PHP implements secure programming: practical attack and defense against hackers

With the continuous development and deepening of the Internet, various hacker attacks have occurred frequently, posing serious threats to network security. PHP is a commonly used web development language used by many businesses and developers to create websites and applications. Therefore, in PHP programming, how to implement safe programming has become very important.

This article will introduce common security vulnerabilities in the PHP language and how to prevent these vulnerabilities. At the same time, we will also share some hacker attack cases and corresponding countermeasures.

1. SQL injection

SQL injection is currently one of the most common web attack methods. Attackers take advantage of the SQL statement vulnerability in the input box and make the application execute malicious SQL code through some specific inputs, thereby obtaining and tampering with data.

How to prevent SQL injection?

① Use prepared statements

Use PDO or MySQLi extension in PHP to implement prepared statements. Prepared statements separate SQL statements and user input before execution, thereby avoiding user input injection attacks on SQL statements.

Sample code:

$stmt = $pdo->prepare('SELECT * FROM users WHERE username = :username');
$stmt->bindParam(':username', $username);
$stmt->execute();

② Filter input

At any time, do not trust the user’s input. Always filter user input. You can use the filter_input function in PHP or the developer writes his own filter function.

Sample code:

// 使用filter_input来避免SQL注入
$username = filter_input(INPUT_POST, 'username', FILTER_SANITIZE_SPECIAL_CHARS);

③ Restrict user input

Restricting input is a more stringent verification method that can prevent users from entering malicious SQL code. For example, you can stipulate that the username must not contain special characters or must be greater than or equal to 6 characters in length.

2. Cross-site scripting attack (XSS)

Cross-site scripting attack is an attack method against web applications. The attacker embeds script code in the website, and the user It is executed when visiting the website.

How to prevent XSS attacks?

① Filter user input

Just like preventing SQL injection, user input also needs to be filtered. For example, you can use the htmlspecialchars function to filter user input and convert special characters into HTML entities.

Sample code:

echo htmlspecialchars($_POST['message']);

② Mark the cookie as HTTP only

When setting a cookie, you can use the HTTP only tag. This will prevent JavaScript and other client-side scripts from accessing the cookie. If an attacker cannot access cookies, then they cannot use session hijacking attacks.

Sample code:

setcookie('session_id', $session_id, time() + 86400, '/', '', true, true);

3. File inclusion vulnerability

File inclusion vulnerability is a common web attack method. Attackers will use some means to manipulate the server file system to contain and run malicious code.

How to prevent file inclusion vulnerabilities?

① Use absolute paths

Relative paths are feasible under certain circumstances, but they may be exploited when limited tools are encountered or the directory structure changes. Use absolute paths to avoid this type of problem.

Sample code:

// 路径在Unix系统下
include '/var/www/html/includes/config.php';

② Limit file inclusion directories

Restricting the directories that can be included is one of the most direct and effective ways to achieve file inclusion security. Developers can hardcode the file paths that can be included in the application, or use the open_basedir option in the php.ini file to limit the accessible file paths.

4. CSRF attack

CSRF (Cross-Site Request Forgery) attack, also called cross-site request forgery attack, refers to an attacker using the identity of a logged-in user to An attack that performs certain actions without your knowledge.

How to prevent CSRF attacks?

① Verify the HTTP Referer header

The HTTP Referer header refers to the web page from which the user links to the target page. In CSRF attacks, attackers often fail to forge the correct HTTP Referer header. Therefore, developers can verify the HTTP Referer header to detect possible CSRF attacks.

Sample code:

// 从HTTP Referer头中获取URL
$referrer = parse_url($_SERVER['HTTP_REFERER']);
if ($referrer['host'] !== 'example.com')
{
    // 可能是CSRF攻击，拒绝请求
    die('CSRF detected!');
}

② Add CSRF token

CSRF token is an effective way to prevent CSRF attacks. On each form submission, generate a unique identifier that is included in the form data to prevent fake form submissions.

Sample code:

// 在表单中添加CSRF令牌
session_start();
$_SESSION['csrf_token'] = bin2hex(random_bytes(32));
echo '<input type="hidden" name="csrf_token" value="' . $_SESSION['csrf_token'] . '">';

When the attacker submits the form, it is necessary to verify whether the CSRF token is correct:

// 验证CSRF令牌是否正确
session_start();
if ($_POST['csrf_token'] !== $_SESSION['csrf_token'])
{
    // 可能是CSRF攻击，拒绝请求
    die('CSRF detected!');
}

5. Actual case of hacker attack and defense

Cases of hacker attacks are common. The following is a typical attack scenario:

After the attacker obtains the username and password, he tries to view the user list of the target website. The website is developed using PHP and uses MySQL database to store information. The attacker tried to use some basic SQL injection methods, and finally obtained the user list of the target website through the injection attack.

How to deal with this attack?

This attack can be prevented through the following measures:

① Strict verification of user input

As mentioned above, by filtering user input, restricting user input, using preset Processing statements and other methods can avoid SQL injection attacks.

② Strengthen access control

In order to ensure the security of user data, access control should be strengthened and appropriate permissions should be set. Only users with specific permissions can perform related operations, such as viewing the user list.

③ Encryption

Encryption can protect sensitive information, such as passwords, account information, etc. You should ensure that all sensitive information is encrypted when stored and transmitted.

Summarize

This article introduces common security vulnerabilities in PHP programming and how to prevent these vulnerabilities, including SQL injection, cross-site scripting attacks, file inclusion vulnerabilities, CSRF attacks, etc. In addition, we also analyzed a hacker attack case and provided corresponding countermeasures. Through these measures, developers can enhance the security of their applications and protect user data.

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