity: medium
Time window: 14d
Group by: EntityUserEmail, EntityUserId
Source: github.com/Azure/Azure-Sentinel

'Detects when a Slack user account was deactivated and the same user identity later authenticated again within the detection window, which may indicate account reactivation, unauthorized access, or use of a deactivated account. Analyst triage should review the deactivation time, subsequent login time, EntityUserEmail, and EntityUserId to determine whether the login was expected. This rule uses the SlackAuditAPI connector and SlackAudit_CL data type.'

MITRE ATT&CK coverage

Tactic	Techniques
Initial Access	`T1078.004` Valid Accounts: Cloud Accounts
Persistence	`T1078.004` Valid Accounts: Cloud Accounts
Privilege Escalation	`T1078.004` Valid Accounts: Cloud Accounts

Rule body

id: e6e99dcb-4dff-48d2-8012-206ca166b36b
name: SlackAudit - User login after deactivated.
description: |
  'Detects when a Slack user account was deactivated and the same user identity later authenticated again within
  the detection window, which may indicate account reactivation, unauthorized access, or use of a deactivated account. Analyst
  triage should review the deactivation time, subsequent login time, EntityUserEmail, and EntityUserId to determine whether
  the login was expected. This rule uses the SlackAuditAPI connector and SlackAudit_CL data type.'
severity: Medium
status: Available
requiredDataConnectors:
  - connectorId: SlackAuditAPI
    dataTypes:
      - SlackAudit_CL
queryFrequency: 1h
queryPeriod: 14d
triggerOperator: gt
triggerThreshold: 0
tactics:
  - InitialAccess
  - Persistence
  - PrivilegeEscalation
relevantTechniques:
  - T1078
  - T1078.004
query: |
  let lbperiod_max_d = 14d;
  let lbperiod_min_d = 1d;
  let lb_time_max_h = 24h;
  SlackAudit
  | where TimeGenerated between (ago(lbperiod_max_d) .. (lbperiod_min_d))
  | where Action =~ 'user_deactivated'
  | summarize deactivation_time = max(TimeGenerated) by EntityUserEmail, EntityUserId
  | project deactivation_time, EntityUserEmail, EntityUserId
  | join (SlackAudit
        | where TimeGenerated > ago(lb_time_max_h)
        | where Action =~ 'user_login'
        | summarize new_login_time = max(TimeGenerated) by SrcUserEmail, SrcUserIdentity
        | project new_login_time, SrcUserEmail, EntityUserId = SrcUserIdentity) on EntityUserId
  | where EntityUserEmail == SrcUserEmail
  | where deactivation_time < new_login_time
  | extend AccountCustomEntity = SrcUserEmail
entityMappings:
  - entityType: Account
    fieldMappings:
      - identifier: FullName
        columnName: AccountCustomEntity
alertDetailsOverride:
  alertDisplayNameFormat: 'Slack user login after deactivation: {{AccountCustomEntity}}'
  alertDescriptionFormat: User {{AccountCustomEntity}} logged in after deactivation; review deactivation_time {{deactivation_time}}
    and new_login_time {{new_login_time}}.
customDetails:
  DeactivationTime: deactivation_time
  NewLoginTime: new_login_time
  SlackUserEmail: EntityUserEmail
  SlackUserId: EntityUserId
version: 1.0.1
kind: Scheduled

Stages and Predicates

Parameters

let lbperiod_max_d = 14d;
let lbperiod_min_d = 1d;
let lb_time_max_h = 24h;

Stage 1: `source`

SlackAudit

Stage 2: `where`

| where TimeGenerated between (ago(lbperiod_max_d) .. (lbperiod_min_d))

Stage 3: `where`

| where Action =~ 'user_deactivated'

Stage 4: `summarize`

| summarize deactivation_time = max(TimeGenerated) by EntityUserEmail, EntityUserId

Stage 5: `project`

| project deactivation_time, EntityUserEmail, EntityUserId

Stage 6: `join`

| join (SlackAudit
      | where TimeGenerated > ago(lb_time_max_h)
      | where Action =~ 'user_login'
      | summarize new_login_time = max(TimeGenerated) by SrcUserEmail, SrcUserIdentity
      | project new_login_time, SrcUserEmail, EntityUserId = SrcUserIdentity) on EntityUserId

Stage 7: `where`

| where EntityUserEmail == SrcUserEmail

Stage 8: `where`

| where deactivation_time < new_login_time

Stage 9: `extend`

| extend AccountCustomEntity = SrcUserEmail

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`Action`	eq	`user_deactivated` `user_login`	`field:"Action" kind:eq`
`EntityUserEmail`	cross_field_compare	`SrcUserEmail` transforms: `op:eq`	`field:"EntityUserEmail" kind:cross_field_compare value:"SrcUserEmail"`
`deactivation_time`	cross_field_compare	`new_login_time` transforms: `op:lt`	`field:"deactivation_time" kind:cross_field_compare value:"new_login_time"`

Output fields

These fields are emitted when the rule matches.

Field	Source
`EntityUserEmail`	`project`
`EntityUserId`	`project`
`deactivation_time`	`project`
`AccountCustomEntity`	`extend`

SlackAudit - User login after deactivated.

MITRE ATT&CK coverage

Rule body

Stages and Predicates

Parameters

Stage 1: source

Stage 2: where

Stage 3: where

Stage 4: summarize

Stage 5: project

Stage 6: join

Stage 7: where

Stage 8: where

Stage 9: extend