New Windows Reserved Filenames staged on Office file services

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Id	641ecd2d-27c9-4f05-8433-8205096b09fc
Rulename	New Windows Reserved Filenames staged on Office file services
Description	This identifies new Windows Reserved Filenames on Office services like SharePoint and OneDrive in the past 7 days. It also detects when a user uploads these files to another user’s workspace, which may indicate malicious activity.
Tactics	CommandAndControl
Techniques	T1105
Required data connectors	AzureActiveDirectory
Kind	Scheduled
Source Uri	https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Global Secure Access/Hunting Queries/New_WindowsReservedFileNamesOnOfficeFileServices.yaml
Version	2.0.1
Arm template	641ecd2d-27c9-4f05-8433-8205096b09fc.json

KQL

let starttime = todatetime('{{StartTimeISO}}');
let endtime = todatetime('{{EndTimeISO}}');
let lookback = totimespan((endtime - starttime) * 7);
let Reserved = dynamic(['CON', 'PRN', 'AUX', 'NUL', 'COM1', 'COM2', 'COM3', 'COM4', 'COM5', 'COM6', 'COM7', 'COM8', 'COM9', 'LPT1', 'LPT2', 'LPT3', 'LPT4', 'LPT5', 'LPT6', 'LPT7', 'LPT8', 'LPT9']);
EnrichedMicrosoft365AuditLogs
| where TimeGenerated between (starttime .. endtime)
| extend FileName = tostring(parse_json(tostring(AdditionalProperties)).SourceFileName)
| extend ClientUserAgent = tostring(parse_json(tostring(AdditionalProperties)).ClientUserAgent)
| extend SiteUrl = tostring(parse_json(tostring(AdditionalProperties)).SiteUrl)
| where isnotempty(ObjectId)
| where ObjectId !~ FileName
| where ObjectId in (Reserved) or FileName in (Reserved)
| where ClientUserAgent !has "Mac OS"
| project TimeGenerated, Id, Workload, RecordType, Operation, UserType, UserKey, UserId, ClientIp, ClientUserAgent, SiteUrl, ObjectId, FileName
| join kind=leftanti (
    EnrichedMicrosoft365AuditLogs
    | where TimeGenerated between (ago(lookback) .. starttime)
    | extend FileName = tostring(parse_json(tostring(AdditionalProperties)).SourceFileName)
    | extend ClientUserAgent = tostring(parse_json(tostring(AdditionalProperties)).ClientUserAgent)
    | extend SiteUrl = tostring(parse_json(tostring(AdditionalProperties)).SiteUrl)
    | where isnotempty(ObjectId)
    | where ObjectId !~ FileName
    | where ObjectId in (Reserved) or FileName in (Reserved)
    | where ClientUserAgent !has "Mac OS"
    | summarize PrevSeenCount = count() by ObjectId, UserId, FileName
) on ObjectId
| extend SiteUrlUserFolder = tolower(split(SiteUrl, '/')[-2])
| extend UserIdUserFolderFormat = tolower(replace_regex(UserId, '@|\\.', '_'))
| extend UserIdDiffThanUserFolder = iff(SiteUrl has '/personal/' and SiteUrlUserFolder != UserIdUserFolderFormat, true, false)
| summarize TimeGenerated = make_list(TimeGenerated, 100000), StartTime = min(TimeGenerated), EndTime = max(TimeGenerated), Operations = make_list(Operation, 100000), UserAgents = make_list(ClientUserAgent, 100000),
    Ids = make_list(Id, 100000), SourceRelativeUrls = make_list(ObjectId, 100000), FileNames = make_list(FileName, 100000)
    by Workload, RecordType, UserType, UserKey, UserId, ClientIp, SiteUrl, ObjectId, SiteUrlUserFolder, UserIdUserFolderFormat, UserIdDiffThanUserFolder
| extend AccountName = tostring(split(UserId, "@")[0]), AccountUPNSuffix = tostring(split(UserId, "@")[1])
| extend IP_0_Address = ClientIp
| extend Account_0_Name = AccountName
| extend Account_0_UPNSuffix = AccountUPNSuffix
| extend URL_0_Url = SiteUrl

YAML

kind: Scheduled
relevantTechniques:
- T1105
entityMappings:
- entityType: IP
  fieldMappings:
  - columnName: IP_0_Address
    identifier: Address
- entityType: Account
  fieldMappings:
  - columnName: AccountName
    identifier: Name
  - columnName: AccountUPNSuffix
    identifier: UPNSuffix
- entityType: URL
  fieldMappings:
  - columnName: URL_0_Url
    identifier: Url
tactics:
- CommandAndControl
id: 641ecd2d-27c9-4f05-8433-8205096b09fc
description-detailed: |
  'Identifies when new Windows Reserved Filenames show up on Office services such as SharePoint and OneDrive in relation to the previous 7 days.
  List currently includes ''CON'', ''PRN'', ''AUX'', ''NUL'', ''COM1'', ''COM2'', ''COM3'', ''COM4'', ''COM5'', ''COM6'',
  ''COM7'', ''COM8'', ''COM9'', ''LPT1'', ''LPT2'', ''LPT3'', ''LPT4'', ''LPT5'', ''LPT6'', ''LPT7'', ''LPT8'', ''LPT9'' file extensions.
  Additionally, identifies when a given user is uploading these files to another users workspace.
  This may be indication of a staging location for malware or other malicious activity.
  References: https://docs.microsoft.com/windows/win32/fileio/naming-a-file'  
requiredDataConnectors:
- dataTypes:
  - EnrichedMicrosoft365AuditLogs
  connectorId: AzureActiveDirectory
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Global Secure Access/Hunting Queries/New_WindowsReservedFileNamesOnOfficeFileServices.yaml
description: |
    'This identifies new Windows Reserved Filenames on Office services like SharePoint and OneDrive in the past 7 days. It also detects when a user uploads these files to another user's workspace, which may indicate malicious activity.'
query: |
  let starttime = todatetime('{{StartTimeISO}}');
  let endtime = todatetime('{{EndTimeISO}}');
  let lookback = totimespan((endtime - starttime) * 7);
  let Reserved = dynamic(['CON', 'PRN', 'AUX', 'NUL', 'COM1', 'COM2', 'COM3', 'COM4', 'COM5', 'COM6', 'COM7', 'COM8', 'COM9', 'LPT1', 'LPT2', 'LPT3', 'LPT4', 'LPT5', 'LPT6', 'LPT7', 'LPT8', 'LPT9']);
  EnrichedMicrosoft365AuditLogs
  | where TimeGenerated between (starttime .. endtime)
  | extend FileName = tostring(parse_json(tostring(AdditionalProperties)).SourceFileName)
  | extend ClientUserAgent = tostring(parse_json(tostring(AdditionalProperties)).ClientUserAgent)
  | extend SiteUrl = tostring(parse_json(tostring(AdditionalProperties)).SiteUrl)
  | where isnotempty(ObjectId)
  | where ObjectId !~ FileName
  | where ObjectId in (Reserved) or FileName in (Reserved)
  | where ClientUserAgent !has "Mac OS"
  | project TimeGenerated, Id, Workload, RecordType, Operation, UserType, UserKey, UserId, ClientIp, ClientUserAgent, SiteUrl, ObjectId, FileName
  | join kind=leftanti (
      EnrichedMicrosoft365AuditLogs
      | where TimeGenerated between (ago(lookback) .. starttime)
      | extend FileName = tostring(parse_json(tostring(AdditionalProperties)).SourceFileName)
      | extend ClientUserAgent = tostring(parse_json(tostring(AdditionalProperties)).ClientUserAgent)
      | extend SiteUrl = tostring(parse_json(tostring(AdditionalProperties)).SiteUrl)
      | where isnotempty(ObjectId)
      | where ObjectId !~ FileName
      | where ObjectId in (Reserved) or FileName in (Reserved)
      | where ClientUserAgent !has "Mac OS"
      | summarize PrevSeenCount = count() by ObjectId, UserId, FileName
  ) on ObjectId
  | extend SiteUrlUserFolder = tolower(split(SiteUrl, '/')[-2])
  | extend UserIdUserFolderFormat = tolower(replace_regex(UserId, '@|\\.', '_'))
  | extend UserIdDiffThanUserFolder = iff(SiteUrl has '/personal/' and SiteUrlUserFolder != UserIdUserFolderFormat, true, false)
  | summarize TimeGenerated = make_list(TimeGenerated, 100000), StartTime = min(TimeGenerated), EndTime = max(TimeGenerated), Operations = make_list(Operation, 100000), UserAgents = make_list(ClientUserAgent, 100000),
      Ids = make_list(Id, 100000), SourceRelativeUrls = make_list(ObjectId, 100000), FileNames = make_list(FileName, 100000)
      by Workload, RecordType, UserType, UserKey, UserId, ClientIp, SiteUrl, ObjectId, SiteUrlUserFolder, UserIdUserFolderFormat, UserIdDiffThanUserFolder
  | extend AccountName = tostring(split(UserId, "@")[0]), AccountUPNSuffix = tostring(split(UserId, "@")[1])
  | extend IP_0_Address = ClientIp
  | extend Account_0_Name = AccountName
  | extend Account_0_UPNSuffix = AccountUPNSuffix
  | extend URL_0_Url = SiteUrl  
name: New Windows Reserved Filenames staged on Office file services
version: 2.0.1

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/641ecd2d-27c9-4f05-8433-8205096b09fc')]",
      "kind": "Scheduled",
      "name": "[concat(parameters('workspace'),'/Microsoft.SecurityInsights/641ecd2d-27c9-4f05-8433-8205096b09fc')]",
      "properties": {
        "alertRuleTemplateName": "641ecd2d-27c9-4f05-8433-8205096b09fc",
        "customDetails": null,
        "description": "'This identifies new Windows Reserved Filenames on Office services like SharePoint and OneDrive in the past 7 days. It also detects when a user uploads these files to another user's workspace, which may indicate malicious activity.'\n",
        "description-detailed": "'Identifies when new Windows Reserved Filenames show up on Office services such as SharePoint and OneDrive in relation to the previous 7 days.\nList currently includes ''CON'', ''PRN'', ''AUX'', ''NUL'', ''COM1'', ''COM2'', ''COM3'', ''COM4'', ''COM5'', ''COM6'',\n''COM7'', ''COM8'', ''COM9'', ''LPT1'', ''LPT2'', ''LPT3'', ''LPT4'', ''LPT5'', ''LPT6'', ''LPT7'', ''LPT8'', ''LPT9'' file extensions.\nAdditionally, identifies when a given user is uploading these files to another users workspace.\nThis may be indication of a staging location for malware or other malicious activity.\nReferences: https://docs.microsoft.com/windows/win32/fileio/naming-a-file'\n",
        "displayName": "New Windows Reserved Filenames staged on Office file services",
        "enabled": true,
        "entityMappings": [
          {
            "entityType": "IP",
            "fieldMappings": [
              {
                "columnName": "IP_0_Address",
                "identifier": "Address"
              }
            ]
          },
          {
            "entityType": "Account",
            "fieldMappings": [
              {
                "columnName": "AccountName",
                "identifier": "Name"
              },
              {
                "columnName": "AccountUPNSuffix",
                "identifier": "UPNSuffix"
              }
            ]
          },
          {
            "entityType": "URL",
            "fieldMappings": [
              {
                "columnName": "URL_0_Url",
                "identifier": "Url"
              }
            ]
          }
        ],
        "OriginalUri": "https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Global Secure Access/Hunting Queries/New_WindowsReservedFileNamesOnOfficeFileServices.yaml",
        "query": "let starttime = todatetime('{{StartTimeISO}}');\nlet endtime = todatetime('{{EndTimeISO}}');\nlet lookback = totimespan((endtime - starttime) * 7);\nlet Reserved = dynamic(['CON', 'PRN', 'AUX', 'NUL', 'COM1', 'COM2', 'COM3', 'COM4', 'COM5', 'COM6', 'COM7', 'COM8', 'COM9', 'LPT1', 'LPT2', 'LPT3', 'LPT4', 'LPT5', 'LPT6', 'LPT7', 'LPT8', 'LPT9']);\nEnrichedMicrosoft365AuditLogs\n| where TimeGenerated between (starttime .. endtime)\n| extend FileName = tostring(parse_json(tostring(AdditionalProperties)).SourceFileName)\n| extend ClientUserAgent = tostring(parse_json(tostring(AdditionalProperties)).ClientUserAgent)\n| extend SiteUrl = tostring(parse_json(tostring(AdditionalProperties)).SiteUrl)\n| where isnotempty(ObjectId)\n| where ObjectId !~ FileName\n| where ObjectId in (Reserved) or FileName in (Reserved)\n| where ClientUserAgent !has \"Mac OS\"\n| project TimeGenerated, Id, Workload, RecordType, Operation, UserType, UserKey, UserId, ClientIp, ClientUserAgent, SiteUrl, ObjectId, FileName\n| join kind=leftanti (\n    EnrichedMicrosoft365AuditLogs\n    | where TimeGenerated between (ago(lookback) .. starttime)\n    | extend FileName = tostring(parse_json(tostring(AdditionalProperties)).SourceFileName)\n    | extend ClientUserAgent = tostring(parse_json(tostring(AdditionalProperties)).ClientUserAgent)\n    | extend SiteUrl = tostring(parse_json(tostring(AdditionalProperties)).SiteUrl)\n    | where isnotempty(ObjectId)\n    | where ObjectId !~ FileName\n    | where ObjectId in (Reserved) or FileName in (Reserved)\n    | where ClientUserAgent !has \"Mac OS\"\n    | summarize PrevSeenCount = count() by ObjectId, UserId, FileName\n) on ObjectId\n| extend SiteUrlUserFolder = tolower(split(SiteUrl, '/')[-2])\n| extend UserIdUserFolderFormat = tolower(replace_regex(UserId, '@|\\\\.', '_'))\n| extend UserIdDiffThanUserFolder = iff(SiteUrl has '/personal/' and SiteUrlUserFolder != UserIdUserFolderFormat, true, false)\n| summarize TimeGenerated = make_list(TimeGenerated, 100000), StartTime = min(TimeGenerated), EndTime = max(TimeGenerated), Operations = make_list(Operation, 100000), UserAgents = make_list(ClientUserAgent, 100000),\n    Ids = make_list(Id, 100000), SourceRelativeUrls = make_list(ObjectId, 100000), FileNames = make_list(FileName, 100000)\n    by Workload, RecordType, UserType, UserKey, UserId, ClientIp, SiteUrl, ObjectId, SiteUrlUserFolder, UserIdUserFolderFormat, UserIdDiffThanUserFolder\n| extend AccountName = tostring(split(UserId, \"@\")[0]), AccountUPNSuffix = tostring(split(UserId, \"@\")[1])\n| extend IP_0_Address = ClientIp\n| extend Account_0_Name = AccountName\n| extend Account_0_UPNSuffix = AccountUPNSuffix\n| extend URL_0_Url = SiteUrl\n",
        "subTechniques": [],
        "suppressionDuration": "PT1H",
        "suppressionEnabled": false,
        "tactics": [
          "CommandAndControl"
        ],
        "techniques": [
          "T1105"
        ],
        "templateVersion": "2.0.1"
      },
      "type": "Microsoft.OperationalInsights/workspaces/providers/alertRules"
    }
  ]
}