Shop (Reverse Engineering)
Best Stuff - Cheap Stuff, Buy Buy Buy... Store Instance: source. The shop is open for business at nc mercury.picoctf.net 10337.
添付ファイル
・source
とりあえず実行する。
$ nc mercury.picoctf.net 10337
Welcome to the market!
=====================
You have 40 coins
Item Price Count
(0) Quiet Quiches 10 12
(1) Average Apple 15 8
(2) Fruitful Flag 100 1
(3) Sell an Item
(4) Exit
Choose an option:
0
How many do you want to buy?
-128
You have 1320 coins
Item Price Count
(0) Quiet Quiches 10 140
(1) Average Apple 15 8
(2) Fruitful Flag 100 1
(3) Sell an Item
(4) Exit
Choose an option:
2
How many do you want to buy?
1
Flag is: [112 105 99 111 67 84 70 123 98 52 100 95 98 114 111 103 114 97 109 109 101 114 95 51 100 97 51 52 97 56 102 125]
1バイトの負の境界を狙った。
112 105 99 111 67 84 70 123 98 52 100 95 98 114 111 103 114 97 109 109 101 114 95 51 100 97 51 52 97 56 102 125をcyberchefでfrom decimalする。
フラグが得られた。
picoCTF{b4d_brogrammer_3da34a8f}