Common PHP security issues and solutions

1. SQL injection

SQL injection is one of the biggest threats to your website. If your database is injected by someone else’s SQL In the event of an attack, others can transfer your database, which may have more serious consequences.

Solution:

There are two mainstream solutions. Escape user-entered data or use encapsulated statements. The method of escaping is to encapsulate a function to filter the data submitted by the user and remove harmful tags. However, I don't recommend this method because it's easier to forget to do it everywhere.

Next, I will introduce how to use PDO to execute encapsulated statements (the same is true for mysqi):

$username = $_GET['username'];
 
$query = $pdo->prepare('SELECT * FROM users WHERE username = :username');
 
$query->execute(['username' => $username]);
 
$data = $query->fetch();

2, XSS

XSS is also called CSS (Cross Site Script), cross-site scripting attack. It refers to a malicious attacker inserting malicious html code into a Web page. When a user browses the page, the html code embedded in the Web will be executed, thereby achieving the special purpose of maliciously attacking the user.

Solution:

Do not trust any input from the user and filter out all special characters in the input. This will eliminate most XSS attacks:

<?php
 
$searchQuery = htmlentities($searchQuery, ENT_QUOTES);

Or you can use the template engine Twig. General template engines will add htmlentities to the output by default.

3. Run some operations.

Solution:

The most common defense method is to generate a CSRF token encrypted secure string, generally called Token, and store the Token in Cookie or Session.

Every time you construct a form on a web page, put the Token in the hidden field in the form. The form request server will then compare it based on the user's Cookie or the Token in the Session, and the verification will be successful. Give a pass.

Since the attacker cannot know the contents of the Token (the Token of each form is random), he cannot impersonate the user.

Recommended tutorial:

PHP video tutorial

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