Secure headers configuration in Flask - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add a security header to the Flask response.

Flask

from flask import Flask, make_response
app = Flask(__name__)

@app.route('/')
def index():
    response = make_response('Hello, world!')
    response.headers['[1]'] = 'nosniff'
    return response

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

AStrict-Transport-Security

BContent-Security-Policy

CX-Frame-Options

DX-Content-Type-Options

Attempts:

3 left

💡 Hint

Common Mistakes

Using Content-Security-Policy header instead, which is for different security purpose.

Using X-Frame-Options which controls framing, not content sniffing.

The X-Content-Type-Options header with value nosniff prevents browsers from MIME-sniffing a response away from the declared content-type.

2fill in blank

medium

Complete the code to set the Content Security Policy header to allow only scripts from the same origin.

Flask

from flask import Flask, make_response
app = Flask(__name__)

@app.route('/')
def index():
    response = make_response('Hello, secure world!')
    response.headers['Content-Security-Policy'] = "script-src [1]"
    return response

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

A'unsafe-inline'

B'none'

C'self'

D'*'

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'none' which blocks all scripts including your own.

Using '*' which allows scripts from anywhere, reducing security.

The Content-Security-Policy header with script-src 'self' allows scripts only from the same origin, improving security.

3fill in blank

hard

Fix the error in setting the Strict-Transport-Security header to enforce HTTPS for 1 year.

Flask

from flask import Flask, make_response
app = Flask(__name__)

@app.route('/')
def index():
    response = make_response('Secure HTTPS!')
    response.headers['Strict-Transport-Security'] = 'max-age=[1]'
    return response

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

A3600

B31536000

C86400

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using 3600 which is only 1 hour.

Using 0 which disables the header.

The max-age value for Strict-Transport-Security is in seconds. 31536000 seconds equals 1 year.

4fill in blank

hard

Fill both blanks to add X-Frame-Options header to deny framing and set X-XSS-Protection header to block mode.

Flask

from flask import Flask, make_response
app = Flask(__name__)

@app.route('/')
def index():
    response = make_response('No framing and XSS protection')
    response.headers['[1]'] = 'DENY'
    response.headers['[2]'] = '1; mode=block'
    return response

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

AX-Frame-Options

BContent-Security-Policy

CX-XSS-Protection

DStrict-Transport-Security

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up header names and values.

Using Content-Security-Policy instead of X-Frame-Options for framing.

X-Frame-Options: DENY prevents the page from being framed to avoid clickjacking.
X-XSS-Protection: 1; mode=block enables the browser's XSS filter to block detected attacks.

5fill in blank

hard

Fill all three blanks to create a dictionary of security headers with correct keys and values.

Flask

security_headers = {
    '[1]': 'nosniff',
    '[2]': "script-src [3]"
}

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

AX-Content-Type-Options

BContent-Security-Policy

C'self'

DStrict-Transport-Security

Attempts:

3 left

💡 Hint

Common Mistakes

Using Strict-Transport-Security as a key for script-src policy.

Omitting quotes around 'self' in the policy value.

This dictionary sets X-Content-Type-Options to nosniff to prevent MIME sniffing, and Content-Security-Policy to allow scripts only from the same origin using script-src 'self'.

Practice

1. Which Flask feature is commonly used to add secure headers to every response?

easy

A. The @app.before_first_request decorator

B. The @app.route decorator

C. The @app.after_request decorator

D. The @app.teardown_request decorator

Solution

1. Step 1: Understand Flask request lifecycle

   Flask allows modifying responses after the view function runs using @app.after_request.

2. Step 2: Identify where headers are added

   Secure headers are added to the response object, which is accessible in @app.after_request.

3. Final Answer:

   The @app.after_request decorator -> Option C

4. Quick Check:

   Use @app.after_request to add headers [OK]

Hint: Add headers in @app.after_request for all responses [OK]

Common Mistakes:

• Using @app.route which only defines routes
• Trying to add headers in @app.before_first_request which runs once
• Using @app.teardown_request which is for cleanup, not response modification

2. Which of the following is the correct syntax to add a Content-Security-Policy header in Flask?

easy

A. response.set_header('Content-Security-Policy', "default-src 'self'")

B. response.header['Content-Security-Policy'] = "default-src 'self'"

C. response.headers.add('Content-Security-Policy', "default-src 'self'")

D. response.headers['Content-Security-Policy'] = "default-src 'self'"

Solution

1. Step 1: Recall Flask response header syntax

   Flask response headers are a dictionary-like object accessed via response.headers.

2. Step 2: Assign header value correctly

   Use response.headers['Header-Name'] = value to set or overwrite headers.

3. Final Answer:

   response.headers['Content-Security-Policy'] = "default-src 'self'" -> Option D

4. Quick Check:

   Headers set by assignment to response.headers [OK]

Hint: Use response.headers['Name'] = value to set headers [OK]

Common Mistakes:

• Using header instead of headers
• Trying to call set_header which Flask response lacks
• Using headers.add which is not a Flask method

3. Given this Flask code snippet, what will be the value of the X-Frame-Options header in the response?

from flask import Flask, Response
app = Flask(__name__)

@app.after_request
def add_headers(response: Response):
    response.headers['X-Frame-Options'] = 'DENY'
    return response

@app.route('/')
def home():
    return 'Hello'

medium

A. 'DENY'

B. 'SAMEORIGIN'

C. No X-Frame-Options header

D. 'ALLOW-FROM https://example.com'

Solution

1. Step 1: Check header assignment in @app.after_request

   The function sets X-Frame-Options to 'DENY' on every response.

2. Step 2: Confirm header presence in response

   Since the header is set unconditionally, the response will have X-Frame-Options: DENY.

3. Final Answer:

   'DENY' -> Option A

4. Quick Check:

   X-Frame-Options set to 'DENY' in after_request [OK]

Hint: Headers set in @app.after_request apply to all responses [OK]

Common Mistakes:

• Assuming default header values without setting them
• Confusing SAMEORIGIN with DENY
• Thinking header is missing because not set in route

4. Identify the error in this Flask code that tries to add a Strict-Transport-Security header:

from flask import Flask
app = Flask(__name__)

@app.after_request
def secure_headers(response):
    response.headers['Strict-Transport-Security'] = 'max-age=31536000; includeSubDomains'
    return response

@app.route('/')
def index():
    return 'Welcome'

medium

A. The header name should be lowercase

B. No error; the code is correct

C. The header value string is missing quotes

D. The function must accept two parameters

Solution

1. Step 1: Review header name and value syntax

   Header names are case-insensitive; using 'Strict-Transport-Security' is valid. The value is a valid string with quotes.

2. Step 2: Check function signature and usage

   @app.after_request functions take one parameter (response) and return it. This matches the code.

3. Final Answer:

   No error; the code is correct -> Option B

4. Quick Check:

   Header added correctly in @app.after_request [OK]

Hint: Check function signature and header syntax carefully [OK]

Common Mistakes:

• Thinking header names must be lowercase
• Expecting two parameters in after_request function
• Missing quotes around header value string

5. You want to add multiple secure headers in Flask, but only for HTTPS requests. Which is the best way to do this securely and efficiently?

hard

A. Use @app.after_request to check request.is_secure and add headers conditionally

B. Add headers in each route function only if request.scheme == 'https'

C. Set headers globally without checking protocol, assuming HTTPS everywhere

D. Use @app.before_request to add headers before response is created

Solution

1. Step 1: Understand when headers should be added

   Secure headers like Strict-Transport-Security should only be sent over HTTPS to avoid security risks.

2. Step 2: Choose the best place to add headers conditionally

   @app.after_request runs after response creation and can access request.is_secure to conditionally add headers efficiently for all routes.

3. Step 3: Evaluate other options

   Adding headers in each route duplicates code; setting headers globally without checking protocol risks sending them over HTTP; @app.before_request cannot modify response headers.

4. Final Answer:

   Use @app.after_request to check request.is_secure and add headers conditionally -> Option A

5. Quick Check:

   Conditional header addition in @app.after_request is best [OK]

Hint: Check request.is_secure in @app.after_request [OK]

Common Mistakes:

• Adding headers in each route causing repetition
• Sending secure headers over HTTP by default
• Trying to set headers in @app.before_request which can't modify response