Description:
------------
---
From manual page: https://php.net/pdo.quote
---

Running PDO::quote() on a string which ends in a quote (e.g. Naughty ' string') will result in a string which ends in an escaped quote (e.g. 'Naughty \' string\'). This opens a door to SQL injection; see the vulnerability example in the 'Test script' box, below.

Test script:
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$name = '; DROP TABLE `test_table`; --\'';

// Sample PDO connection; can be whatever
$conn = new PDO('sqlite:/home/lynn/music.sql3');

$query = "SELECT * FROM `students` WHERE `first_name` = '%s' OR `last_name` = '%s'";
$query = sprintf($query, $conn->quote($name), $conn->quote($name));

echo $query;


Expected result:
----------------
I'm expecting the PHP script to echo the following string:
SELECT * FROM `students` WHERE `first_name` = '; DROP TABLE `test_table`; --\'' OR `last_name` = '; DROP TABLE `test_table`; --\''

However, as seen in the 'Actual result' box, it's missing the end quote each time $name was inserted into the query string. This happens because PDO::quote() doesn't add the end quote if the original string already ends in a quote, as explained in the 'Description' box.

Actual result:
--------------
The script will echo:
SELECT * FROM `students` WHERE `first_name` = '; DROP TABLE `test_table`; --\' OR `last_name` = '; DROP TABLE `test_table`; --\'

The above is basically two MySQL queries:
1. SELECT * FROM `students` WHERE `first_name` = '; DROP TABLE `test_table`; --\' OR `last_name` = ';
2. DROP TABLE `test_table`; // dangerous