SQL injection prevention in Wordpress - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to safely prepare a SQL query using WordPress functions.

Wordpress

$wpdb->prepare("SELECT * FROM wp_users WHERE ID = [1]", $user_id);

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

A%x

B%d

C%s

D%f

Attempts:

3 left

💡 Hint

Common Mistakes

Using %s for integers causes errors or unsafe queries.

Not using prepare() leads to SQL injection risks.

Use %d to safely insert an integer value in the query.

2fill in blank

medium

Complete the code to safely insert a string value into the database using WordPress.

Wordpress

$wpdb->prepare("SELECT * FROM wp_posts WHERE post_title = [1]", $title);

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

A%x

B%f

C%d

D%s

Attempts:

3 left

💡 Hint

Common Mistakes

Using %d for strings causes errors or unsafe queries.

Not using prepare() leads to SQL injection risks.

Use %s to safely insert a string value in the query.

3fill in blank

hard

Fix the error in the code to prevent SQL injection by using the correct WordPress function.

Wordpress

$wpdb->query([1]);

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

A$user_login

B$wpdb->escape($user_login)

C$wpdb->prepare("SELECT * FROM wp_users WHERE user_login = %s", $user_login)

D$wpdb->prepare($user_login)

Attempts:

3 left

💡 Hint

Common Mistakes

Using variables directly in the query string.

Using deprecated or incorrect escaping functions.

Use $wpdb->prepare("SELECT * FROM wp_users WHERE user_login = %s", $user_login) to safely insert the string and prevent SQL injection.

4fill in blank

hard

Fill both blanks to safely update a post title using WordPress functions.

Wordpress

$wpdb->query($wpdb->prepare("UPDATE wp_posts SET post_title = [1] WHERE ID = [2]", $new_title, $post_id));

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

A%s

B%d

C%f

D%x

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up placeholders causes errors or unsafe queries.

Not using prepare() leads to SQL injection risks.

Use %s for the string title and %d for the integer post ID.

5fill in blank

hard

Fill both blanks to safely select posts with a minimum comment count using WordPress prepare.

Wordpress

$wpdb->get_results($wpdb->prepare("SELECT * FROM wp_posts WHERE comment_count [1] [2]", $min_comment_count));

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

A>

B>=

C%d

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong comparison operators.

Not using placeholders for variables.

Use >= to select posts with comment count greater or equal, and %d as the placeholder for the integer value.

Practice

1. What is the main purpose of using $wpdb->prepare() in WordPress?

easy

A. To speed up database queries by caching results

B. To safely insert user input into SQL queries and prevent SQL injection

C. To format dates and times in SQL queries

D. To automatically backup the database before running queries

Solution

1. Step 1: Understand the role of $wpdb->prepare()

   $wpdb->prepare() is designed to safely insert user data into SQL queries by escaping dangerous characters.

2. Step 2: Identify the security benefit

   This prevents attackers from injecting harmful SQL commands that could damage or expose the database.

3. Final Answer:

   To safely insert user input into SQL queries and prevent SQL injection -> Option B

4. Quick Check:

   SQL injection prevention = B [OK]

Hint: Remember: prepare() protects queries from harmful input [OK]

Common Mistakes:

• Thinking prepare() speeds up queries
• Confusing prepare() with formatting dates
• Assuming prepare() backs up the database

2. Which of the following is the correct syntax to prepare a SQL query with one string placeholder in WordPress?

easy

A. $wpdb->prepare('SELECT * FROM wp_users WHERE user_login = %s', $username);

B. $wpdb->prepare('SELECT * FROM wp_users WHERE user_login = ?', $username);

C. $wpdb->prepare('SELECT * FROM wp_users WHERE user_login = :username', $username);

D. $wpdb->prepare('SELECT * FROM wp_users WHERE user_login = $username');

Solution

1. Step 1: Identify correct placeholder syntax

   WordPress uses %s for string placeholders in $wpdb->prepare(), not ? or named placeholders.

2. Step 2: Match the placeholder with the variable

   The variable $username is passed as the second argument to safely replace %s.

3. Final Answer:

   $wpdb->prepare('SELECT * FROM wp_users WHERE user_login = %s', $username); -> Option A

4. Quick Check:

   Use %s for strings in prepare() = A [OK]

Hint: Use %s for strings, %d for numbers in prepare() [OK]

Common Mistakes:

• Using ? instead of %s as placeholder
• Using named placeholders like :username
• Not passing variables as arguments to prepare()

3. What will be the output of the following code snippet?

$user_id = 5;
$query = $wpdb->prepare('SELECT * FROM wp_users WHERE ID = %d', $user_id);
echo $query;

medium

A. SELECT * FROM wp_users WHERE ID = 5

B. SELECT * FROM wp_users WHERE ID = %d

C. SELECT * FROM wp_users WHERE ID = '5'

D. Error: Missing argument for prepare()

Solution

1. Step 1: Understand %d placeholder usage

   %d is used for integers and will be replaced by the integer value without quotes.

2. Step 2: Check the variable substitution

   $user_id = 5 replaces %d, so the query becomes SELECT * FROM wp_users WHERE ID = 5.

3. Final Answer:

   SELECT * FROM wp_users WHERE ID = 5 -> Option A

4. Quick Check:

   Integer placeholder %d replaced by 5 = A [OK]

Hint: Integer placeholders %d insert numbers without quotes [OK]

Common Mistakes:

• Expecting %d to be replaced with quoted '5'
• Thinking prepare() returns an error without extra arguments
• Confusing %d with %s for strings

4. Identify the error in this WordPress SQL preparation code:

$email = $_POST['email'];
$query = $wpdb->prepare('SELECT * FROM wp_users WHERE user_email = %d', $email);

medium

A. Missing the global $wpdb declaration

B. Not sanitizing the $_POST input before prepare()

C. Using %d placeholder for an email string instead of %s

D. prepare() cannot be used with SELECT queries

Solution

1. Step 1: Check placeholder type vs variable type

   %d is for integers, but $email is a string, so %s should be used.

2. Step 2: Understand prepare() placeholder matching

   Using wrong placeholder causes SQL errors or unexpected behavior.

3. Final Answer:

   Using %d placeholder for an email string instead of %s -> Option C

4. Quick Check:

   Placeholder type must match variable type = C [OK]

Hint: Match %s for strings, %d for numbers in prepare() [OK]

Common Mistakes:

• Using %d for strings like emails
• Assuming prepare() sanitizes input fully
• Thinking prepare() can't be used with SELECT

5. You want to safely query posts by author ID and post status using $wpdb->prepare(). Which of the following is the best way to write this query?

hard

A. $wpdb->prepare('SELECT * FROM wp_posts WHERE post_author = ? AND post_status = ?', $author_id, $status);

B. $wpdb->prepare('SELECT * FROM wp_posts WHERE post_author = %s AND post_status = %d', $author_id, $status);

C. $wpdb->prepare('SELECT * FROM wp_posts WHERE post_author = $author_id AND post_status = '$status'');

D. $wpdb->prepare('SELECT * FROM wp_posts WHERE post_author = %d AND post_status = %s', $author_id, $status);

Solution

1. Step 1: Match placeholders to variable types

   $author_id is a number, so use %d; $status is a string, so use %s.

2. Step 2: Verify correct usage of prepare()

   $wpdb->prepare('SELECT * FROM wp_posts WHERE post_author = %d AND post_status = %s', $author_id, $status); correctly uses %d and %s placeholders with variables passed as arguments.

3. Step 3: Identify errors in other options

   Using ? placeholders is unsupported; using %s for post_author (integer) and %d for post_status (string) mismatches types; directly inserting variables into the query string is unsafe.

4. Final Answer:

   $wpdb->prepare('SELECT * FROM wp_posts WHERE post_author = %d AND post_status = %s', $author_id, $status); -> Option D

5. Quick Check:

   %d for author_id, %s for status = D [OK]

Hint: Use %d for numbers, %s for strings in prepare() [OK]

Common Mistakes:

• Swapping %d and %s placeholders
• Using ? instead of % placeholders
• Injecting variables directly into query string