Write UP kksi RE "kakaesi" ヽ(ﾟДﾟ)ﾉ (day 45)

Ok lanjut lagi nih dapat soal KKSI dari senior buat dicobain kali ini menarik karena dikasih binari windows 64 bit

Mari kita kerjakan sama-sama. Pertama-tama jalankan binarinya di windows agar kita tahu cara kerja dari programnya.

oke cukup simpel cara kerjanya kita diminta untuk memasukan string dan program akan tertutup jika itu salah. Kita coba analisa string dari binarinya dulu mungkin ada petunjuk tentang flagnya.

saat diliat stringnya tidak ada petunjuk tentang flag tetapi bisa dilihat program ini mencoba memanggil library python27.dll dan banyak string yang mengindikasikan nama dari sebuah program python seperti .pyd, .pyz .

oke jadi saya pikir ini merupakan program python yang sudah di compile menjadi .exe dengan memakai tools pyinstaller (link:https://pypi.org/project/PyInstaller/)

agar kita bisa mendapatkan source code asli dari .exe ini kita perlu pakai dua tools ini yaitu https://sourceforge.net/projects/pyinstallerextractor/ agar bisa menngubah .exe -> .pyc dan https://sourceforge.net/projects/easypythondecompiler/ untuk mengubah .pyc -> .py

jalankan program pyinstxtractor seperti diatas untuk melakukan proses ekstraksi dari program .exe dan hasilnya akan ada satu direktori yang mempunyai prefix "_extracted" diujung nya

masuk kedalam direktori tersebut dan bisa dilihat ada beberapa program dan library python didalamnya.

source code .pyc yang sebenarnya ada di file bernama "kakaesi" tetapi masalahnya saat kita buka masih dalam bentuk binari agar bisa mengembalikan ke source code awal pertama-tama kita harus membetulkan header file dengan menambahkan "magic number" di awal file seperti dibawah.

ambil saja 7 bytes pertama dari program librarynya (dalam contoh ini saya pakai library __future__.pyc boleh pilih python mana saja asalkan ujungnya .pyc) dari binarinya yaitu (03 3F 0D 0A 00 00 00 00) lalu tambahkan di awal file "kakaesi" dan jangan lupa terakhir ubah ektensi file menjadi .pyc

setelah membetulkan file nya tinggal dimasukan ke tools easy python decompiler dan nanti akan mengeluarkan file bernama "kakaesi.pyc_dis"

selesai dan kita tinggal buka source code nya dengan text editor favorit kalian seperti dibawah ini.

Kalau dilihat sekilas menurut saya cukup jelas kalau programnya meminta tiga data untuk autentikasi yaitu username, password dan kode dan juga semuanya bisa kita dapatkan di source code

yes kita dapat flagnya !

enjoy :)

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