Plugin security (nonces, sanitization) in Wordpress - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a nonce field for security in a WordPress plugin form.

Wordpress

<?php wp_nonce_field([1], 'my_plugin_nonce'); ?>

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

A'my_plugin_action'

B'nonce_field'

C'my_plugin_nonce'

D'security_token'

Attempts:

3 left

💡 Hint

Common Mistakes

Using the nonce field name instead of the action name.

Leaving the first argument empty or incorrect.

The first argument to wp_nonce_field is the action name, which should be a unique string identifying the action.

2fill in blank

medium

Complete the code to verify the nonce in a WordPress plugin before processing form data.

Wordpress

if ( ! isset($_POST['my_plugin_nonce']) || ! wp_verify_nonce($_POST['my_plugin_nonce'], [1]) ) {
    die('Security check failed');
}

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

A'security_token'

B'my_plugin_nonce'

C'nonce_field'

D'my_plugin_action'

Attempts:

3 left

💡 Hint

Common Mistakes

Using the nonce field name instead of the action name.

Not checking if the nonce is set before verifying.

The second argument to wp_verify_nonce must match the action name used when creating the nonce.

3fill in blank

hard

Fix the error in sanitizing a text input from a form in a WordPress plugin.

Wordpress

$user_input = [1]($_POST['user_text']);

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

Asanitize_text_field

Besc_html

Cwp_kses_post

Dsanitize_email

Attempts:

3 left

💡 Hint

Common Mistakes

Using esc_html which is for output escaping, not input sanitization.

Using sanitize_email for non-email inputs.

sanitize_text_field is the correct function to clean plain text input from users.

4fill in blank

hard

Fill both blanks to safely output a sanitized user input in a WordPress plugin.

Wordpress

echo [1]( [2] );

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

Aesc_html

B$user_input

Csanitize_text_field

Dwp_kses_post

Attempts:

3 left

💡 Hint

Common Mistakes

Not escaping output before echoing.

Trying to sanitize again at output instead of escaping.

Use esc_html to safely display the sanitized user input stored in $user_input.

5fill in blank

hard

Fill all three blanks to create a secure form handler in a WordPress plugin.

Wordpress

if ( isset($_POST['submit']) && wp_verify_nonce($_POST['[1]'], '[2]') ) {
    $safe_input = [3]($_POST['user_input']);
    // Process $safe_input
}

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

Amy_plugin_nonce

Bmy_plugin_action

Csanitize_text_field

Desc_html

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up nonce field name and action name.

Not sanitizing input before use.

Verify the nonce field 'my_plugin_nonce' with action 'my_plugin_action' and sanitize input with sanitize_text_field.

Practice

1. What is the main purpose of using a nonce in a WordPress plugin?

easy

A. To speed up the plugin loading time

B. To protect against unauthorized or fake form submissions

C. To style the plugin interface

D. To store user preferences permanently

Solution

1. Step 1: Understand what a nonce is

   A nonce is a unique token used to verify that a request comes from a trusted source.

2. Step 2: Identify nonce purpose in plugins

   Nonces prevent attackers from submitting fake or unauthorized requests to your plugin.

3. Final Answer:

   To protect against unauthorized or fake form submissions -> Option B

4. Quick Check:

   Nonce = Security token for requests [OK]

Hint: Nonces stop fake requests, like a secret handshake [OK]

Common Mistakes:

• Thinking nonce speeds up plugin
• Using nonce for styling
• Confusing nonce with data storage

2. Which of the following is the correct way to check a nonce in a WordPress plugin?

easy

A. check_nonce('my_nonce')

B. nonce_check('my_nonce')

C. wp_verify_nonce($_POST['my_nonce'], 'my_action')

D. verify_nonce('my_nonce')

Solution

1. Step 1: Recall the WordPress function for nonce verification

   The correct function to verify a nonce is wp_verify_nonce().

2. Step 2: Check the correct usage

   The function takes the nonce value and the action name as parameters, like wp_verify_nonce($_POST['my_nonce'], 'my_action').

3. Final Answer:

   wp_verify_nonce($_POST['my_nonce'], 'my_action') -> Option C

4. Quick Check:

   Verify nonce = wp_verify_nonce() [OK]

Hint: Use wp_verify_nonce() with nonce and action [OK]

Common Mistakes:

• Using non-existent functions like check_nonce
• Passing wrong parameters order
• Not using $_POST or $_GET to get nonce

3. What will be the output of this code snippet in a WordPress plugin?

if ( ! wp_verify_nonce($_POST['nonce'], 'save_data') ) {
  echo 'Invalid nonce';
} else {
  $name = sanitize_text_field($_POST['name']);
  echo 'Hello, ' . $name;
}

Assuming the nonce is valid and $_POST['name'] = '<script>alert(1)</script>John'?

medium

A. Hello, John

B. Hello, John

C. Invalid nonce

D. Hello, alert(1)John

Solution

1. Step 1: Check nonce validity

   The nonce is valid, so the else block runs.

2. Step 2: Understand sanitize_text_field effect

   This function removes HTML tags like <script>, so the input becomes 'alert(1)John' because sanitize_text_field removes tags but leaves the text inside.

3. Step 3: Clarify output

   The output will be 'Hello, alert(1)John' because the script tags are stripped but the text 'alert(1)' remains.

4. Final Answer:

   Hello, alert(1)John -> Option D

5. Quick Check:

   Sanitize removes tags but keeps text inside [OK]

Hint: sanitize_text_field strips HTML tags but keeps inner text [OK]

Common Mistakes:

• Assuming sanitize_text_field allows HTML
• Ignoring nonce check result
• Confusing output with raw input

4. Identify the error in this WordPress plugin code snippet:

if ( ! wp_verify_nonce($_POST['nonce'], 'save_data') ) {
  wp_die('Security check failed');
}
$name = sanitize_text_field($_POST['name']);
update_option('user_name', $name);

medium

A. Not checking if $_POST['name'] is set before sanitizing

B. Missing nonce field in the form

C. Using update_option instead of add_option

D. No error, code is correct

Solution

1. Step 1: Check nonce verification

   The nonce is verified correctly with wp_verify_nonce and wp_die on failure.

2. Step 2: Check input sanitization safety

   The code sanitizes $_POST['name'] without checking if it exists, which can cause a PHP notice or error.

3. Final Answer:

   Not checking if $_POST['name'] is set before sanitizing -> Option A

4. Quick Check:

   Always check input exists before sanitizing [OK]

Hint: Check if input exists before sanitize_text_field [OK]

Common Mistakes:

• Assuming update_option is wrong here
• Ignoring missing input checks
• Thinking nonce check is missing

5. You want to securely save a user email from a form in your WordPress plugin. Which combination of code snippets correctly uses nonce verification and sanitization?

// 1. Verify nonce
if ( ! wp_verify_nonce($_POST['nonce'], 'save_email') ) {
  wp_die('Invalid request');
}

// 2. Sanitize input
$email = ???

// 3. Save email
update_option('user_email', $email);

Choose the correct code for step 2:

hard

A. $email = sanitize_email($_POST['email']);

B. $email = sanitize_text_field($_POST['email']);

C. $email = esc_html($_POST['email']);

D. $email = wp_strip_all_tags($_POST['email']);

Solution

1. Step 1: Confirm nonce verification

   The nonce is verified correctly before processing input.

2. Step 2: Choose proper sanitization for email

   For emails, sanitize_email() is the correct function to clean and validate email format.

3. Step 3: Understand other options

   sanitize_text_field() is for plain text, esc_html() is for output escaping, and wp_strip_all_tags() removes tags but does not validate email.

4. Final Answer:

   $email = sanitize_email($_POST['email']); -> Option A

5. Quick Check:

   Email input = sanitize_email() [OK]

Hint: Use sanitize_email() for email inputs [OK]

Common Mistakes:

• Using sanitize_text_field for emails
• Confusing escaping with sanitizing
• Not verifying nonce before saving