How to Avoid SQL Injection When Using `bindValue` in a LIMIT Clause?

How to Prevent SQL Injection When Using BindValue in LIMIT Clause

When attempting to execute an SQL query using the bindValue method to parametrize the LIMIT clause, PHP PDO may add single quotes to the variable values. This behavior can lead to SQL syntax errors as observed in the provided code snippet:

$fetchPictures->prepare("SELECT * 
    FROM pictures 
    WHERE album = :albumId 
    ORDER BY id ASC 
    LIMIT :skip, :max");

$fetchPictures->bindValue(':albumId', $_GET['albumid'], PDO::PARAM_INT);

if(isset($_GET['skip'])) {
    $fetchPictures->bindValue(':skip', trim($_GET['skip']), PDO::PARAM_INT);    
} else {
    $fetchPictures->bindValue(':skip', 0, PDO::PARAM_INT);  
}

$fetchPictures->bindValue(':max', $max, PDO::PARAM_INT);
$fetchPictures->execute() or die(print_r($fetchPictures->errorInfo()));
$pictures = $fetchPictures->fetchAll(PDO::FETCH_ASSOC);

The error message "You have an error in your SQL syntax" is likely caused by single quotes being added to the :skip variable in the LIMIT clause.

It is believed that this behavior is related to a long-standing bug in PDO reported in 2008: https://bugs.php.net/bug.php?id=44639

Solution:

As suggested in the response, casting the values to integers before passing them to the bindValue method solves this issue:

$fetchPictures->bindValue(':skip', (int) trim($_GET['skip']), PDO::PARAM_INT);

By converting the $_GET['skip'] variable to an integer using (int) before binding, we prevent PDO from adding single quotes and ensure that the SQL query is executed correctly.

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