Standard Windows processes: a brief reference

Useful in forensics analysis and incident response

During the analysis phase, after (for example) a system compromization, is very important to know the standard Windows processes, in order to have a ‘baseline’ useful to make a ‘diff’ with the compromised system.

On this article, Patrick Olsen has developed a simple list of base processes, focused on Windows 7:

Idle and System

  • Created by ntoskrnl.exe via the process manager function, which creates and terminates processes and threads.
  • No visible parent processes
  • System has a static PID of 4
  • System creates smss.exe
  • There should only be one system process running

SMSS — Session Manager

  • First user mode process
  • Parent process is System
  • Base Priority of 11
  • Username: NT AUTHORITY\SYSTEM
  • Performs delayed file delete/rename changes
  • Loads known dlls
  • Runs from \%systemroot%\System32\smss.exe
  • Creates session 0 (OS services)
  • Creates session 1 (User session)
  • Creates csrss and winlogon then exits, which is why they have no parent process and they both have session ids of 1
  • Runs within session 0
  • Only one smss.exe process should be running at one time. The second smss.exe process exits, so you will only see the one running in session 0.
  • There can be more sessions if more users are logged on to the system. 0 and 1 are for a single user logged onto the system.

CSRSS.EXE — Client/Server Run

  • Windows subsystem process.
  • Base Priority of 13
  • \%SystemRoot%\system32\csrss.exe
  • Username: NT AUTHORITY\SYSTEM
  • Creates/Deletes processes and threads, Temp files, etc.
  • In XP its used to draw text based console windows. Under Windows 7, the conhost process now does that functionality. For example, cmd.exe
  • One csrss process per session
  • Its name is often used by malware to hide on systems (CSSRS.EXE, CSRSSS.EXE, etc.)
  • Runs within session 0

WININIT.EXE — Windows Initialization Process

  • Parent to services.exe (SCM), lsass.exe and lsm.exe
  • Created by smss.exe, but since smss.exe exits there is no parent to WININIT.
  • Base Priority of 13
  • Username: NT AUTHORITY\SYSTEM
  • \%SystemRoot%\system32\wininit.exe
  • Performs user-mode initialization tasks
  • Creates \%windir%\temp
  • Runs within session 0

SERVICES.EXE — Service Control Manager

  • Child to WININIT.EXE
  • Parent to services such at svchost.exe, dllhost.exe, taskhost.exe, spoolsv.exe, etc. Services are defined in SYSTEMCurrentControlSetServices
  • \%SystemRoot%\System32\wininit.exe
  • Username: NT AUTHORITY\SYSTEM
  • Base Priority of 9
  • Loads a database of services into memory
  • Runs within session 0
  • There should only be one services.exe process running

LSASS.EXE — Local Security Authority

  • Child to WININIT.EXE
  • Only one lsass.exe process
  • %SystemRoot%\System32\lsass.exe
  • Responsible for local security policy to include managing users allowed to login, password policies, writing to the security event log, etc.
  • Often targeted by malware as a means to dump passwords. Also mimicked by malware to hide on a system (lass.exe, lssass.exe, lsasss.exe, etc.). These “fake” names will not be a children of wininit.exe.
  • Base Priority of 9
  • Username: NT AUTHORITY\SYSTEM
  • Runs within session 0
  • It should not have child processes

SVCHOST.EXE — Service Hosting Process

  • Multiple instances of svchost.exe can/do exist/run
  • %SystemRoot%\System32\svchost.exe
  • Username: Should only be one of three options: NT AUTHORITY\SYSTEM, LOCAL SERVICE, or NETWORK SERVICE
  • Should always have a parent of services.exe
  • Base Priority of 8
  • Often mimicked (scvhost, svch0st, etc.) When they are mimicked they will not be running as children to services.exe.
  • Command Line: svchost.exe -k <name>
  • -k <name> values should exist within the Software\Microsoft\Windows NT\CurrentVersion\Svchost registry key
  • Often times when malware uses the actual svchost.exe to load their malicious service they will not include -k command line parameters and be running under a username that does not match on of the three listed in bullet 3.
  • They should all be running within session 0

LSM.EXE — Load Session Manager Service

  • Manages the state of terminal server sessions on the local machine. Sends the requests to smss.exe to start new sessions.
  • Child to wininit.exe
  • It should not have child processes
  • Receives logon/off, shell start and termination, connect/disconnects from a session, and lock/unlock desktop
  • %systemroot%\System32\lsm.exe
  • Base Priority of 8
  • Username: NT AUTHORITY\SYSTEM
  • Runs within session 0

WINLOGON.EXE — Windows Logon Process

  • No parent process
  • Could have a child process of LogonUI if smartcard, etc. are used to authenticate
  • LogonUI will terminate once the user enters their password. Once password is entered the verification is sent over to LSASS and it’s verified via Active Directory or SAM (the registry hive SAM), which stores local users and group information.
  • Base Priority of 13
  • Runs within session one
  • Handles interactive user logons/logoffs when SAS keystroke combination is entered (Ctrl+Alt+Delete)
  • Loads Userinit within Software\Microsoft\Windows NT\CurrentVersion\Winlogon
  • The userinit value in the registry should be: Userinit.exe, (note the comma). Malware will sometimes add additional values to this key, which will load malware upon successful logons.
  • Userinit.exe exits once it runs so you wont see this process running when you look.
  • Userinit initializes the user environment. This includes running GPOs and logon scripts.
  • Will run Shell value located at Software\Microsoft\Windows NT\CurrentVersion\Winlogon within the registry. The value of shell should be Explorer.exe. Malware will also use this sometimes to execute malware by adding values.
  • Since Userinit exists this is also why Explorer.exe doesn’t have a parent process.

Explorer.exe — AKA Windows Explorer

  • No parent process since Userinit.exe exits
  • The value “Explorer.exe” is stored in shell value within the registry. The registry location is here: Software\Microsoft\Windows NT\CurrentVersion\Winlogon\Shell
  • Base Priority of 8
  • Username: The logged on user account.
  • %Systemroot%\Explorer.exe
  • This will contain multiple child processes.
  • Some of you might know this better as, “Windows Explorer”
  • This process is often targeted by malware. Malware will often times inject this process. One indication of this is if Explorer.exe is connecting out to the internet. There are other indicators, but that’s another post. We are keeping it simple here.

Great, but Windows 10?

However, this (great!) list needs some upgrades after the release of Windows 10.
So, you can find some useful information on this post on forensicsfocus.com:

Some highlights:

  • System still has the PID 4 and is the parent of the Windows Session Manager. I will also mention that it still resides at %systemroot%system32.
  • All services are started from executable files from their former locations
  • There are still two Client Server Runtime Processes (csrss.exe), one of which has the same parent as wininit.exe from an ended smss.exe process.
  • The super-process winit.exe spawns services.exe, lsass.exe and the invisible lsm.exe process to start the Local Session Manager. Starting from Windows 8, lsm.exe is started inside a Service Host process from svchost.exe from the command line %systemrootsystem32svchost.exe -k DcomLaunch.
  • The WinLogon Service, which is responsible for Interactive Logons on a Windows Operating System, remains where it has always been for Session 1 and is started for every interactive user session.
  • Microsoft has renamed the Host Process for Windows Tasks again. In Windows 7 it was named taskhost.exe, in Windows 8 it was called taskhostex.exe and the new name is taskhostw.exe in Windows 10.
    The primary purpose, serving as a generic “Host Process”, remains unchanged, as does the location in %systemroot%\system32.
  • The Console Windows Host conhost.exe has been running as a child of cmd.exe since Windows 8, and not as a child of csrss.exe as it was in Windows 7. The executable file for Pathping is a child of cmd.exe in the same way conhost.exe is. There is no longer any separation of conhost.exe under the user’s own Client Server Runtime Service csrss.exe and the cmd.exe process under explorer.exe.

The new Microsoft Edge web browser, the successor of Internet Explorer. Microsoft Edge starts four processes:

  • Two processes named MicrosoftEdgeCP.exe, started from C:WindowsSystemApps.. with the permission of the current user. Microsoft Edge starts with two of them for the first visible tab inside the browser window. Both are child processes of RuntimeBroker.exe, which is a child of svchost.exe, the Host Process for Windows Services. Runtime Broker starts automatically with the Operating System.
  • A new MicrosoftEdge process is started under the Runtime Broker Service for every new tab that is opened by the browser. Microsoft is also introducing the new path %systemroot%\SystemApps and starting a web browser as a sub-child of svchost.exe, which breaks traditions in the process design.
  • Directly spawned from svchost.exe is the process MicrosoftEdge.exe (without “CP” at the end of the file name). This is the main browser application process. And again, the executable file is saved in a subfolder of C:\Windows\SystemApps.
  • The Host Process svchost.exe starts a fourth executable file called browser_broker.exe.
    This time Microsoft is following its own design traditions and has stored the file in the well-known path %systemroot%\system32.

References

http://sysforensics.org/2014/01/know-your-windows-processes/

 

http://sysforensics.org/2014/01/know-your-windows-processes/

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