Secure coding is not just "not making mistakes". It is an entire philosophy: not trusting any user input, checking every external source, and properly formatting every output. Experienced developers call this "defense in depth" — meaning protection should exist at every layer. If one layer fails, the second one protects. This approach is especially important in web applications because they are constantly open to attacks through the internet.
SQL injection — the most dangerous vulnerability
SQL injection is when an attacker gains the ability to control the database by adding their commands to an SQL query. For example, if you directly insert a user-entered ID into SQL, the attacker can write "1 OR 1=1" instead of an ID and read the entire table. Or write "1; DROP TABLE users" and completely delete the table. The only correct way to protect is to use prepared statements. In PDO or MySQLi prepared statements, data does not mix with SQL code and the attack possibility disappears.
XSS — Cross-Site Scripting attack
An XSS attack is the injection of foreign JavaScript code into a page. If you output text entered by a user directly into an HTML page, the attacker can steal session cookies through a script tag, redirect the user to another site, or perform actions on their behalf. Protection is very simple: before output, you need to use the htmlspecialchars() function with the ENT_QUOTES flag. Additionally, the Content Security Policy header provides another layer of protection.
CSRF — Cross-Site Request Forgery
In a CSRF attack, a user performs an action on another site without knowing it. For example, a user logged into your site and their session is open. Then they go to another site where there is a hidden form sending a request to your site — the browser automatically adds cookies and the request is executed. Protection is using a unique CSRF token in each form. This token is stored in the session and verified on the server.
Secure defaults
A good program should be written so that even if the developer makes no settings, the system is still in a safe state. For example, a new user should not automatically get admin rights. A new file should not be automatically open to everyone. Cookies should automatically be HttpOnly and Secure. The session should automatically regenerate. This principle is called "secure by default" and is applied as a standard in modern frameworks.
Sayt.uz practice
On the Sayt.uz platform, all SQL queries are executed through PDO prepared statements. User inputs are filtered with htmlspecialchars(), and Content Security Policy headers are activated. Every important form is protected with a CSRF token. If you host your site on Sayt.uz hosting, server-level protection layers provide additional security.