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Consider the following PHP script:

<?php 
echo "Welcome, {$_POST['name']}."; 
?>

What type of attack is possible with this PHP script?

Replay attack

escapeshellarg()

Cross-site scripting attack

SQL injection attack

Explanation:

Answer option C is correct.

This script is vulnerable to the cross-site scripting attack. Cross Site Scripting vulnerabilities or XSS flaws arise every time an application takes a user-supplied data and sends it to a Web browser without first confirming or encoding the content. A number of times attackers find these flaws in Web applications. XSS flaws allow an attacker to execute a script in the victim's browser, allowing him to take control of user sessions, disfigure Web sites, and possibly launch worms, viruses, malware, etc. to steal and access critical data from the user's database.

Answer option D is incorrect. An SQL injection attack is a process in which an attacker tries to execute unauthorized SQL statements. These statements can be used to delete data from a database, delete database objects such as tables, views, stored procedures, etc. An attacker can either directly enter the code into input variables or insert malicious code in strings that can be stored in a database.

For example, the following line of code illustrates one form of an SQL injection attack:

query = "SELECT * FROM users WHERE name = '" + userName + "';"

This SQL code is designed to fetch the records of any specified username from its table of users. However, if the "userName" variable is crafted in a specific way by a malicious hacker, the SQL statement may do more than the code author intended.

For example, if the attacker puts the "userName" value as ' or ''=', the SQL statement will be as follows:

SELECT * FROM users WHERE name = '' OR ''='';

The following is an example of a normal SQL query:

Select * from mytable where user name = 'Mark' and password =`12345`;

Example: Code analysis

A user enters a user name and password that matches a record in the table. The number of matched rows is retrieved using a dynamically generated SQL query. The user is then authenticated and redirected to the requested page. The SQL query will look like as follows when the attacker enters blah' or 1=1--:

SELECT Count (*) FROM
Users WHERE
UserName= 'blah' Or 1=1 --
' AND Password=' '

The query simply becomes as follows because a pair of hyphens designate the beginning of a comment in SQL:

SELECT Count(*) FROM
Users WHERE
UserName= 'blah' Or 1=1

The following is an example of SQL injection query:

Select * from mytable where user name = ''OR 1=1; --' and password=`dummy`;

The following attacks are performed by SQL injection based on the application and how it processes user-supplied data:
Authentication bypass: In this attack, an attacker can log onto an application and gain administrative privileges. The attacker does not even need to provide a valid username and password.
Information disclosure: In this attack, an attacker obtains sensitive information stored in the database.
Compromised data integrity: In this attack, an attacker defaces a webpage, inserts malicious content into web pages, or changes the content of a database.
Compromised availability of data: In this attack, an attacker deletes the information, deletes log, or audits information that is included in a database.
Remote code execution: In this attack, an attacker can compromise the host operating system.

Answer option A is incorrect. A replay attack is a type of attack in which attackers capture packets containing passwords or digital signatures whenever packets pass between two hosts on a network. In an attempt to obtain an authenticated connection, the attackers then resend the captured packet to the system. In this type of attack, the attacker does not know the actual password, but can simply replay the captured packet.

Answer option B is incorrect. This is not an attack but a function to prevent from SQL injection attack.