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Binary Exploitation
Binary Blueprint

Binary Blueprint

🔍 Details

AttributeDetails
Challenge NameBinary Blueprint
CategoryBinary Exploitation
Difficulty🟠 Medium
FlagF4H{8ba0cfe5c7**********}

📝 Description

You are given an executable binary—your task is to determine how many external shared libraries it depends on.

After retrieving the number of external libraries, run the command from file flag_generator.txt in the terminal, replacing X (currently 42) with the number you obtained. Result will be the flag.

⚠️

DO NOT TRY BRUTEFORCING, YOU HAVE ONLY 3 ATTEMPTS!


📥 Download gpg_binary

📥 Download flag_generator.txt

🧩 Hints

  1. Understanding dependencies is a key step in reverse engineering. Every dynamically linked binary relies on shared libraries to function.
  2. Try using tools that reveal dynamic linking information — what might show "NEEDED" entries in an ELF binary?

💡 Solution

  1. Use objdump to inspect the binary: 
    objdump -p gpg_binary | grep NEEDED | wc -l
  2. This command counts how many NEEDED entries (shared libraries) the binary requires.
  3. After retrieving the number of external libraries, run the command from file flag_generator.txt in the terminal, replacing X (currently 42) with the number you obtained.
  4. Vuala! You have the flag.

📚 Insights

  • Identifying a binary’s shared library dependencies helps you understand its behavior and potential weak points. Tools like objdump -p, readelf -d, or ldd are commonly used.
  • If a binary depends on libc.so.6, you might be able to exploit exposed functions like system() or execve().
  • Techniques like LD_PRELOAD can override functions in dynamically linked binaries, enabling privilege escalation or data exfiltration.
  • Understanding dependencies is crucial in CTF exploitation and real-world scenarios where vulnerable libraries are in use.
  • For example, GnuPG 1.4.19 had a serious vulnerability:

🤔 Comments

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