进入主页，没发现有什么明显的漏洞

查看一下源代码，也没有什么发现

猜测有备份文件

dirmap扫描一下

发现有www.zip

<?php 
header('Content-type:text/html; charset=utf-8');
error_reporting(0);
if(isset($_POST['login'])){
    $username = $_POST['username'];
    $password = $_POST['password'];
    $Private_key = $_POST['Private_key'];
    if (($username == '') || ($password == '') ||($Private_key == '')) {
        // 若为空,视为未填写,提示错误,并3秒后返回登录界面
        header('refresh:2; url=login.html');
        echo "用户名、密码、密钥不能为空啦,crispr会让你在2秒后跳转到登录界面的!";
        exit;
}
    else if($Private_key != '*************' )
    {
        header('refresh:2; url=login.html');
        echo "假密钥，咋会让你登录?crispr会让你在2秒后跳转到登录界面的!";
        exit;
    }

    else{
        if($Private_key === '************'){
        $getuser = "SELECT flag FROM user WHERE username= 'crispr' AND password = '$password'".';'; 
        $link=mysql_connect("localhost","root","root");
        mysql_select_db("test",$link);
        $result = mysql_query($getuser);
        while($row=mysql_fetch_assoc($result)){
            echo "<tr><td>".$row["username"]."</td><td>".$row["flag"]."</td><td>";
        }
    }
    }

} 
// genarate public_key 
function public_key($length = 16) {
    $strings1 = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';
    $public_key = '';
    for ( $i = 0; $i < $length; $i++ )
    $public_key .= substr($strings1, mt_rand(0, strlen($strings1) - 1), 1);
    return $public_key;
  }

  //genarate private_key
  function private_key($length = 12) {
    $strings2 = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';
    $private_key = '';
    for ( $i = 0; $i < $length; $i++ )
    $private_key .= substr($strings2, mt_rand(0, strlen($strings2) - 1), 1);
    return $private_key;
  }
  $Public_key = public_key();
  //$Public_key = KVQP0LdJKRaV3n9D  how to get crispr's private_key???

可以看到已经给出了公钥，需要去求私钥

查了一下mt_read这个函数

真的是随机数的话私钥就算不出来了。。

在查了下发现这个函数有个伪随机数漏洞

可以来测试一下

<?php

mt_srand(2131321);
echo "当rand值为2131321时生成的伪随机数列：\n";
for($i = 0; $i < 5 ;$i++){
    echo mt_rand()."\n";
}

mt_srand(111521521);
echo "当rand值为111521521时生成的伪随机数列:\n";
for($k=0 ;$k < 5; $k++){
    echo mt_rand()."\n";
}

mt_srand(111);
echo "当rand值为111时生成的伪随机数列:\n";
for($k=0 ;$k < 5; $k++){
    echo mt_rand()."\n";
}
?>

<?php

mt_srand(111);
echo "当rand值为111时生成的伪随机数列：\n";
for($i = 0; $i < 5 ;$i++){
    echo mt_rand()."\n";
}
?>

 所以当拿到seed时就可以算出私钥了

下载一下php_mt_seed工具来爆破seed

先将公钥转换成脚本能识别的数列

str1='abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789'
str2='KVQP0LdJKRaV3n9D'
length = len(str2)
res=''
for i in range(len(str2)):
    for j in range(len(str1)):
        if str2[i] == str1[j]:
            res+=str(j)+' '+str(j)+' '+'0'+' '+str(len(str1)-1)+' '
            break
print(res)

知道了seed也知道了php版本

<?php
mt_srand(1775196155);
function public_key($length = 16) {
    $strings1 = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';
    $public_key = '';
    for ( $i = 0; $i < $length; $i++ )
    $public_key .= substr($strings1, mt_rand(0, strlen($strings1) - 1), 1);
    return $public_key;
  }
 
  //genarate private_key
function private_key($length = 12) {
    $strings2 = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';
    $private_key = '';
    for ( $i = 0; $i < $length; $i++ )
    $private_key .= substr($strings2, mt_rand(0, strlen($strings2) - 1), 1);
    return $private_key;
  }
echo public_key() . "<br>";
echo private_key();
 
?>

 得到了私钥

 得到了flag

参考文章：https://blog.csdn.net/czc1997/article/details/78167705