Description
1 Overview
SQL injection is a code injection technique that exploits the vulnerabilities in the interface between web
applications and database servers. The vulnerability is present when user’s inputs are not correctly checked
within the web applications before being sent to the back-end database servers.
Many web applications take inputs from users, and then use these inputs to construct SQL queries, so
they can get information from the database. Web applications also use SQL queries to store information in
the database. These are common practices in the development of web applications. When SQL queries are
not carefully constructed, SQL injection vulnerabilities can occur. SQL injection is one of the most common
attacks on web applications.
In this lab, we have created a web application that is vulnerable to the SQL injection attack. Our web
application includes the common mistakes made by many web developers. Students’ goal is to find ways to
exploit the SQL injection vulnerabilities, demonstrate the damage that can be achieved by the attack, and
master the techniques that can help defend against such type of attacks. This lab covers the following topics:
• SQL statement: SELECT and UPDATE statements
• SQL injection
• Prepared statement
Readings. Detailed coverage of the SQL injection can be found in the following:
• Chapter 12 of the SEED Book, Computer & Internet Security: A Hands-on Approach, 2nd Edition,
by Wenliang Du. See details at https://www.handsonsecurity.net.
Lab Environment. This lab has been tested on our pre-built Ubuntu 16.04 VM, which can be downloaded
from the SEED website.
2 Lab Environment
We have developed a web application for this lab. The folder where the application is installed and the URL
to access this web application are described in the following:
URL: http://www.SEEDLabSQLInjection.com
Folder: /var/www/SQLInjection/
The above URL is is only accessible from inside of the virtual machine, because we have modified
the /etc/hosts file to map the domain name of each URL to the virtual machine’s local IP address
(127.0.0.1). You may map any domain name to a particular IP address using /etc/hosts. For
example, you can map http://www.example.com to the local IP address by appending the following
entry to /etc/hosts:
SEED Labs – SQL Injection Attack Lab 2
127.0.0.1 www.example.com
If your web server and browser are running on two different machines, you need to modify /etc/hosts
on the browser’s machine accordingly to map these domain names to the web server’s IP address, not to
127.0.0.1.
Apache Configuration. In our pre-built VM image, we used Apache server to host all the web sites used
in the lab. The name-based virtual hosting feature in Apache could be used to host several web sites (or
URLs) on the same machine. A configuration file named 000-default.conf in the directory “/etc/
apache2/sites-available” contains the necessary directives for the configuration:
Inside the configuration file, each web site has a VirtualHost block that specifies the URL for the
web site and directory in the file system that contains the sources for the web site. The following examples
show how to configure a website with URL http://www.example1.com and another website with
URL http://www.example2.com:
ServerName http://www.example1.com
DocumentRoot /var/www/Example_1/
ServerName http://www.example2.com
DocumentRoot /var/www/Example_2/
You may modify the web application by accessing the source in the mentioned directories. For example, with the above configuration, the web application http://www.example1.com can be changed by
modifying the sources in the /var/www/Example_1/ directory. After a change is made to the configuration, the Apache server needs to be restarted. See the following command:
$ sudo service apache2 start
3 Lab Tasks
We have created a web application, and host it at www.SEEDLabSQLInjection.com. This web application is a simple employee management application. Employees can view and update their personal
information in the database through this web application. There are mainly two roles in this web application: Administrator is a privilege role and can manage each individual employees’ profile information;
Employee is a normal role and can view or update his/her own profile information. All employee information is described in the following table.
Name Employee ID Password Salary Birthday SSN Nickname Email Address Phone#
Admin 99999 seedadmin 400000 3/5 43254314
Alice 10000 seedalice 20000 9/20 10211002
Boby 20000 seedboby 50000 4/20 10213352
Ryan 30000 seedryan 90000 4/10 32193525
Samy 40000 seedsamy 40000 1/11 32111111
Ted 50000 seedted 110000 11/3 24343244
SEED Labs – SQL Injection Attack Lab 3
3.1 Task 1: Get Familiar with SQL Statements
The objective of this task is to get familiar with SQL commands by playing with the provided database. We
have created a database called Users, which contains a table called credential; the table stores the
personal information (e.g. eid, password, salary, ssn, etc.) of every employee. In this task, you need to play
with the database to get familiar with SQL queries.
MySQL is an open-source relational database management system. We have already setup MySQL in
our SEEDUbuntu VM image. The user name is root and password is seedubuntu. Please login to
MySQL console using the following command:
$ mysql -u root -pseedubuntu
After login, you can create new database or load an existing one. As we have already created the Users
database for you, you just need to load this existing database using the following command:
mysql> use Users;
To show what tables are there in the Users database, you can use the following command to print out
all the tables of the selected database.
mysql> show tables;
After running the commands above, you need to use a SQL command to print all the profile information
of the employee Alice. Please provide the screenshot of your results.
3.2 Task 2: SQL Injection Attack on SELECT Statement
SQL injection is basically a technique through which attackers can execute their own malicious SQL statements generally referred as malicious payload. Through the malicious SQL statements, attackers can steal
information from the victim database; even worse, they may be able to make changes to the database. Our
employee management web application has SQL injection vulnerabilities, which mimic the mistakes frequently made by developers.
We will use the login page from www.SEEDLabSQLInjection.com for this task. The login page
is shown in Figure 1. It asks users to provide a user name and a password. The web application authenticate
users based on these two pieces of data, so only employees who know their passwords are allowed to log in.
Your job, as an attacker, is to log into the web application without knowing any employee’s credential.
To help you started with this task, we explain how authentication is implemented in the web application.
The PHP code unsafe home.php, located in the /var/www/SQLInjection directory, is used to
conduct user authentication. The following code snippet show how users are authenticated.
$input_uname = $_GET[’username’];
$input_pwd = $_GET[’Password’];
$hashed_pwd = sha1($input_pwd);
…
$sql = “SELECT id, name, eid, salary, birth, ssn, address, email,
nickname, Password
FROM credential
WHERE name= ’$input_uname’ and Password=’$hashed_pwd’”;
$result = $conn -> query($sql);
// The following is Pseudo Code
if(id != NULL) {
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Figure 1: The Login page
if(name==’admin’) {
return All employees information;
} else if (name !=NULL){
return employee information;
}
} else {
Authentication Fails;
}
The above SQL statement selects personal employee information such as id, name, salary, ssn etc from
the credential table. The SQL statement uses two variables input uname and hashed pwd, where
input uname holds the string typed by users in the username field of the login page, while hashed pwd
holds the sha1 hash of the password typed by the user. The program checks whether any record matches
with the provided username and password; if there is a match, the user is successfully authenticated, and is
given the corresponding employee information. If there is no match, the authentication fails.
• Task 2.1: SQL Injection Attack from webpage. Your task is to log into the web application as the
administrator from the login page, so you can see the information of all the employees. We assume
that you do know the administrator’s account name which is admin, but you do not the password.
You need to decide what to type in the Username and Password fields to succeed in the attack.
• Task 2.2: SQL Injection Attack from command line. Your task is to repeat Task 2.1, but you
need to do it without using the webpage. You can use command line tools, such as curl, which
can send HTTP requests. One thing that is worth mentioning is that if you want to include multiple
parameters in HTTP requests, you need to put the URL and the parameters between a pair of single
quotes; otherwise, the special characters used to separate parameters (such as &) will be interpreted by
the shell program, changing the meaning of the command. The following example shows how to send
an HTTP GET request to our web application, with two parameters (username and Password)
attached:
$ curl
SEED Labs – SQL Injection Attack Lab 5
’www.SeedLabSQLInjection.com/index.php?username=alice&Password=111’
If you need to include special characters in the username or Password fields, you need to encode
them properly, or they can change the meaning of your requests. If you want to include single quote
in those fields, you should use %27 instead; if you want to include white space, you should use %20.
In this task, you do need to handle HTTP encoding while sending requests using curl.
• Task 2.3: Append a new SQL statement. In the above two attacks, we can only steal information
from the database; it will be better if we can modify the database using the same vulnerability in the
login page. An idea is to use the SQL injection attack to turn one SQL statement into two, with the
second one being the update or delete statement. In SQL, semicolon (;) is used to separate two SQL
statements. Please describe how you can use the login page to get the server run two SQL statements.
Try the attack to delete a record from the database, and describe your observation.
3.3 Task 3: SQL Injection Attack on UPDATE Statement
If a SQL injection vulnerability happens to an UPDATE statement, the damage will be more severe, because attackers can use the vulnerability to modify databases. In our Employee Management application,
there is an Edit Profile page (Figure 2) that allows employees to update their profile information, including
nickname, email, address, phone number, and password. To go to this page, employees need to log in first.
When employees update their information through the Edit Profile page, the following SQL UPDATE
query will be executed. The PHP code implemented in unsafe edit backend.php file is used to update employee’s profile information. The PHP file is located in the /var/www/SQLInjection directory.
$hashed_pwd = sha1($input_pwd);
$sql = “UPDATE credential SET
nickname=’$input_nickname’,
email=’$input_email’,
address=’$input_address’,
Password=’$hashed_pwd’,
PhoneNumber=’$input_phonenumber’
WHERE ID=$id;”;
$conn->query($sql);
• Task 3.1: Modify your own salary. As shown in the Edit Profile page, employees can only update
their nicknames, emails, addresses, phone numbers, and passwords; they are not authorized to change
their salaries. Assume that you (Alice) are a disgruntled employee, and your boss Boby did not
increase your salary this year. You want to increase your own salary by exploiting the SQL injection
vulnerability in the Edit-Profile page. Please demonstrate how you can achieve that. We assume that
you do know that salaries are stored in a column called ’salary’.
• Task 3.2: Modify other people’ salary. After increasing your own salary, you decide to punish your
boss Boby. You want to reduce his salary to 1 dollar. Please demonstrate how you can achieve that.
• Task 3.3: Modify other people’ password. After changing Boby’s salary, you are still disgruntled,
so you want to change Boby’s password to something that you know, and then you can log into his
account and do further damage. Please demonstrate how you can achieve that. You need to demonstrate that you can successfully log into Boby’s account using the new password. One thing worth
SEED Labs – SQL Injection Attack Lab 6
Figure 2: The Edit-Profile page
mentioning here is that the database stores the hash value of passwords instead of the plaintext password string. You can again look at the unsafe edit backend.php code to see how password is
being stored. It uses SHA1 hash function to generate the hash value of password.
To make sure your injection string does not contain any syntax error, you can test your injection string
on MySQL console before launching the real attack on our web application.
3.4 Task 4: Countermeasure — Prepared Statement
The fundamental problem of the SQL injection vulnerability is the failure to separate code from data. When
constructing a SQL statement, the program (e.g. PHP program) knows which part is data and which part
is code. Unfortunately, when the SQL statement is sent to the database, the boundary has disappeared; the
boundaries that the SQL interpreter sees may be different from the original boundaries that was set by the
developers. To solve this problem, it is important to ensure that the view of the boundaries are consistent in
the server-side code and in the database. The most secure way is to use prepared statement.
To understand how prepared statement prevents SQL injection, we need to understand what happens
when SQL server receives a query. The high-level workflow of how queries are executed is shown in
Figure 3. In the compilation step, queries first go through the parsing and normalization phase, where a query
is checked against the syntax and semantics. The next phase is the compilation phase where keywords (e.g.
SELECT, FROM, UPDATE, etc.) are converted into a format understandable to machines. Basically, in this
phase, query is interpreted. In the query optimization phase, the number of different plans are considered to
execute the query, out of which the best optimized plan is chosen. The chosen plan is store in the cache, so
whenever the next query comes in, it will be checked against the content in the cache; if it’s already present
in the cache, the parsing, compilation and query optimization phases will be skipped. The compiled query
is then passed to the execution phase where it is actually executed.
Prepared statement comes into the picture after the compilation but before the execution step. A prepared statement will go through the compilation step, and be turned into a pre-compiled query with empty
placeholders for data. To run this pre-compiled query, data need to be provided, but these data will not go
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Parsing & Normalization
Phase
Compilation Phase
Query Optimization
Phase
Execution Phase
Compilation
Execution
In this state, the SQL statement is
pre‐compiled into binary. Only
placeholders for data are included in
the prepared statement, not the
actual data. Data will be binded to
this statement later as pure data (so
no more compilation will be
conducted).
SQL Statement Execution Phases
Cache
Figure 3: Prepared Statement Workflow
through the compilation step; instead, they are plugged directly into the pre-compiled query, and are sent
to the execution engine. Therefore, even if there is SQL code inside the data, without going through the
compilation step, the code will be simply treated as part of data, without any special meaning. This is how
prepared statement prevents SQL injection attacks.
Here is an example of how to write a prepared statement in PHP. We use a SELECT statment in the
following example. We show how to use prepared statement to rewrite the code that is vulnerable to SQL
injection attacks.
$sql = “SELECT name, local, gender
FROM USER_TABLE
WHERE id = $id AND password =’$pwd’ “;
$result = $conn->query($sql))
The above code is vulnerable to SQL injection attacks. It can be rewritten to the following
$stmt = $conn->prepare(“SELECT name, local, gender
FROM USER_TABLE
WHERE id = ? and password = ? “);
// Bind parameters to the query
$stmt->bind_param(“is”, $id, $pwd);
$stmt->execute();
$stmt->bind_result($bind_name, $bind_local, $bind_gender);
$stmt->fetch();
Using the prepared statement mechanism, we divide the process of sending a SQL statement to the
database into two steps. The first step is to only send the code part, i.e., a SQL statement without the actual
the data. This is the prepare step. As we can see from the above code snippet, the actual data are replaced
by question marks (?). After this step, we then send the data to the database using bind param(). The
database will treat everything sent in this step only as data, not as code anymore. It binds the data to the
corresponding question marks of the prepared statement. In the bind param() method, the first argument
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“is” indicates the types of the parameters: “i” means that the data in $id has the integer type, and “s”
means that the data in $pwd has the string type.
For this task, please use the prepared statement mechanism to fix the SQL injection vulnerabilities
exploited by you in the previous tasks. Then, check whether you can still exploit the vulnerability or not.
4 Guidelines
Test SQL Injection String. In real-world applications, it may be hard to check whether your SQL injection attack contains any syntax error, because usually servers do not return this kind of error messages. To
conduct your investigation, you can copy the SQL statement from php source code to the MySQL console.
Assume you have the following SQL statement, and the injection string is ’ or 1=1;#.
SELECT * from credential
WHERE name=’$name’ and password=’$pwd’;
You can replace the value of $name with the injection string and test it using the MySQL console. This
approach can help you to construct a syntax-error free injection string before launching the real injection
attack.
5 Submission
You need to submit a detailed lab report, with screenshots, to describe what you have done and what you
have observed. You also need to provide explanation to the observations that are interesting or surprising.
Please also list the important code snippets followed by explanation. Simply attaching code without any
explanation will not receive credits.