blackjack - pwnable

题目

题目要求我们在21点游戏中，赢得100万，就可以获得flag。也给出源码

源码分析

连上服务器玩了几盘之后发现，赢是可以赢的，也可以写脚本自动运行，但是赚钱速度太慢。题目提示我们去看看源码，一番查看之后我们发现这个重点：

//Global Variables
int bet;int betting() //Asks user amount to bet
{printf("\n\nEnter Bet: $");scanf("%d", &bet);if (bet > cash) //If player tries to bet more money than player has{printf("\nYou cannot bet more money than you have.");printf("\nEnter Bet: ");scanf("%d", &bet);return bet;}else return bet;
} // End Function

bet定义的是数值类型；判断下注金额与拥有的现金，仅仅通过bet>cash的简单判断语句。忽略了当bet为负数的情况。

我们尝试一下输入负赌注：

Cash: $500
-------
|D    |
|  9  |
|    D|
-------Your Total is 9The Dealer Has a Total of 10Enter Bet: $-999999999Would You Like to Hit or Stay?
Please Enter H to Hit or S to Stay.
sYou Have Chosen to Stay at 9. Wise Decision!The Dealer Has a Total of 12
The Dealer Has a Total of 14
The Dealer Has a Total of 16
The Dealer Has a Total of 18
Dealer Has the Better Hand. You Lose.You have 0 Wins and 1 Losses. Awesome!Would You Like To Play Again?
Please Enter Y for Yes or N for No
yYaY_I_AM_A_MILLIONARE_LOL //flagCash: $1000000499
-------
|H    |
|  4  |
|    H|
-------Your Total is 4The Dealer Has a Total of 4Enter Bet: $

flag再进行新一轮游戏的时候出来了。

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blackjack - pwnable

blackjack - pwnable

题目

源码分析

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