Mass Download & copy to USB device by single user

Hunt Hypothesis

A malicious insider may use T1052 to download large volumes of data and copy it to a USB device, exfiltrating sensitive information. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify and mitigate potential data theft by internal actors.

KQL Query

let Alerts = SecurityAlert
| where AlertName =~ "mass download by a single user"
| where Status != 'Resolved'
| extend ipEnt = parse_json(Entities), accountEnt = parse_json(Entities)
| mv-apply tempParams = ipEnt on (
mv-expand ipEnt
| where ipEnt.Type == "ip" 
| extend IpAddress = tostring(ipEnt.Address)
)
| mv-apply tempParams = accountEnt on (
mv-expand accountEnt
| where accountEnt.Type == "account"
| extend AADUserId = tostring(accountEnt.AadUserId)
)
| extend Alert_TimeGenerated = TimeGenerated
| distinct Alert_TimeGenerated, IpAddress, AADUserId, DisplayName, Description, ProductName, ExtendedProperties, Entities, Status, CompromisedEntity
;
let CA_Events = CloudAppEvents
| where ActionType == "FileDownloaded"
| extend parsed = parse_json(RawEventData)
| extend UserId = tostring(parsed.UserId)
| extend FileName = tostring(parsed.SourceFileName)
| extend FileExtension = tostring(parsed.SourceFileExtension)
| summarize CloudAppEvent_StartTime = min(TimeGenerated), CloudAppEvent_EndTime = max(TimeGenerated), CloudAppEvent_Files = make_set(FileName), FileCount = dcount(FileName) by Application, AccountObjectId, UserId, IPAddress, City, CountryCode
| extend CloudAppEvents_Details = pack_all();
let CA_Alerts_Events = Alerts | join kind=inner (CA_Events)
on $left.AADUserId == $right.AccountObjectId and $left.IpAddress == $right.IPAddress
// Cloud app event comes before Alert
| where CloudAppEvent_EndTime <= Alert_TimeGenerated
| project Alert_TimeGenerated, UserId, AADUserId, IPAddress, CloudAppEvents_Details, CloudAppEvent_Files
;
// setup list to filter DeviceFileEvents for only files downloaded as indicated by CloudAppEvents
let CA_FileList = CA_Alerts_Events | project CloudAppEvent_Files;
CA_Alerts_Events
| join kind=inner ( DeviceFileEvents
| where ActionType in ("FileCreated", "FileRenamed")
| where FileName in~ (CA_FileList)
| summarize DeviceFileEvent_StartTime = min(TimeGenerated), DeviceFileEvent_EndTime = max(TimeGenerated), DeviceFileEvent_Files = make_set(FolderPath), DeviceFileEvent_FileCount = dcount(FolderPath) by InitiatingProcessAccountUpn, DeviceId, DeviceName, InitiatingProcessFolderPath, InitiatingProcessParentFileName//, InitiatingProcessCommandLine
| extend DeviceFileEvents_Details = pack_all()
) on $left.UserId == $right.InitiatingProcessAccountUpn
| where DeviceFileEvent_StartTime >= Alert_TimeGenerated
| join kind=inner (
// get device events where a USB drive was mounted
DeviceEvents
| where ActionType == "UsbDriveMounted"
| extend parsed = parse_json(AdditionalFields)
| extend USB_DriveLetter = tostring(AdditionalFields.DriveLetter), USB_ProductName = tostring(AdditionalFields.ProductName), USB_Volume = tostring(AdditionalFields.Volume)
| where isnotempty(USB_DriveLetter)
| project USB_TimeGenerated = TimeGenerated, DeviceId, USB_DriveLetter, USB_ProductName, USB_Volume
| extend USB_Details = pack_all()
)  
on DeviceId
// USB event occurs after the Alert
| where USB_TimeGenerated >= Alert_TimeGenerated
| mv-expand DeviceFileEvent_Files
| extend DeviceFileEvent_Files = tostring(DeviceFileEvent_Files)
// make sure that we only pickup the files that have the USB drive letter
| where DeviceFileEvent_Files startswith USB_DriveLetter
| summarize USB_Drive_MatchedFiles = make_set_if(DeviceFileEvent_Files, DeviceFileEvent_Files startswith USB_DriveLetter) by Alert_TimeGenerated, USB_TimeGenerated, UserId, AADUserId, DeviceId, DeviceName, IPAddress, CloudAppEvents_Details = tostring(CloudAppEvents_Details), DeviceFileEvents_Details = tostring(DeviceFileEvents_Details), USB_Details = tostring(USB_Details)
| extend InitiatingProcessFileName = tostring(split(todynamic(DeviceFileEvents_Details).InitiatingProcessFolderPath, "\\")[-1]), InitiatingProcessFolderPath = tostring(todynamic(DeviceFileEvents_Details).InitiatingProcessFolderPath)
| extend HostName = tostring(split(DeviceName, ".")[0]), DomainIndex = toint(indexof(DeviceName, '.'))
| extend HostNameDomain = iff(DeviceName != -1, substring(DeviceName, DomainIndex + 1), DeviceName)
| extend AccountName = tostring(split(UserId, "@")[0]), AccountUPNSuffix = tostring(split(UserId, "@")[1])
| project-away DomainIndex

Analytic Rule Definition

id: 6267ce44-1e9d-471b-9f1e-ae76a6b7aa84
name: Mass Download & copy to USB device by single user
description: |
  'This query looks for any mass download by a single user with possible file copy activity to a new USB drive. Malicious insiders may perform such activities that may cause harm to the organization. 
  This query could also reveal unintentional insider that had no intention of malicious activity but their actions may impact an organizations security posture.
  Reference:https://docs.microsoft.com/defender-cloud-apps/policy-template-reference'
severity: Medium
requiredDataConnectors:
  - connectorId: MicrosoftCloudAppSecurity
    dataTypes:
      - SecurityAlert
  - connectorId: MicrosoftThreatProtection
    dataTypes:
      - CloudAppEvents
      - DeviceEvents
      - DeviceFileEvents
queryFrequency: 1d
queryPeriod: 1d
triggerOperator: gt
triggerThreshold: 0
tactics:
  - Exfiltration
relevantTechniques:
  - T1052
query: |
  let Alerts = SecurityAlert
  | where AlertName =~ "mass download by a single user"
  | where Status != 'Resolved'
  | extend ipEnt = parse_json(Entities), accountEnt = parse_json(Entities)
  | mv-apply tempParams = ipEnt on (
  mv-expand ipEnt
  | where ipEnt.Type == "ip" 
  | extend IpAddress = tostring(ipEnt.Address)
  )
  | mv-apply tempParams = accountEnt on (
  mv-expand accountEnt
  | where accountEnt.Type == "account"
  | extend AADUserId = tostring(accountEnt.AadUserId)
  )
  | extend Alert_TimeGenerated = TimeGenerated
  | distinct Alert_TimeGenerated, IpAddress, AADUserId, DisplayName, Description, ProductName, ExtendedProperties, Entities, Status, CompromisedEntity
  ;
  let CA_Events = CloudAppEvents
  | where ActionType == "FileDownloaded"
  | extend parsed = parse_json(RawEventData)
  | extend UserId = tostring(parsed.UserId)
  | extend FileName = tostring(parsed.SourceFileName)
  | extend FileExtension = tostring(parsed.SourceFileExtension)
  | summarize CloudAppEvent_StartTime = min(TimeGenerated), CloudAppEvent_EndTime = max(TimeGenerated), CloudAppEvent_Files = make_set(FileName), FileCount = dcount(FileName) by Application, AccountObjectId, UserId, IPAddress, City, CountryCode
  | extend CloudAppEvents_Details = pack_all();
  let CA_Alerts_Events = Alerts | join kind=inner (CA_Events)
  on $left.AADUserId == $right.AccountObjectId and $left.IpAddress == $right.IPAddress
  // Cloud app event comes before Alert
  | where CloudAppEvent_EndTime <= Alert_TimeGenerated
  | project Alert_TimeGenerated, UserId, AADUserId, IPAddress, CloudAppEvents_Details, CloudAppEvent_Files
  ;
  // setup list to filter DeviceFileEvents for only files downloaded as indicated by CloudAppEvents
  let CA_FileList = CA_Alerts_Events | project CloudAppEvent_Files;
  CA_Alerts_Events
  | join kind=inner ( DeviceFileEvents
  | where ActionType in ("FileCreated", "FileRenamed")
  | where FileName in~ (CA_FileList)
  | summarize DeviceFileEvent_StartTime = min(TimeGenerated), DeviceFileEvent_EndTime = max(TimeGenerated), Device

Required Data Sources

Sentinel Table	Notes
`CloudAppEvents`	Ensure this data connector is enabled
`DeviceEvents`	Ensure this data connector is enabled
`DeviceFileEvents`	Ensure this data connector is enabled
`SecurityAlert`	Ensure this data connector is enabled

MITRE ATT&CK Context

Tactic: Exfiltration
Technique: T1052 — T1052

References

Source Query

False Positive Guidance

Scenario: User performs a legitimate system backup to USB drive
Description: A system administrator uses a tool like rsync or tar to back up critical system files to a USB drive as part of a scheduled maintenance task.
Filter/Exclusion: Exclude processes initiated by the root user or those associated with backup tools like rsync, tar, or backuppc.
Scenario: User copies large volumes of data for legal or compliance purposes
Description: A legal or compliance team member copies large datasets to a USB drive for an audit or e-discovery process using tools like cp, scp, or rsync.
Filter/Exclusion: Exclude processes initiated by users in the legal or compliance group, or those involving known compliance tools like eDiscovery or DataLossPrevention.
Scenario: User transfers data between internal servers using a USB drive as a temporary medium
Description: A developer or sysadmin uses a USB drive to transfer files between two internal servers during a troubleshooting or deployment process.
Filter/Exclusion: Exclude processes where the source and destination are internal servers, or where the USB device is used as a temporary transfer medium (e.g., scp over USB).
Scenario: User copies files to a USB drive for personal use (e.g., work from home setup)
Description: An employee copies work-related files to a USB drive to access them on a personal device for remote work.
Filter/Exclusion: Exclude users who are part of a remote work policy, or exclude transfers to devices that match known personal devices (e.g., using usb_device_id or device_serial).
Scenario: User runs a scheduled job that involves copying files to a USB drive for archiving
Description: A scheduled job (e