SQL injection and buffer overflows are hacking techniques used to exploit weaknesses in applications

ITEC403 Graduation Project
Applications’ Security – Cem Yağlı

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Application Vulnerabilities
SQL injection and buffer overflows are
hacking techniques used to exploit
weaknesses in applications.
When programs are written, some
parameters used in the creation of the
application code can leave weaknesses
in the program.

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 SQL injection and buffer overflows are methods used to attack
application and are generally caused by programming flaws.
 SQL injection is a hacking method used to attack SQL databases
 Buffer overflows can exist in many different types of applications.
 SQL injection and buffer overflows are similar exploits in that they’re
both usually delivered via a user input field.
 The input field is
– where a user may enter a username and password on a website,
– add data to a URL,
– or perform a search for a keyword in another application.

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 Both SQL Server injection and buffer overflow
vulnerabilities are caused by the same issue:
– invalid parameters that are not verified by the application.
 If programmers don’t take the time to validate the
variables a user can enter into a variable field, the
results can be serious and unpredictable.
 Sophisticated hackers can exploit this vulnerability,
causing an execution fault and shutdown of the
system or application, or a command shell to be
executed for the hacker.

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 SQL injection and buffer overflow
countermeasures are designed to utilize
secure programming methods.
 By changing the variables used by the
application code, weaknesses in applications
can be greatly minimized.

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SQL Injection
 Generally, the purpose of SQL injection is
to convince the application to run SQL code
that was not intended.
 SQL injection occurs when an application
processes user-provided data to create a
SQL statement without first validating the
input.

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SQL Injection
 The user input is then submitted to a web
application database server for execution.
 When successfully exploited, SQL injection
can give an attacker access to database
content or allow the hacker to remotely
execute system commands.
 In the worst-case scenario, the hacker can
take control of the server that is hosting the
database.

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SQL Injection
 This exploit can give a hacker access to a remote shell
into the server file system.
 The impact of a SQL injection attacks depends on
– where the vulnerability is in the code,
– how easy it is to exploit the vulnerability,
– what level of access the application has to the database.
 Theoretically, SQL injection can occur in any type of
application, but it is most commonly associated with
web applications.
 The web applications are easy targets because by their
very nature they are open to being accessed from the
Internet.

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SQL Injection
 During a web application SQL injection attack,
– The malicious code is inserted into a web form field
– Or the website’s code to make a system execute a
command shell
– Or other arbitrary commands.
 Just as a legitimate user enters queries and
additions to the SQL database via a web form,
 The hacker can insert commands to the SQL Server
through the same web form field.

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SQL Injection
 For example:
– An arbitrary command from a hacker might open a
command prompt
– or display a table from the database.
 A database table may contain personal information
such as credit card numbers, social security
numbers, or passwords.
 SQL Servers are very common database servers
and used by many organizations to store confidential
data.
 This makes a SQL Server a high-value target and
therefore a system that is very attractive to hackers.

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Finding a SQL Injection Vulnerability
 Before launching a SQL injection attack, the hacker
determines whether the configuration of the
database and related tables and variables is
vulnerable.
 The steps to determine the SQL Server’s
vulnerability are as follows:
1. Using your web browser, search for a website that
uses a login page or other database input or query
fields (such as an “I forgot my password” form).
Look for web pages that display the POST or GET
HTML commands by checking the site’s source code.

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2.Test the SQL Server using single quotes (‘’).
Doing so indicates whether the user input
variable is sanitized or interpreted literally by the
server.
If the server responds with an error message
that says use 'a'='a' (or something similar),
then it’s most likely susceptible to a SQL
injection attack.
3. Use the SELECT command to retrieve data
from the database or the INSERT command to
add information to the database.

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 Here are some examples of variable field
text you can use on a web form to test for
SQL vulnerabilities:
– Blah’ or 1=1--
– Login:blah’ or 1=1--
– Password::blah’ or 1=1--
– http://search/index.asp?id=blah’ or 1=1--

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 These commands and similar variations may allow a
user to bypass a login depending on the structure
of the database.
 When entered in a form field, the commands may
return many rows in a table or even an entire
database table because the SQL Server is
interpreting the terms literally.
 The double dashes near the end of the command
tell SQL to ignore the rest of the command as a
comment.

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 Here are some examples of how to use SQL
commands to take control:
 To get a directory listing, type the following in a form
field:
– Blah‘;exec master..xp_cmdshell “dir c:*.* /s >c:directory.txt”--
 To create a file, type the following in a form field:
– Blah‘;exec master..xp_cmdshell “echo hacker-was-here > c:
hacker.txt”--
 To ping an IP address, type the following in a form
field:
– Blah‘;exec master..xp_cmdshell “ping 192.168.1.1”--

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The Purpose of SQL Injection
 SQL injection attacks are used by hackers to
achieve certain results. Some SQL exploits
will produce valuable user data stored in the
database, and some are just precursors to
other attacks.
 The following are the most common
purposes of a SQL injection attack:

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 Identifying SQL Injection Vulnerability
– The purpose is to probe a web application to discover
which parameters and user input fields are vulnerable
to SQL injection.
 Performing Database Finger-Printing
– The purpose is to discover the type and version of
database that a web application is using and
“fingerprint” the database.
– Knowing the type and version of the database used by
a web application allows an attacker to craft database
specific attacks.

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 Determining Database Schema
– To correctly extract data from a database, the attacker
often needs to know database schema information, such
as table names, column names, and column data types.
– This information can be used in a follow-on attack.
 Extracting Data
– These types of attacks employ techniques that will
extract data values from the database.
– Depending on the type of web application, this
information could be sensitive and highly desirable to
the attacker.

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 Adding or Modifying Data
– The purpose is to add or change information in a
database.
 Performing Denial of Service
– These attacks are performed to shut down access to a
web application, thus denying service to other users.
– Attacks involving locking or dropping database tables
also fall under this category.
 Evading Detection
– This category refers to certain attack techniques that are
employed to avoid auditing and detection.

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 Bypassing Authentication
– The purpose is to allow the attacker to bypass database and
application authentication mechanisms.
– Bypassing such mechanisms could allow the attacker to
assume the rights and privileges associated with another
application user.
 Executing Remote Commands
– These types of attacks attempt to execute arbitrary commands
on the database. These commands can be stored procedures
or functions available to database users.
 Performing Privilege Escalation
– These attacks take advantage of implementation errors or
logical flaws in the database in order to escalate the privileges
of the attacker.

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SQL Injection Using Dynamic Strings
 Many functions of a SQL database receive
static user input where the only variable is
the user input fields.
 Such statements do not change from
execution to execution.
 They are commonly called static SQL
statements.

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 Some programs must build and process a
variety of SQL statements at runtime.
 In many cases the full text of the statement
is unknown until application execution.
 Such statements can, and probably will,
change from execution to execution.
 So, they are called dynamic SQL
statements.

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 Dynamic SQL is an enhanced form of SQL
that, unlike standard SQL, facilitates the
automatic generation and execution of
program statements.
 Dynamic SQL is a term used to mean SQL
code that is generated by the web
application before it is executed.
 Dynamic SQL is a flexible and powerful
tool for creating SQL strings.

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 It can be helpful when you find it necessary
to write code that can adjust to varying
databases, conditions, or servers.
 Dynamic SQL also makes it easier to
automate tasks that are repeated many
times in a web application.
 A hacker can attack a web-based
authentication form using SQL injection
through the use of dynamic strings.

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 For example, the underlying code for a web
authentication form on a web server may
look like the following:
SQLCommand = “SELECT Username FROM Users WHERE Username =
‘“
SQLCommand = SQLComand & strUsername
SQLCommand = SQLComand & “‘ AND Password = ‘“
SQLCommand = SQLComand & strPassword
SQLCommand = SQLComand & “‘“
strAuthCheck = GetQueryResult(SQLQuery)

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 A hacker can exploit the SQL injection
vulnerability by entering a login and
password in the web form that uses the
following variables:
Username: kimberly
Password: graves’ OR ‘’=’

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 The SQL application would build a command
string from this input as follows:
SELECT Username FROM Users
WHERE Username = ‘kimberly’
AND Password = ‘graves’ OR ‘’=’’

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 This query will return all rows from the user’s
database, regardless of whether kimberly is a real
username in the database or graves is a legitimate
password.
 This is due to the OR statement appended to the
WHERE clause.
 The comparison ‘’=’’ will always return a true result,
making the overall WHERE clause evaluate to true
for all rows in the table.
 This will enable the hacker to log in with any
username and password.

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SQL Injection Vulnerability Scanning
 We can use the HP’s Scrawlr to test for SQL Injection
Vulnerabilities
1. Download Scrawlr from www.HP.com.
2. Install Scrawlr on your Windows lab PC.
3. Open the Scrawlr program.
4. Type a target web address in the URL Of Site To Scan field:
5. Click the Start button to start the audit of the website for SQL
injection vulnerabilities.
6. Once the SQL injection vulnerability scan is complete, Scrawlr
will display additional hosts linked from the scanned site.
It is a best practice to scan the linked sites as well as the main
site to ensure no SQL injection vulnerabilities exist.

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SQL Injection Countermeasures
 The cause of SQL injection vulnerabilities is
relatively simple and well understood:
– Insufficient validation of user input.
 To address this problem, defensive coding practices,
such as encoding user input and validation, can
be used when programming applications.
 It is a laborious and time-consuming process to
check all applications for SQL injection
vulnerabilities.

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 When implementing SQL injection countermeasures,
review source code for the following programming
weaknesses:
– Single quotes
– Lack of input validation
 The first countermeasures for preventing a SQL
injection attack are
– Minimizing the privileges of a user’s connection to the
database and
– Enforcing strong passwords for SA and Administrator
accounts.

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 You should also disable verbose or
explanatory error messages so no more
information than necessary is sent to the
hacker;
 Such information could help them determine
whether the SQL Server is vulnerable.

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 Another countermeasure for preventing SQL
injection is checking user data input and
validating the data prior to sending the input
to the application for processing.
 Some countermeasures to SQL injection are
– Rejecting known bad input
– Sanitizing and validating the input field

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Buffer Overflows
 As an ethical hacker;
– You must be able to identify different types of
buffer overflows.
– You should also know how to detect a buffer
overflow vulnerability and understand the
steps a hacker may use to perform a stack-
based overflow attack.

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Types of Buffer Overflows
 Buffer overflows are exploits that hackers
use against an operating system or
application;
 like SQL injection attacks, they’re usually
targeted at user input fields.
 A buffer overflow exploit causes
– a system to fail by overloading memory
– or executing a command shell
– or arbitrary code on the target system.

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 A buffer overflow vulnerability is caused by
– a lack of bounds checking
– or a lack of input-validation sanitization in a variable
field (such as on a web form).
 If the application doesn’t check or validate the size
or format of a variable before sending it to be stored
in memory, an overflow vulnerability exits.
 The two types of buffer overflows are
– stack based
– heap based.

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 The stack and the heap are storage locations for
user-supplied variables within a running program.
 Variables are stored in the stack or heap until the
program needs them.
– Stacks are static locations of memory address space.
– Heaps are dynamic memory address spaces that occur
while a program is running.
 A heap-based buffer overflow occurs in the lower
part of the memory and overwrites other dynamic
variables.

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 A call stack, or stack, is used to keep track of
where in the programming code the execution
pointer should return after each portion of the code
is executed.
 A stack-based buffer overflow attack occurs when
the memory assigned to each execution routine is
overflowed.
 As a consequence of both types of buffer overflows,
– A program can open a shell or
– command prompt or stop the execution of a program.

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 To detect program buffer overflow
vulnerabilities that result from poorly written
source code,
– a hacker sends large amounts of data to the
application via a form field
– and sees what the program does as a result.

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 The following are the steps a hacker uses to execute
a stack-based buffer overflow:
1. Enter a variable into the buffer to exhaust the amount of
memory in the stack.
2. Enter more data than the buffer has allocated in memory
for that variable, which causes the memory to overflow
or run into the memory space for the next process.
Then, add another variable, and overwrite the return
pointer that tells the program where to return to after
executing the variable.

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3. A program executes this malicious code variable and
then uses the return pointer to get back to the next
line of executable code.
If the hacker successfully overwrites the pointer, the
program executes the hacker’s code instead of the
program code.
 Most hackers don’t need to be this familiar with the
details of buffer overflows.
 Prewritten exploits can be found on the Internet
and are exchanged between hacker groups
(example: Metasploit).

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Buffer Overflow Countermeasures
 Hackers can graduate from standard buffer
overflows to redirecting the return pointer to the
code of their choosing.
 A hacker must know the exact memory address
and the size of the stack in order to make the
return pointer execute their code.
 A hacker can use a No Operation (NOP)
instruction, which is just padding to move the
instruction pointer and does not execute any code.
 The NOP instruction is added to a string before the
malicious code to be executed.

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 If an intrusion detection system (IDS) is present
on the network, it can thwart (not allowed) a hacker
who sends a series of NOP instructions to forward
to the instruction pointer.
 To bypass the IDS, the hacker can randomly
replace some of the NOP instructions with
equivalent pieces of code, such as x++,x-;?
NOPNOP.
 This example of a mutated buffer overflow attack
can bypass detection by an IDS.

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 Programmers should not use the built-in
strcpy(), strcat(), and streadd() C/C++
functions because they are susceptible to
buffer overflows.
 Alternatively, Java can be used as the
programming language since Java is not
susceptible to buffer overflows.

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