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Overview

DCOM (Distributed Component Object Model) is Microsoft’s technology for component-based object-oriented programming over the network. Impacket provides support for DCOM and its most common use case: Windows Management Instrumentation (WMI).

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DCOM Architecture

DCOM extends COM (Component Object Model) to support remote object creation and method invocation. Key concepts:
  • OBJREF: Object references that identify remote objects
  • IPID: Interface Pointer Identifier
  • OXID: Object Exporter Identifier
  • IRemUnknown: Base interface for remote objects

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DCOM Modules

Location: impacket/dcerpc/v5/dcom/
  • dcomrt.py - DCOM runtime and core interfaces
  • wmi.py - WMI implementation
  • oaut.py - OLE Automation types
  • vds.py - Virtual Disk Service
  • comev.py - COM Event System
  • scmp.py - DCOM System Configuration

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Windows Management Instrumentation (WMI)

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Basic WMI Query

from impacket.dcerpc.v5.dcomrt import DCOMConnection
from impacket.dcerpc.v5.dcom import wmi
from impacket.dcerpc.v5.dtypes import NULL

# Establish DCOM connection
dcom = DCOMConnection(
    '192.168.1.100',
    username='Administrator',
    password='Password123',
    domain='DOMAIN'
)

try:
    # Get WMI interface
    iInterface = dcom.CoCreateInstanceEx(wmi.CLSID_WbemLevel1Login, wmi.IID_IWbemLevel1Login)
    iWbemLevel1Login = wmi.IWbemLevel1Login(iInterface)
    
    # Login to WMI namespace
    iWbemServices = iWbemLevel1Login.NTLMLogin('//./root/cimv2', NULL, NULL)
    iWbemLevel1Login.RemRelease()
    
    # Execute WQL query
    iEnumWbemClassObject = iWbemServices.ExecQuery('SELECT * FROM Win32_Process')
    
    # Iterate through results
    while True:
        try:
            pEnum = iEnumWbemClassObject.Next(0xffffffff, 1)[0]
            record = pEnum.getProperties()
            
            print(f"Process: {record['Name']['value']}")
            print(f"  PID: {record['ProcessId']['value']}")
            print(f"  Command: {record['CommandLine']['value']}")
            print()
            
        except Exception as e:
            if 'S_FALSE' in str(e):
                break
            raise
    
finally:
    dcom.disconnect()

​
Common WMI Queries

# Operating system information
iEnum = iWbemServices.ExecQuery('SELECT * FROM Win32_OperatingSystem')
pEnum = iEnum.Next(0xffffffff, 1)[0]
record = pEnum.getProperties()
print(f"OS: {record['Caption']['value']}")
print(f"Version: {record['Version']['value']}")
print(f"Architecture: {record['OSArchitecture']['value']}")

# Computer system
iEnum = iWbemServices.ExecQuery('SELECT * FROM Win32_ComputerSystem')
pEnum = iEnum.Next(0xffffffff, 1)[0]
record = pEnum.getProperties()
print(f"Computer: {record['Name']['value']}")
print(f"Domain: {record['Domain']['value']}")
print(f"Model: {record['Model']['value']}")

# Network adapters
iEnum = iWbemServices.ExecQuery(
    'SELECT * FROM Win32_NetworkAdapterConfiguration WHERE IPEnabled = True'
)
while True:
    try:
        pEnum = iEnum.Next(0xffffffff, 1)[0]
        record = pEnum.getProperties()
        print(f"Adapter: {record['Description']['value']}")
        if record['IPAddress']['value']:
            for ip in record['IPAddress']['value']:
                print(f"  IP: {ip}")
    except:
        break

# Services
iEnum = iWbemServices.ExecQuery('SELECT * FROM Win32_Service')
while True:
    try:
        pEnum = iEnum.Next(0xffffffff, 1)[0]
        record = pEnum.getProperties()
        print(f"{record['Name']['value']}: {record['State']['value']}")
    except:
        break

# Installed software
iEnum = iWbemServices.ExecQuery('SELECT * FROM Win32_Product')
while True:
    try:
        pEnum = iEnum.Next(0xffffffff, 1)[0]
        record = pEnum.getProperties()
        print(f"{record['Name']['value']} - {record['Version']['value']}")
    except:
        break

​
Remote Command Execution via WMI

from impacket.dcerpc.v5.dcomrt import DCOMConnection
from impacket.dcerpc.v5.dcom import wmi
from impacket.dcerpc.v5.dtypes import NULL
import time

dcom = DCOMConnection('192.168.1.100', 'user', 'pass', 'DOMAIN')

try:
    iInterface = dcom.CoCreateInstanceEx(wmi.CLSID_WbemLevel1Login, wmi.IID_IWbemLevel1Login)
    iWbemLevel1Login = wmi.IWbemLevel1Login(iInterface)
    iWbemServices = iWbemLevel1Login.NTLMLogin('//./root/cimv2', NULL, NULL)
    
    # Get Win32_Process class
    processClass, _ = iWbemServices.GetObject('Win32_Process')
    
    # Create process using Create method
    command = 'cmd.exe /c ipconfig > C:\\\\output.txt'
    processClass.Create(command, NULL, NULL)
    
    print(f"Command executed: {command}")
    
    # Wait and check if process exists
    time.sleep(2)
    iEnum = iWbemServices.ExecQuery(f'SELECT * FROM Win32_Process WHERE Name="cmd.exe"')
    
finally:
    dcom.disconnect()

​
Semi-Interactive Shell via WMI

from impacket.dcerpc.v5.dcomrt import DCOMConnection
from impacket.dcerpc.v5.dcom import wmi
from impacket.dcerpc.v5.dtypes import NULL
import time
import random
import string

class WMIShell:
    def __init__(self, target, username, password, domain=''):
        self.dcom = DCOMConnection(target, username, password, domain)
        iInterface = self.dcom.CoCreateInstanceEx(wmi.CLSID_WbemLevel1Login, wmi.IID_IWbemLevel1Login)
        iWbemLevel1Login = wmi.IWbemLevel1Login(iInterface)
        self.iWbemServices = iWbemLevel1Login.NTLMLogin('//./root/cimv2', NULL, NULL)
        self.processClass, _ = self.iWbemServices.GetObject('Win32_Process')
        
    def execute(self, command):
        """Execute command and return output"""
        # Generate random filename
        output_file = ''.join(random.choice(string.ascii_letters) for _ in range(8)) + '.txt'
        output_path = f'C:\\\\Windows\\\\Temp\\\\{output_file}'
        
        # Execute command with output redirection
        cmd = f'cmd.exe /c {command} > {output_path} 2>&1'
        self.processClass.Create(cmd, NULL, NULL)
        
        # Wait for execution
        time.sleep(2)
        
        # Read output using TYPE command
        read_cmd = f'cmd.exe /c type {output_path}'
        # Note: Would need SMB connection to actually retrieve the file
        # This is a simplified example
        
        # Clean up
        del_cmd = f'cmd.exe /c del {output_path}'
        self.processClass.Create(del_cmd, NULL, NULL)
        
    def __del__(self):
        self.dcom.disconnect()

# Usage
shell = WMIShell('192.168.1.100', 'admin', 'pass')
shell.execute('whoami')
shell.execute('ipconfig')

​
Event Subscriptions (Persistence)

from impacket.dcerpc.v5.dcomrt import DCOMConnection
from impacket.dcerpc.v5.dcom import wmi
from impacket.dcerpc.v5.dtypes import NULL

dcom = DCOMConnection('192.168.1.100', 'user', 'pass', 'DOMAIN')

try:
    iInterface = dcom.CoCreateInstanceEx(wmi.CLSID_WbemLevel1Login, wmi.IID_IWbemLevel1Login)
    iWbemLevel1Login = wmi.IWbemLevel1Login(iInterface)
    iWbemServices = iWbemLevel1Login.NTLMLogin('//./root/subscription', NULL, NULL)
    
    # Create event filter (trigger)
    filterClass, _ = iWbemServices.GetObject('__EventFilter')
    filterInstance = filterClass.SpawnInstance()
    filterInstance.Name = 'MyEventFilter'
    filterInstance.EventNamespace = 'root/cimv2'
    filterInstance.QueryLanguage = 'WQL'
    filterInstance.Query = 'SELECT * FROM __InstanceCreationEvent WITHIN 5 WHERE TargetInstance ISA "Win32_Process"'
    
    iWbemServices.PutInstance(filterInstance.marshalMe())
    
    # Create event consumer (action)
    consumerClass, _ = iWbemServices.GetObject('CommandLineEventConsumer')
    consumerInstance = consumerClass.SpawnInstance()
    consumerInstance.Name = 'MyConsumer'
    consumerInstance.CommandLineTemplate = 'cmd.exe /c calc.exe'
    
    iWbemServices.PutInstance(consumerInstance.marshalMe())
    
    # Bind filter to consumer
    bindingClass, _ = iWbemServices.GetObject('__FilterToConsumerBinding')
    bindingInstance = bindingClass.SpawnInstance()
    bindingInstance.Filter = filterInstance.getObjectText(0)
    bindingInstance.Consumer = consumerInstance.getObjectText(0)
    
    iWbemServices.PutInstance(bindingInstance.marshalMe())
    
    print("WMI event subscription created for persistence")
    
finally:
    dcom.disconnect()

​
DCOM Direct Interface Access

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ShellWindows Interface

from impacket.dcerpc.v5.dcomrt import DCOMConnection
from impacket.dcerpc.v5.dcom.oaut import IID_IDispatch, IDispatch, DISPPARAMS, DISPATCH_PROPERTYGET, VARIANT, DISPATCH_METHOD

# ShellWindows CLSID
CLSID_ShellWindows = '{9BA05972-F6A8-11CF-A442-00A0C90A8F39}'
IID_ShellWindows = '{85CB6900-4D95-11CF-960C-0080C7F4EE85}'

dcom = DCOMConnection('192.168.1.100', 'user', 'pass')

try:
    # Create ShellWindows instance
    iInterface = dcom.CoCreateInstanceEx(CLSID_ShellWindows, IID_IDispatch)
    iDispatch = IDispatch(iInterface)
    
    # Get Item method
    dispParams = DISPPARAMS()
    dispParams['rgvarg'] = NULL
    dispParams['cArgs'] = 0
    
    # Call methods through IDispatch
    resp = iDispatch.Invoke(0x60020002, 0, DISPATCH_PROPERTYGET, dispParams)
    
finally:
    dcom.disconnect()

​
MMC20.Application

from impacket.dcerpc.v5.dcomrt import DCOMConnection
from impacket.dcerpc.v5.dcom.oaut import IID_IDispatch, IDispatch

CLSID_MMC20 = '{49B2791A-B1AE-4C90-9B8E-E860BA07F889}'

dcom = DCOMConnection('192.168.1.100', 'user', 'pass')

try:
    iInterface = dcom.CoCreateInstanceEx(CLSID_MMC20, IID_IDispatch)
    iMMC = IDispatch(iInterface)
    
    # Execute commands through MMC Document.ActiveView.ExecuteShellCommand
    # This requires more complex IDispatch calls
    
finally:
    dcom.disconnect()

​
Authentication Options

# Username/password
dcom = DCOMConnection('192.168.1.100', 'user', 'pass', 'DOMAIN')

# Kerberos
import os
os.environ['KRB5CCNAME'] = '/tmp/krb5cc_1000'
dcom = DCOMConnection(
    '192.168.1.100',
    'user',
    'pass',
    'DOMAIN',
    oxidResolver=True,
    doKerberos=True,
    kdcHost='dc.domain.local'
)

# NTLM hash
dcom = DCOMConnection(
    '192.168.1.100',
    'user',
    '',
    'DOMAIN',
    lmhash='',
    nthash='aad3b435b51404eeaad3b435b51404ee'
)

​
Error Handling

from impacket.dcerpc.v5.dcom.wmi import DCERPCSessionError
from impacket.dcerpc.v5.rpcrt import DCERPCException

try:
    dcom = DCOMConnection('192.168.1.100', 'user', 'wrongpass')
except DCERPCSessionError as e:
    print(f"Authentication failed: {e}")
except DCERPCException as e:
    print(f"DCOM error: {e}")
except Exception as e:
    print(f"Connection error: {e}")

​
DCOM Port Requirements

  • TCP 135: RPC Endpoint Mapper
  • TCP 49152-65535: Dynamic RPC ports (Windows 2008+)
  • TCP 1024-5000: Dynamic RPC ports (older Windows)
To restrict DCOM to specific ports, configure the server’s RPC settings.

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Security Considerations

  1. Authentication: DCOM requires valid credentials
  2. Privileges: WMI access requires local admin rights
  3. Firewall: DCOM uses dynamic ports that may be blocked
  4. Logging: WMI activity is logged in Windows Event Logs
  5. Detection: WMI process creation is commonly monitored by EDR

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Best Practices

  1. Always disconnect DCOM connections properly
  2. Handle exceptions for network and authentication errors
  3. Use specific WQL queries instead of SELECT * for performance
  4. Clean up WMI event subscriptions after use
  5. Consider using RemRelease() for interface cleanup

​
References

  • [MS-DCOM]: Distributed Component Object Model (DCOM) Remote Protocol
  • [MS-WMI]: Windows Management Instrumentation Remote Protocol
  • [MS-WMIO]: Windows Management Instrumentation Encoding
  • WQL (WMI Query Language) Documentation

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