Windows Core Processes

There are two broad categories of Windows core processes. Processes that initialize system environment and those that initialize the user environment. Whatever is the category, you need to know them well in order to detect abnormal things.

Boot

BIOS, POST, Boo Loader (NLTDR), Kernl (NTOSKERNEL), files: win.sys, HAL.DLL, system.ini, sizedit.exe, config.exe, autoexec.BAT, MISCONFIG.exe.

Main Processes

Below is the overview of the main processes in Windows. There are several core process that are important to examine since malware often drool 🤤 over them. Singleton - one instance running only. One instance lsass, services, System, winint, lsm.exe ❓. If any of these having more than 1 process should be the object of further investigation.

The process tree

• IDLE
• System (PID 4).
  • Memory Compression
  • smss.exe
• csrss
• wininit
  • services
  • lsass
• winlogon
  • logonUI. Terminates once complete
  • userinit. Terminates once complete
    • explorer

IDLE or System Idle Process

Parent 🤱: None.

Children 👧 : None

Singleton ☝️:

Path to file 🛣: None

Account: Local System

Start time: Boot

The first and the most importnat process that “gives birth” to other processes - IDLE. 🔍 It doesn’t have an image file on disk, so if you see IDLE.exe, it is most likely a malware 🦠 (or you have been sophisticatedly pranked 😉). PID is usually 0.

🔎 Are IDLE and System Idle Process the same thing?

🧪 If I dump a process that doesn’t have an image file, will it still have a PE header?

Runs in system memory space.

System

Parent 🤱: None.

Children 👧 : smss, Interrupts, Memory Compression

Singleton ☝️: Yes

Path to file 🛣: None

Account: Local System

Start time: Boot

Handles kernel mode system threads, different device drivers, waiting for I/O etc. PID is usually 4.

Runs in system memory space.

Memory Compression

Parent 🤱: System

Children 👧 : None

Singleton ☝️:

Path to file 🛣: None

Account: Local System

Start time: Boot

Compresses the memory of the user space. Doesn’t have an image file on disk. Not really interesting for DFIR.

smss

Parent 🤱: System

Children 👧 : None

Singleton ☝️: No

Path to file 🛣: System32

Account: Local System

Start time: Boot

Session manager process. The first user-mode process. Run from System32 directory. There are two instances:

• master instance perfroms some init stuff. Reads and writes to registry preparing the OS for use. Initializes the registry hives
• session startup instance. Creates three subsystem processes and exits: csrss.exe,

winlogon

Parent 🤱: None.

Children 👧 : None

Singleton ☝️: No

Path to file 🛣: System32

Account: Local System

Start time: varies

Another process of particilar interest is msc.

wininit

Parent 🤱: None.

Children 👧 : lsm, lsass, services

Singleton ☝️: Yes

Path to file 🛣: System32

Account: Local System

Start time: Boot

lsass

Parent 🤱: wininit

Children 👧 : None

Singleton ☝️: Yes

Path to file 🛣: System32

Account: Local System

Start time: Boot

lsass. This is the main process of Windows OS that’s responsible for authentication and authorisation. More about lsass here.

svchost

Parent 🤱: services

Children 👧 : Lots of:

Singleton ☝️: No

Path to file 🛣: System32

Account: Local System, Network Service, Local Service

Start time: Boot

🦠 This one is very ofter used by malware for disguise. It has lot’s of instances.

csrss

Parent 🤱: none

Children 👧 :

Singleton ☝️: No

Path to file 🛣: System32

Account: Local System

Start time: Boot

taskhost

Parent 🤱: services

Children 👧 : Lots of:

Singleton ☝️: No

Path to file 🛣: System32

Account: many

Start time: varies

lsaiso

Parent 🤱: winint.exe

Children 👧 : None

Singleton ☝️: Yes

Path to file 🛣: None

Account: Local System

Start time: Boot

Windows Credential Guard. Only for Windows 10 Enterprise or Windows Server 2016 and above. Also, this exe is present on a Windows 11 system, but is not running. It’s a singleton and is located on disk in System32 directory. It runs under local system account and it’s parent is winint.exe. Works in the isolated user mode, so that even the kernel doesn’t have access to it. Secure Kernel protected by Hyper-V is talking to lsaiso instead. Kernel Mode and Secure Kernel are talking using a small buffer. VSL calls. Between SK and lsaiso - sys call. VSM container: lsaiso, credentials, secure kernel, kernel mode code integrity. HVCI - Hyper-V code integrity.

mimikatz.exe
> version
privilege::debug
securlsa::logonpasswords

> misc::memssp

userinit

Parent 🤱: winlogon

Children 👧 : explore

Singleton ☝️:

Path to file 🛣:

Account:

Start time:

explorer

Parent 🤱: userinit. Since the parent terminates once it’s done everything, explorer won’t have a parent in process tree.

Children 👧 : iexplore

Singleton ☝️: No

Path to file 🛣: %Systemroot%\

Account: Local Users

Start time: varies

iexplore

Parent 🤱: explorer

Children 👧 : None

Singleton ☝️: Yes

Path to file 🛣: Program Files\Internet Explorer\iexplore.exe

Account: Local Users

Start time: Boot

lsm

Parent 🤱: wininit

Children 👧 : None

Singleton ☝️: Yes

Path to file 🛣: System32

Account: Local System

Start time: Boot

services

Parent 🤱: wininit

Children 👧 : svchost, taskhost

Singleton ☝️: Yes

Path to file 🛣: System32

Account: Local System

Start time: Boot

Quick Check List

Singletons vs Cloners

Singletons: System, wininit, lsass.exe, lsm.exe, lsaiso, services.exe

Cloners: sms, taskhost, winlogon, iexplore, explorer, svchost, csrss

grep -E -i "(system|wininit|lsass|lsm|services)" "psscan.txt|pslist.txt" > singletons.txt

Boot vs Varies

Boot: System, sms, wininit, lsass, lsm, svchost*, services, csrss

Varies: taskhost, winlogon, iexplore, explorer, svchost*

grep -E -i "(system|wininit|lsass|lsm|services|sms|csrss)" "psscan.txt|pslist.txt" > boottime.txt

grep -E -i -v <2019-01-20> psscan.txt > nonboot.txt

System32 vs Other

System32: System, sms, wininit, taskhost, lsass, winlogon, lsm, svchost, services, csrss, lsaiso

Other: iexplore, explorer

WinCore vs Other

Non Wincore:

grep -E -i -v "(system|wininit|lsass|lsm|services|sms|taskhost|winlogon|iexplore|explorer|svchost|csrss)" "psscan.txt|pslist.txt" > all_non_core.txt

WinCore:

grep -E -i "(system|wininit|lsass|lsm|services|sms|taskhost|winlogon|iexplore|explorer|svchost|csrss)" "psscan.txt|pslist.txt" > all_non_core.txt

References

[1] SDF Podcast, by Michael Leclair