SlackAudit - Suspicious file downloaded

SlackAudit
| where DvcAction =~ 'file_downloaded'
| extend FileName = tostring(EntityFileName)
| extend fe = split(FileName, '.')
| extend FileExtension = iff(array_length(fe) > 1, tostring(fe[-1]), '')
| where FileName contains '.'
| where FileExtension matches regex @"^[A-Za-z]{1,4}$"
| project EntityFileName = FileName, SrcUserName
| extend AccountCustomEntity = SrcUserName
| extend FileCustomEntity = EntityFileName

entityMappings:
- entityType: Account
  fieldMappings:
  - identifier: FullName
    columnName: AccountCustomEntity
- entityType: File
  fieldMappings:
  - identifier: Name
    columnName: FileCustomEntity
name: SlackAudit - Suspicious file downloaded.
kind: Scheduled
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/SlackAudit/Analytic%20Rules/SlackAuditSuspiciousFileDownloaded.yaml
triggerOperator: gt
status: Available
queryPeriod: 1h
requiredDataConnectors:
- connectorId: SlackAuditAPI
  dataTypes:
  - SlackAudit_CL
tactics:
- InitialAccess
query: |
  SlackAudit
  | where DvcAction =~ 'file_downloaded'
  | extend FileName = tostring(EntityFileName)
  | extend fe = split(FileName, '.')
  | extend FileExtension = iff(array_length(fe) > 1, tostring(fe[-1]), '')
  | where FileName contains '.'
  | where FileExtension matches regex @"^[A-Za-z]{1,4}$"
  | project EntityFileName = FileName, SrcUserName
  | extend AccountCustomEntity = SrcUserName
  | extend FileCustomEntity = EntityFileName
description: |
  'Detects potentialy suspicious downloads.'
severity: Medium
id: 132b98a5-07e9-401a-9b6f-453e52a53979
customDetails:
  FileName: EntityFileName
  UserName: SrcUserName
triggerThreshold: 0
queryFrequency: 1h
alertDetailsOverride:
  alertDescriptionFormat: A Slack audit file_downloaded event matched the suspicious extension heuristic for {{EntityFileName}} by {{SrcUserName}}.
  alertDisplayNameFormat: 'Suspicious Slack file downloaded by {{SrcUserName}}: {{EntityFileName}}'
version: 1.0.1
relevantTechniques:
- T1189

{
  "$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/132b98a5-07e9-401a-9b6f-453e52a53979')]",
      "kind": "Scheduled",
      "name": "[concat(parameters('workspace'),'/Microsoft.SecurityInsights/132b98a5-07e9-401a-9b6f-453e52a53979')]",
      "properties": {
        "alertDetailsOverride": {
          "alertDescriptionFormat": "A Slack audit file_downloaded event matched the suspicious extension heuristic for {{EntityFileName}} by {{SrcUserName}}.",
          "alertDisplayNameFormat": "Suspicious Slack file downloaded by {{SrcUserName}}: {{EntityFileName}}"
        },
        "alertRuleTemplateName": "132b98a5-07e9-401a-9b6f-453e52a53979",
        "customDetails": {
          "FileName": "EntityFileName",
          "UserName": "SrcUserName"
        },
        "description": "'Detects potentialy suspicious downloads.'\n",
        "displayName": "SlackAudit - Suspicious file downloaded.",
        "enabled": true,
        "entityMappings": [
          {
            "entityType": "Account",
            "fieldMappings": [
              {
                "columnName": "AccountCustomEntity",
                "identifier": "FullName"
              }
            ]
          },
          {
            "entityType": "File",
            "fieldMappings": [
              {
                "columnName": "FileCustomEntity",
                "identifier": "Name"
              }
            ]
          }
        ],
        "OriginalUri": "https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/SlackAudit/Analytic%20Rules/SlackAuditSuspiciousFileDownloaded.yaml",
        "query": "SlackAudit\n| where DvcAction =~ 'file_downloaded'\n| extend FileName = tostring(EntityFileName)\n| extend fe = split(FileName, '.')\n| extend FileExtension = iff(array_length(fe) > 1, tostring(fe[-1]), '')\n| where FileName contains '.'\n| where FileExtension matches regex @\"^[A-Za-z]{1,4}$\"\n| project EntityFileName = FileName, SrcUserName\n| extend AccountCustomEntity = SrcUserName\n| extend FileCustomEntity = EntityFileName\n",
        "queryFrequency": "PT1H",
        "queryPeriod": "PT1H",
        "severity": "Medium",
        "status": "Available",
        "subTechniques": [],
        "suppressionDuration": "PT1H",
        "suppressionEnabled": false,
        "tactics": [
          "InitialAccess"
        ],
        "techniques": [
          "T1189"
        ],
        "templateVersion": "1.0.1",
        "triggerOperator": "GreaterThan",
        "triggerThreshold": 0
      },
      "type": "Microsoft.OperationalInsights/workspaces/providers/alertRules"
    }
  ]
}