SQL injection prevention in Flask - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to safely execute a SQL query using Flask and SQLite.

Flask

cursor.execute("SELECT * FROM users WHERE username = ?", ([1],))

Drag options to blanks, or click blank then click option'

Ainput

Buser_input

Cusername

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Putting the user input directly into the query string.

Using string concatenation to build the query.

Using parameterized queries with placeholders like ? and passing the user input as a tuple prevents SQL injection.

2fill in blank

medium

Complete the code to fetch the first result safely after executing a parameterized query.

Flask

result = cursor.[1]()

Drag options to blanks, or click blank then click option'

Afetchall

Bfetchone

Cfetchmany

Dexecute

Attempts:

3 left

💡 Hint

Common Mistakes

Using execute() instead of a fetch method.

Using fetchall() when only one result is needed.

fetchone() retrieves the first row of the query result safely.

3fill in blank

hard

Fix the error in the code to prevent SQL injection when inserting data.

Flask

cursor.execute("INSERT INTO users (username, password) VALUES ([1], [2])", (username, password))

Drag options to blanks, or click blank then click option'

A?

C:username

D:password

Eusername

Fpassword

Attempts:

3 left

💡 Hint

Common Mistakes

Putting quotes around placeholders.

Using named placeholders without proper syntax.

Use ? placeholders without quotes and separate them by commas to safely insert parameters.

4fill in blank

hard

Fill both blanks to create a safe SELECT query with named placeholders in Flask.

Flask

cursor.execute("SELECT * FROM users WHERE email = [1]", [2])

Drag options to blanks, or click blank then click option'

A:email

B{'email': email}

Cemail

D('email',)

Attempts:

3 left

💡 Hint

Common Mistakes

Using positional placeholders with a dictionary.

Passing parameters as a tuple with named placeholders.

Named placeholders like :email are used in the query string, and a dictionary with the key 'email' maps to the variable email.

5fill in blank

hard

Fill all three blanks to safely update a user's password using parameterized queries.

Flask

cursor.execute("UPDATE users SET password = [1] WHERE username = [2]", ([3], username))

Drag options to blanks, or click blank then click option'

A?

B:password

Cnew_password

Dpassword

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing named and positional placeholders.

Passing variable names as strings instead of variables.

Use positional placeholders ? for both parameters and pass the new password variable in the tuple.

Practice

1. What is the main purpose of using parameterized queries in Flask when working with databases?

easy

A. To speed up database queries by caching results

B. To prevent SQL injection attacks by separating code from data

C. To allow users to write their own SQL commands

D. To automatically create database tables

Solution

1. Step 1: Understand SQL injection risk

   SQL injection happens when user input is treated as code, allowing attackers to change database commands.

2. Step 2: Role of parameterized queries

   Parameterized queries keep user data separate from SQL code, stopping attackers from injecting harmful commands.

3. Final Answer:

   To prevent SQL injection attacks by separating code from data -> Option B

4. Quick Check:

   SQL injection prevention = parameterized queries [OK]

Hint: Remember: separate data from code to stop injection [OK]

Common Mistakes:

• Thinking parameterized queries speed up queries
• Believing users can safely write SQL commands
• Confusing parameterized queries with table creation

2. Which of the following is the correct way to use parameterized queries with Flask's database cursor?

easy

A. cursor.execute(f"SELECT * FROM users WHERE id = {user_id}")

B. cursor.execute("SELECT * FROM users WHERE id = ?", (user_id,))

C. cursor.execute("SELECT * FROM users WHERE id = %s", (user_id,))

D. cursor.execute("SELECT * FROM users WHERE id = :id", user_id)

Solution

1. Step 1: Identify correct placeholder syntax

   In Flask with many DB adapters like psycopg2, %s is used as placeholder for parameters.

2. Step 2: Check parameter passing format

   Parameters must be passed as a tuple, e.g., (user_id,). cursor.execute("SELECT * FROM users WHERE id = %s", (user_id,)) uses %s and tuple correctly.

3. Final Answer:

   cursor.execute("SELECT * FROM users WHERE id = %s", (user_id,)) -> Option C

4. Quick Check:

   Use %s with tuple for parameters [OK]

Hint: Use %s and tuple for parameters in execute() [OK]

Common Mistakes:

• Using f-strings directly with user input
• Using ? placeholder which is for SQLite, not psycopg2
• Passing parameters incorrectly without tuple

3. Given this Flask code snippet, what will be the output if user_id = "1 OR 1=1" and parameterized queries are used correctly?

cursor.execute("SELECT * FROM users WHERE id = %s", (user_id,))
results = cursor.fetchall()
print(results)

medium

A. Only rows where id equals the string '1 OR 1=1' will be returned

B. All rows from users table will be returned

C. Syntax error due to SQL injection

D. No rows will be returned because of wrong query

Solution

1. Step 1: Understand parameterized query effect

   Parameterized queries treat user input as data, not code, so "1 OR 1=1" is a string value, not SQL logic.

2. Step 2: Result of query with injected string

   The query looks for rows where id equals the string "1 OR 1=1", which likely matches no rows or only exact matches.

3. Final Answer:

   Only rows where id equals the string '1 OR 1=1' will be returned -> Option A

4. Quick Check:

   Parameterized input treated as data = Only rows where id equals the string '1 OR 1=1' will be returned [OK]

Hint: Parameterized input is data, not code, so no injection [OK]

Common Mistakes:

• Assuming injection runs and returns all rows
• Expecting syntax error from parameterized query
• Thinking query fails due to input format

4. Identify the error in this Flask code that tries to prevent SQL injection:

user_id = request.args.get('id')
cursor.execute("SELECT * FROM users WHERE id = %s" % user_id)
results = cursor.fetchall()

medium

A. Using wrong placeholder %s instead of ?

B. Missing parentheses in fetchall()

C. Not converting user_id to integer

D. Using string formatting instead of parameterized query

Solution

1. Step 1: Check how query is constructed

   The code uses string formatting (% operator) to insert user_id directly into the query string.

2. Step 2: Why this is wrong for injection prevention

   Direct string formatting allows malicious input to change SQL code, causing SQL injection risk.

3. Final Answer:

   Using string formatting instead of parameterized query -> Option D

4. Quick Check:

   Use parameterized queries, not string formatting [OK]

Hint: Never build queries with string formatting; use parameters [OK]

Common Mistakes:

• Thinking fetchall() needs parentheses fix
• Believing user_id must be int for injection safety
• Confusing %s and ? placeholders

5. You want to safely insert multiple user records into a database using Flask and prevent SQL injection. Which approach correctly combines parameterized queries with batch insertion?

users = [("alice", 25), ("bob", 30)]
cursor.executemany(??? , users)

What should replace ????

hard

A. "INSERT INTO users (name, age) VALUES (%s, %s)"

B. "INSERT INTO users (name, age) VALUES ('%s', '%s')"

C. "INSERT INTO users (name, age) VALUES (?, ?)"

D. "INSERT INTO users (name, age) VALUES (:name, :age)"

Solution

1. Step 1: Identify correct placeholder syntax for batch insert

   For executemany with psycopg2 or similar, %s placeholders are used without quotes.

2. Step 2: Check placeholder usage in options

   "INSERT INTO users (name, age) VALUES (%s, %s)" uses %s placeholders correctly; "INSERT INTO users (name, age) VALUES ('%s', '%s')" wrongly adds quotes, "INSERT INTO users (name, age) VALUES (?, ?)" uses ? (SQLite style), "INSERT INTO users (name, age) VALUES (:name, :age)" uses named placeholders which need dicts.

3. Final Answer:

   "INSERT INTO users (name, age) VALUES (%s, %s)" -> Option A

4. Quick Check:

   Use %s placeholders without quotes for executemany [OK]

Hint: Use %s placeholders without quotes for batch inserts [OK]

Common Mistakes:

• Adding quotes around %s placeholders
• Using ? placeholders with psycopg2
• Using named placeholders without dict parameters