什么是二次注入
二次注入可以理解为,攻击者构造的恶意数据存储在数据库后,恶意数据被读取并进入到SQL查询语句所导致的注入。防御者可能在用户 输入恶意数据时对其中的特殊字符进行了转义处理,但在恶意数据插入到数据库时被处理的数据又被还原并存储在数据库中,当web程序调用存储在数据库中的恶意数据并执行SQL查询时,就发生了sql二次注入。
二次注入原理分为两步
二次注入,可以概括为以下两步:
第一步:插入恶意数据
进行数据库插入数据时,对其中的特殊字符进行了转义处理,在写入数据库的时候又保留了原来的数据。
第二步:引用恶意数据
开发者默认存入数据库的数据都是安全的,在进行查询的时候,直接从数据库中取出恶意数据,没有进行进一步的检验的处理。
二次注入的过程
找到注入点
然后构造注入语句
以sql-lab第24关为例:
username:abcd’#(单引号来闭合前面的单引号,#注释后面内容)
password:1234
username:abcd’#
password:1234
登录后出现如下效果:you are logged in
查看一下
后台代码
new_user.PHP
<?PHP
include '../sql-connections/sql-connect.PHP' ;
?>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" >
<html>
<head>
<Meta http-equiv="content-type" content="text/html; charset=ISO-8859-1">
<title><?PHP echo $Feedback_title_ns; ?> </title>
</head>
<body bgcolor="#000000">
<div align="right">
<a style="font-size:.8em;color:#FFFF00" href='index.PHP'><img src="../images/Home.png" height='45'; width='45'></br>HOME</a>
</div>
<font size="3" color="#FFFF00">
<div style="text-align:center">
<form name="mylogin" method="POST" action="login_create.PHP">
<h2 style="text-align:center;background-image:url('../images/Less-24-new-user.jpg');background-repeat:no-repeat;background-position:center center">
<div style="padding-top:300px;text-align:center;color:#FFFF00;"><?PHP echo $form_title_ns; ?></div>
</h2>
<div align="center">
<table style="margin-top:50px;">
<tr>
<td style="text-align:right">
<font size="3" color="#FFFF00">
<strong>Desired Username:</strong></font>
</td>
<td style="text-align:left">
<input name="username" id="username" type="text" value="" />
</td>
</tr>
<tr>
<td style="text-align:right">
<font size="3" color="#FFFF00">
<strong>Password:</strong>
</font>
</td>
<td style="text-align:left">
<input name="password" id="password" type="password" value="" />
</td>
</tr>
<tr>
<td style="text-align:right">
<font size="3" color="#FFFF00">
<strong>Retype Password:</strong>
</font>
</td>
<td style="text-align:left">
<input name="re_password" id="re_password" type="password" value="" />
</td>
</tr>
<tr>
<td colspan="2" style="text-align:right">
<input name="submit" id="submit" type="submit" value="Register" /><br/><br/>
</td>
</tr>
</table>
</div>
</form>
</div>
</body>
</html>
index.PHP
<?PHP
session_start();
if (isset($_SESSION['username']) && isset($_COOKIE['Auth'])) {
header('Location: logged-in.PHP');
}
?>
<?PHP
//including the MysqL connect parameters.
include("../sql-connections/sql-connect.PHP");
?>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" >
<html>
<head>
<Meta http-equiv="content-type" content="text/html; charset=ISO-8859-1">
<title>Less-24 - Second Degree Injections </title>
</head>
<body bgcolor="#000000">
<div style="text-align:center">
<form name="login" method="POST" action="login.PHP">
<h2 style="text-align:center;background-image:url('../images/Less-24.jpg');background-repeat:no-repeat;background-position:center center">
<div style="padding-top:300px;text-align:center;color:#FFFF00;"><?PHP echo $form_title_in; ?></div>
</h2>
<div align="center">
<table style="margin-top:50px;">
<tr>
<td style="text-align:right">
<font size="3" color="#FFFF00">
<strong>Username:</strong>
</td>
<td style="text-align:left">
<input name="login_user" id="login_user" type="text" value="" />
</td>
</tr>
<tr>
<td style="text-align:right">
<font size="3" color="#FFFF00">
<strong>Password:</strong>
</td>
<td style="text-align:left">
<input name="login_password" id="login_password" type="password" value="" />
</td>
</tr>
<tr>
<td colspan="2" style="text-align:right">
<input name="mysubmit" id="mysubmit" type="submit" value="Login" /><br/><br/>
<a style="font-size:.8em;color:#FFFF00" href="forgot_password.PHP">Forgot your password?</a><font size="3" color="#FFFF00">
||</font>
<a style="font-size:.8em;color:#FFFF00" href="new_user.PHP">New User click here?</a>
</td>
</tr>
</table>
</div>
</form>
</div>
</body>
</html>
login.PHP
<html>
<head>
</head>
<body bgcolor="#000000">
<font size="3" color="#FFFF00">
<div align="right">
<a style="font-size:.8em;color:#FFFF00" href='index.PHP'><img src="../images/Home.png" height='45'; width='45'></br>HOME</a>
</div>
<?PHP
session_start();
//including the MysqL connect parameters.
include("../sql-connections/sql-connect.PHP");
function sqllogin(){
$username = MysqL_real_escape_string($_POST["login_user"]);
$password = MysqL_real_escape_string($_POST["login_password"]);
$sql = "SELECT * FROM users WHERE username='$username' and password='$password'";
//$sql = "SELECT COUNT(*) FROM users WHERE username='$username' and password='$password'";
$res = MysqL_query($sql) or die('You tried to be real smart, Try harder!!!! :( ');
$row = MysqL_fetch_row($res);
//print_r($row) ;
if ($row[1]) {
return $row[1];
} else {
return 0;
}
}
$login = sqllogin();
if (!$login== 0)
{
$_SESSION["username"] = $login;
setcookie("Auth", 1, time()+3600); /* expire in 15 Minutes */
header('Location: logged-in.PHP');
}
else
{
?>
<tr><td colspan="2" style="text-align:center;"><br/><p style="color:#FF0000;">
<center>
<img src="../images/slap1.jpg">
</center>
</p></td></tr>
<?PHP
}
?>
</body>
</html>
pass_change.PHP
<html>
<head>
</head>
<body bgcolor="#000000">
<?PHP
session_start();
if (!isset($_COOKIE["Auth"]))
{
if (!isset($_SESSION["username"]))
{
header('Location: index.PHP');
}
header('Location: index.PHP');
}
?>
<div align="right">
<a style="font-size:.8em;color:#FFFF00" href='index.PHP'><img src="../images/Home.png" height='45'; width='45'></br>HOME</a>
</div>
<?PHP
//including the MysqL connect parameters.
include("../sql-connections/sql-connect.PHP");
if (isset($_POST['submit']))
{
# Validating the user input........
$username= $_SESSION["username"];
$curr_pass= MysqL_real_escape_string($_POST['current_password']);
$pass= MysqL_real_escape_string($_POST['password']);
$re_pass= MysqL_real_escape_string($_POST['re_password']);
if($pass==$re_pass)
{
$sql = "UPDATE users SET PASSWORD='$pass' where username='$username' and password='$curr_pass' ";
$res = MysqL_query($sql) or die('You tried to be smart, Try harder!!!! :( ');
$row = MysqL_affected_rows();
echo '<font size="3" color="#FFFF00">';
echo '<center>';
if($row==1)
{
echo "Password successfully updated";
}
else
{
header('Location: Failed.PHP');
//echo 'You tried to be smart, Try harder!!!! :( ';
}
}
else
{
echo '<font size="5" color="#FFFF00"><center>';
echo "Make sure New Password and Retype Password fields have same value";
header('refresh:2, url=index.PHP');
}
}
?>
<?PHP
if(isset($_POST['submit1']))
{
session_destroy();
setcookie('Auth', 1 , time()-3600);
header ('Location: index.PHP');
}
?>
</center>
</body>
</html>
$sql = "UPDATE users SET PASSWORD='$pass' where username='$username' and password='$curr_pass' ";abcd'#
上面这条语句就会变成:
update users set password='aaaa' where username='abcd'# and password=xxxx
#把后面语句全部注释掉了
先插入数据——》再引用插入数据
防御:
过滤危险字符
采用PDO编程