Regsvr32 Rundll32 with Anomalous Parent Process

Status: available
Severity: high
Time window: 1h
Group by: DeviceName, InvestigatedProcessCommandLine, InvestigatedProcessId, InvestigatedProcessName, InvestigatedProcessStartTime
Source: github.com/Azure/Azure-Sentinel

This analytical rule looks for rundll32.exe or regsvr32.exe being spawned by abnormal processes: wscript.exe, powershell.exe, cmd.exe, pwsh.exe, cscript.exe. Blog: https://threathunt.blog/running-live-malware-for-threat-hunting-purposes/

MITRE ATT&CK coverage

Tactic	Techniques
Stealth	`T1218.010` System Binary Proxy Execution: Regsvr32 `T1218.011` System Binary Proxy Execution: Rundll32

Telemetry coverage

Platform	Record / event type
Microsoft Defender for Endpoint	`DeviceNetworkEvents` action `any`: Network activity
Microsoft Defender for Endpoint	`DeviceProcessEvents` action `any`: Process activity

Rule body

id: 2624fc55-0998-4897-bb48-1c6422befce4
name: Regsvr32 Rundll32 with Anomalous Parent Process
description: |
  This analytical rule looks for rundll32.exe or regsvr32.exe being spawned by abnormal processes: wscript.exe, powershell.exe, cmd.exe, pwsh.exe, cscript.exe.
  Blog: https://threathunt.blog/running-live-malware-for-threat-hunting-purposes/
severity: High
status: Available
requiredDataConnectors:
  - connectorId: MicrosoftThreatProtection
    dataTypes:
      - DeviceProcessEvents
      - DeviceNetworkEvents
queryFrequency: 1h
queryPeriod: 1h
triggerOperator: gt
triggerThreshold: 0
tactics:
  - DefenseEvasion
relevantTechniques:
  - T1218.010
  - T1218.011
tags:
  - Defense Evasion
  - Image Load
  - Regsvr32 Abuse
  - Rundll32 Abuse
query: |
  DeviceProcessEvents
  | where FileName has_any ("rundll32.exe","regsvr32.exe")
  | where InitiatingProcessFileName has_any ("wscript.exe","powershell.exe","cmd.exe","pwsh.exe","cscript.exe")
  | project TimeGenerated, DeviceName, InvestigatedProcessName=FileName, InvestigatedProcessCommandLine = ProcessCommandLine,InvestigatedProcessStartTime = ProcessCreationTime, InvestigatedProcessId = ProcessId, InitiatingProcessFileName, InitiatingProcessCommandLine, InitiatingProcessParentFileName
  | join (
  DeviceNetworkEvents
  | where InitiatingProcessFileName has_any ("rundll32.exe","regsvr32.exe")
  | where RemoteIPType == "Public"
  | project DeviceName, InvestigatedProcessName=InitiatingProcessFileName, InvestigatedProcessCommandLine = InitiatingProcessCommandLine,InvestigatedProcessStartTime = InitiatingProcessCreationTime, InvestigatedProcessId = InitiatingProcessId, LocalIP, RemoteIP, RemoteUrl
  ) on DeviceName, InvestigatedProcessCommandLine, InvestigatedProcessId, InvestigatedProcessName, InvestigatedProcessStartTime
  | project-away DeviceName1, InvestigatedProcessCommandLine1, InvestigatedProcessId1, InvestigatedProcessName1, InvestigatedProcessStartTime1
  | extend HostName = iff(DeviceName has '.', substring(DeviceName, 0, indexof(DeviceName, '.')), DeviceName)
  | extend DnsDomain = iff(DeviceName has '.', substring(DeviceName, indexof(DeviceName, '.') + 1), "")
entityMappings:
  - entityType: Host
    fieldMappings:
      - identifier: FullName
        columnName: DeviceName
      - identifier: HostName
        columnName: HostName
      - identifier: DnsDomain
        columnName: DnsDomain
  - entityType: IP
    fieldMappings:
      - identifier: Address
        columnName: LocalIP
  - entityType: IP
    fieldMappings:
      - identifier: Address
        columnName: RemoteIP
  - entityType: URL
    fieldMappings:
      - identifier: Url
        columnName: RemoteUrl
version: 1.0.0
kind: Scheduled

Stages and Predicates

Stage 1: `source`

DeviceProcessEvents

Stage 2: `where`

| where FileName has_any ("rundll32.exe","regsvr32.exe")

Stage 3: `where`

| where InitiatingProcessFileName has_any ("wscript.exe","powershell.exe","cmd.exe","pwsh.exe","cscript.exe")

Stage 4: `project`

| project TimeGenerated, DeviceName, InvestigatedProcessName=FileName, InvestigatedProcessCommandLine = ProcessCommandLine,InvestigatedProcessStartTime = ProcessCreationTime, InvestigatedProcessId = ProcessId, InitiatingProcessFileName, InitiatingProcessCommandLine, InitiatingProcessParentFileName

Stage 5: `join`

| join (
DeviceNetworkEvents
| where InitiatingProcessFileName has_any ("rundll32.exe","regsvr32.exe")
| where RemoteIPType == "Public"
| project DeviceName, InvestigatedProcessName=InitiatingProcessFileName, InvestigatedProcessCommandLine = InitiatingProcessCommandLine,InvestigatedProcessStartTime = InitiatingProcessCreationTime, InvestigatedProcessId = InitiatingProcessId, LocalIP, RemoteIP, RemoteUrl
) on DeviceName, InvestigatedProcessCommandLine, InvestigatedProcessId, InvestigatedProcessName, InvestigatedProcessStartTime

Stage 6: `project-away`

| project-away DeviceName1, InvestigatedProcessCommandLine1, InvestigatedProcessId1, InvestigatedProcessName1, InvestigatedProcessStartTime1

Stage 7: `extend`

| extend HostName = iff(DeviceName has '.', substring(DeviceName, 0, indexof(DeviceName, '.')), DeviceName)

HostName =

ifDeviceName has "."substring(DeviceName, 0, indexof(DeviceName, '.'))

elseDeviceName

Stage 8: `extend`

| extend DnsDomain = iff(DeviceName has '.', substring(DeviceName, indexof(DeviceName, '.') + 1), "")

DnsDomain =

ifDeviceName has "."substring(DeviceName, (indexof(DeviceName, '.') + 1))

else""

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`FileName`	match	`regsvr32.exe` transforms: `term` `rundll32.exe` transforms: `term`	`field:"file_name" kind:match`
`InitiatingProcessFileName`	match	`cmd.exe` transforms: `term` corpus 2 (kusto 2) `cscript.exe` transforms: `term` `powershell.exe` transforms: `term` corpus 2 (kusto 2) `pwsh.exe` transforms: `term` `regsvr32.exe` transforms: `term` corpus 2 (kusto 2) `rundll32.exe` transforms: `term` corpus 2 (kusto 2) `wscript.exe` transforms: `term`	`field:"parent_process_name" kind:match`
`RemoteIPType`	eq	`Public` corpus 5 (kusto 5)	`field:"RemoteIPType" kind:eq value:"Public"`

Output fields

These fields are emitted when the rule matches.

Field	Source
`DeviceName`	`project`
`InitiatingProcessCommandLine`	`project`
`InitiatingProcessFileName`	`project`
`InitiatingProcessParentFileName`	`project`
`InvestigatedProcessCommandLine`	`project`
`InvestigatedProcessId`	`project`
`InvestigatedProcessName`	`project`
`InvestigatedProcessStartTime`	`project`
`TimeGenerated`	`project`
`HostName`	`extend`
`DnsDomain`	`extend`

Regsvr32 Rundll32 with Anomalous Parent Process

MITRE ATT&CK coverage

Telemetry coverage

Rule body

Stages and Predicates

Stage 1: source

Stage 2: where

Stage 3: where

Stage 4: project

Stage 5: join

Stage 6: project-away

Stage 7: extend

Stage 8: extend