SQL Injection is a type of attack that exploits a vulnerability in a web application that uses a SQL database.
The attacker injects malicious SQL code into the user input, such as a login form, that is then executed by the database server. This can allow the attacker to access, modify, or delete data, or execute commands on the database server.
The 'UNION' SQL keyword is often used in SQL Injection attacks to combine the results of two or more SELECT statements into a single result set. This can allow the attacker to retrieve additional data from other tables or columns that are not intended to be displayed by the application. For example, if the application uses the following query to check the user credentials:
SELECT * FROM users WHERE username = '$username' AND password = '$password' The attacker can inject a 'UNION' statement to append another query, such as:
' OR 1 = 1 UNION SELECT * FROM credit_cards --
This will result in the following query being executed by the database server:
SELECT * FROM users WHERE username = '' OR 1 = 1 UNION SELECT * FROM credit_cards --' AND password = '$password' The first part of the query will always return true, and the second part of the query will return the data from the credit_cards table. The '-' symbol is a comment that will ignore the rest of the query. The attacker can then see the credit card information in the application's response.
However, some web applications implement security measures to prevent SQL Injection attacks, such as filtering special characters in user inputs. Special characters are symbols that have a special meaning in SQL, such as quotes, semicolons, dashes, etc. By filtering or escaping these characters, the application can prevent the attacker from injecting malicious SQL code. For example, if the application replaces single quotes with two single quotes, the previous injection attempt will fail, as the query will become:
SELECT * FROM users WHERE username = '''' OR 1 = 1 UNION SELECT * FROM credit_cards --'' AND password = '$password' This will result in a syntax error, as the query is not valid SQL.
In this challenging environment, if the hacker still intends to exploit this SQL Injection vulnerability, the strategy that he is most likely to employ is to bypass the special character filter by encoding his malicious input. Encoding is a process of transforming data into a different format, such as hexadecimal, base64, URL, etc. By encoding his input, the hacker can avoid the filter and still inject malicious SQL code. For example, if the hacker encodes his input using URL encoding, the previous injection attempt will become:
%27%20OR%201%20%3D%201%20UNION%20SELECT%20*%20FROM%20credit_cards%20--
This will result in the following query being executed by the database server, after the application decodes the input:
SELECT * FROM users WHERE username = '' OR 1 = 1 UNION SELECT * FROM credit_cards --' AND password = '$password' This will succeed in returning the credit card information, as the filter will not detect the special characters in the encoded input.
Therefore, the hacker is most likely to employ the strategy of bypassing the special character filter by encoding his malicious input, which could potentially enable him to successfully inject damaging SQL queries.
References:
SQL Injection | OWASP Foundation
SQL Injection Union Attacks
SQL Injection Bypassing WAF

This scenario clearly describes the need for Time-Based Blind SQL Injection, an advanced SQL injection technique covered in the CEH v13 Web Application Hacking module. Blind SQL injection is used when an application does not return database errors or visible output, making traditional techniques ineffective.
According to CEH v13, Time-Based Blind SQL Injection is particularly useful when:
* The backend database type is unknown
* Error messages are suppressed
* UNION queries fail
* No direct data is returned in responses
In this technique, attackers inject SQL statements that deliberately introduce time delays using database- specific functions such as SLEEP(), WAITFOR DELAY, or BENCHMARK(). The ethical hacker then observes the application's response time to determine whether the injected condition is true or false.
For example:
' OR IF(1=1, SLEEP(5), 0) --
If the application response is delayed, it confirms that the injected SQL statement was executed successfully.
CEH v13 categorizes this method as behavioral-based inference, where the attacker extracts information one bit at a time by analyzing timing differences.
Other options are incorrect because:
* Content-Based Blind SQL Injection relies on visible differences in responses, which the question states are unavailable.
* Union-Based SQL Injection requires knowing column count and data types.
* Error-Based SQL Injection depends on database error messages being displayed.
CEH v13 emphasizes Time-Based Blind SQL Injection as a last-resort yet highly effective technique when dealing with hardened applications that suppress output, making it a frequent exam-tested concept.

Steganalysis tools are specifically designed to detect hidden data within media files by analyzing anomalies in file structure and content, making them the most effective means to uncover and counter data exfiltration conducted through steganography.

The CEH SQL Injection module defines stacked (piggybacked) queries as attacks where an attacker appends an additional SQL statement using a statement delimiter such as a semicolon.
In this scenario, the attacker executed a second query (DROP TABLE users) after the original query, resulting in destructive behavior.
Option B is correct.
Option A retrieves data, not execute destructive commands.
Option C infers logic outcomes.
Option D relies on error messages for data extraction.
CEH classifies stacked queries as high-impact SQL injection attacks.