How SQL injection exploits queries - Quick Revision & Summary

Recall & Review

beginner

What is SQL injection?

SQL injection is a security attack where an attacker inserts malicious SQL code into a query to manipulate the database.

beginner

How does SQL injection exploit a query?

It exploits queries by inserting extra SQL commands into input fields that are not properly checked, changing the query's behavior.

beginner

Why is using user input directly in SQL queries dangerous?

Because attackers can add SQL code in the input, which the database runs, leading to data leaks or damage.

intermediate

What is a common way to prevent SQL injection?

Use prepared statements or parameterized queries that separate code from data, so input can't change query structure.

intermediate

Example: What happens if input is ' OR '1'='1 in a login query?

It changes the query to always be true, letting attackers bypass login without a password.

What does SQL injection allow an attacker to do?

A Run unauthorized SQL commands

B Speed up database queries

C Encrypt database data

D Backup the database automatically

SQL injection lets attackers run unauthorized SQL commands by inserting malicious code.

Which practice helps prevent SQL injection?

A Using prepared statements

B Allowing all user input directly

C Disabling database logs

D Using plain text passwords

Prepared statements separate code from data, stopping malicious input from changing queries.

What is a sign of a vulnerable SQL query?

A Using parameterized queries

B Directly inserting user input into the query string

C Encrypting user passwords

D Limiting database access

Directly inserting user input without checks can let attackers inject SQL code.

What can happen if SQL injection is successful?

A Improved database security

B Faster query execution

C Data theft or deletion

D Automatic data backup

Attackers can steal or delete data by exploiting SQL injection vulnerabilities.

Which input could be used in SQL injection to bypass login?

A password123

B SELECT * FROM users

C DROP TABLE users

D ' OR '1'='1

The input ' OR '1'='1 changes the query logic to always true, bypassing login checks.

Explain how SQL injection exploits a database query.

Think about how attackers use input fields to change what the database does.

Describe methods to prevent SQL injection attacks.

Focus on how to keep code and data separate in queries.

Practice

1. What is the main risk of SQL injection attacks on a database?

easy

A. Slower query performance

B. Unauthorized access to or manipulation of data

C. Syntax errors in SQL queries

D. Increased storage space usage

Solution

1. Step 1: Understand what SQL injection does

   SQL injection allows attackers to insert malicious SQL code into queries to manipulate the database.

2. Step 2: Identify the main consequence

   This manipulation can lead to unauthorized access or changes to data, which is a serious security risk.

3. Final Answer:

   Unauthorized access to or manipulation of data -> Option B

4. Quick Check:

   SQL injection = Unauthorized data access [OK]

Hint: SQL injection lets attackers access or change data illegally [OK]

Common Mistakes:

• Confusing SQL injection with performance issues
• Thinking it only causes syntax errors
• Assuming it increases storage use

2. Which of the following SQL query snippets is vulnerable to SQL injection if user input is not sanitized?
SELECT * FROM users WHERE username = '" + userInput + "';

easy

A. SELECT * FROM users WHERE username = '" + userInput + "';

B. SELECT * FROM users WHERE username = ?;

C. SELECT * FROM users WHERE username = 'admin';

D. SELECT * FROM users WHERE username = 'admin' AND password = 'pass';

Solution

1. Step 1: Identify how user input is used

   The query concatenates userInput directly into the SQL string without sanitization.

2. Step 2: Recognize vulnerability

   This direct insertion allows attackers to inject malicious SQL code, making it vulnerable.

3. Final Answer:

   SELECT * FROM users WHERE username = '" + userInput + "'; -> Option A

4. Quick Check:

   Direct input concatenation = Vulnerable [OK]

Hint: Directly adding user input to query string is unsafe [OK]

Common Mistakes:

• Choosing parameterized queries as vulnerable
• Confusing safe hardcoded queries with vulnerable ones
• Ignoring the role of input sanitization

3. Given the vulnerable query:
SELECT * FROM users WHERE username = '" + userInput + "';
If userInput is admin' OR '1'='1, what will the query become and what is the likely result?

medium

A. Syntax error due to unmatched quotes

B. SELECT * FROM users WHERE username = 'admin OR 1=1'; -- Returns no users

C. SELECT * FROM users WHERE username = 'admin'; -- Returns only admin user

D. SELECT * FROM users WHERE username = 'admin' OR '1'='1'; -- Returns all users

Solution

1. Step 1: Substitute userInput into the query

   The query becomes: SELECT * FROM users WHERE username = 'admin' OR '1'='1';

2. Step 2: Understand the effect of OR '1'='1'

   The condition '1'='1' is always true, so the WHERE clause matches all rows.

3. Final Answer:

   SELECT * FROM users WHERE username = 'admin' OR '1'='1'; -- Returns all users -> Option D

4. Quick Check:

   Injected OR '1'='1' returns all rows [OK]

Hint: OR '1'='1' always true returns all rows [OK]

Common Mistakes:

• Thinking it causes syntax error
• Assuming it returns only admin user
• Misreading the injected condition

4. You have this vulnerable SQL query in your code:
query = "SELECT * FROM users WHERE username = '" + userInput + "';"
Which fix correctly prevents SQL injection?

medium

A. Remove the WHERE clause entirely

B. Escape single quotes in userInput manually

C. Use parameterized queries or prepared statements

D. Convert userInput to uppercase before using

Solution

1. Step 1: Identify secure coding practice

   Parameterized queries separate code from data, preventing injection.

2. Step 2: Evaluate other options

   Manual escaping is error-prone, removing WHERE breaks logic, uppercase conversion doesn't prevent injection.

3. Final Answer:

   Use parameterized queries or prepared statements -> Option C

4. Quick Check:

   Parameterized queries = Safe from injection [OK]

Hint: Always use parameterized queries to stop injection [OK]

Common Mistakes:

• Relying on manual escaping only
• Removing query conditions instead of fixing
• Thinking input case changes prevent injection

5. Consider a login system using this vulnerable query:
SELECT * FROM users WHERE username = '" + userInput + "' AND password = '" + passInput + "';
If an attacker inputs admin' -- as username and anything as password, what happens and why?

hard

A. Login succeeds without password check because -- comments out rest

B. Login fails due to syntax error from unmatched quotes

C. Login succeeds only if password matches exactly

D. Login fails because input is rejected by the system

Solution

1. Step 1: Substitute attacker input into query

   The query becomes: SELECT * FROM users WHERE username = 'admin' --' AND password = 'anything';

2. Step 2: Understand effect of -- comment

   The -- makes the rest of the query a comment, so password check is ignored.

3. Step 3: Result of query

   The query checks only username = 'admin', allowing login without password.

4. Final Answer:

   Login succeeds without password check because -- comments out rest -> Option A

5. Quick Check:

   -- comments out password check = Login bypass [OK]

Hint: SQL comment -- skips password check for login bypass [OK]

Common Mistakes:

• Assuming syntax error occurs
• Thinking password is still checked
• Believing input is blocked automatically