[MRCTF2020]Ezaudit

知識點

1.原始碼洩露

2.偽隨機數

3.sql注入？

題解

開啟題目是個漂亮的前端，掃一下發現www.zip檔案洩露，下載審計

<?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 == '')) {
        // 若為空,視為未填寫,提示錯誤,並3秒後返回登入介面
        header('refresh:2; url=login.html');
        echo "使用者名稱、密碼、金鑰不能為空啦,crispr會讓你在2秒後跳轉到登入介面的!";
        exit;
}
    else if($Private_key != '*************' )
    {
        header('refresh:2; url=login.html');
        echo "假金鑰，咋會讓你登入?crispr會讓你在2秒後跳轉到登入介面的!";
        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???
 

根據最後一行提示，我們需要通過公鑰找到私鑰，這裡使用了mt_rand()函式，具體可以看一下連結文章講的很詳細。

爆破seed

str1='abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789'
str2='KVQP0LdJKRaV3n9D'
str3 = str1[::-1]
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)
 

用php_mt_seed算出種子為1775196155

算出私鑰

<?php
mt_srand(1775196155);
//公鑰
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 $public_key;
}
//私鑰
function private_key($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();
echo private_key();
?>
 

index.php中有一個login.html直接訪問，輸入賬號密碼私鑰登入得到flag（萬能密碼）

end