A security administrator examines a network session to a compromised database server with a packet analyzer. Within the session there is a repeated series of the
hex character 90 (x90).
Which of the following attack types has occurred?

A.
Buffer overflow

B.
Cross-site scripting

C.
XML injection

D.
SQL injection

Explanation:
The hex character 90 (x90) means NOP or No Op or No Operation. In a buffer overflow attack, the buffer can be filled and overflowed with No Op commands. A
buffer overflow occurs when a program or process tries to store more data in a buffer (temporary data storage area) than it was intended to hold. Since buffers are
created to contain a finite amount of data, the extra information – which has to go somewhere – can overflow into adjacent buffers, corrupting or overwriting the valid

data held in them. Although it may occur accidentally through programming error, buffer overflow is an increasingly common type of security attack on data
integrity. In buffer overflow attacks, the extra data may contain codes designed to trigger specific actions, in effect sending new instructions to the attacked
computer that could, for example, damage the user’s files, change data, or disclose confidential information. Buffer overflow attacks are said to have arisen
because the C programming language supplied the framework, and poor programming practices supplied the vulnerability.
Incorrect Answers:
B: Cross-site scripting (XSS) is a type of computer security vulnerability typically found in Web applications. XSS enables attackers to inject client-side script into
Web pages viewed by other users.
Cross-site scripting uses known vulnerabilities in web-based applications, their servers, or plug- in systems on which they rely. Exploiting one of these, attackers
fold malicious content into the content being delivered from the compromised site. When the resulting combined content arrives at the client-side web browser, it
has all been delivered from the trusted source, and thus operates under the permissions granted to that system. By finding ways of injecting malicious scripts into
web pages, an attacker can gain elevated access-privileges to sensitive page content, session cookies, and a variety of other information maintained by the
browser on behalf of the user. A repeated series of the hex character 90 is not an example of an XSS attack. Therefore, this answer is incorrect.
C: When a web user takes advantage of a weakness with SQL by entering values that they should not, it is known as a SQL injection attack. Similarly, when the
user enters values that query XML (known as XPath) with values that take advantage of exploits, it is known as an XML injection attack. XPath works in a similar
manner to SQL, except that it does not have the same levels of access control, and taking advantage of weaknesses within can return entire documents. The best
way to prevent XML injection attacks is to filter the user’s input and sanitize it to make certain that it does not cause XPath to return more data than it should. A
repeated series of the hex character 90 is not an example of XML injection. Therefore, this answer is incorrect.
D: SQL injection is a code injection technique, used to attack data-driven applications, in which malicious SQL statements are inserted into an entry field for
execution (e.g. to dump the database contents to the attacker). SQL injection must exploit a security vulnerability in an application’s software, for example, when
user input is either incorrectly filtered for string literal escape characters embedded in SQL statements or user input is not strongly typed and unexpectedly
executed. SQL injection is mostly known as an attack vector for websites but can be used to attack any type of SQL database. A repeated series of the hex
character 90 is not an example of SQL injection. Therefore, this answer is incorrect.

http://searchsecurity.techtarget.com/definition/buffer-overflow http://en.wikipedia.org/wiki/Cross-site_scripting
Dulaney, Emmett and Chuck Eastton, CompTIA Security+ Study Guide, Sixth Edition, Sybex, Indianapolis, 2014, p 337
http://en.wikipedia.org/wiki/SQL_injection