Processus Windows

Un lien très interressant qui fait la synthese des processus de base de windows:

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

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

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 SYSTEM\CurrentControlSet\Services
%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
I have not personally seen malware try and impersonate LSM.exe, but there is always a first so keep your eyes open.
%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.

Let’s sum this post up by creating a simple checklist to review while looking for malicious/suspect process activity.

Check the parent/child relationships of processes.
Check which users names the processes are running under
Check their command line parameters for those processes that use them.
Check their digital signatures
Check their base priorities
Check the location they are being from
Check their spellings
Leverage memory analysis to detect hidden and/or injected process. Some malware can hide processes by unlinking them (among other ways). Memory analysis is a must these days.
When you get comfortable with everything here, dig deeper and check what modules are typically loaded for each process.
Check and see if processes that should not be connecting out to the internet are not
Check process privileges
If wscript.exe process is running check the command line of what it is running.
Investigate processes running inside %temp%, root of %appdata%, %localappdata%, recycle bin, etc.
If rundll32.exe is running check its command line as well.
“Most” legitimate user applications like Adobe, Web browsers, etc. don’t spawn child processes like cmd.exe. If you see this, they should be investigated.
Core Windows processes shouldn’t be communicating out to the internet. If you see communication from these processes, dig deeper. Look for suspicious URLs/IPs, check process strings, etc.