PHP study notes: Web security and vulnerability prevention

PHP study notes: Web security and vulnerability prevention

Introduction:
In the field of Web development, security has always been an important topic. With the rapid development of the Internet, various network attacks and vulnerabilities are constantly emerging. Therefore, it is very important for developers to learn and master relevant security knowledge and preventive measures. This article will focus on web security issues in PHP and how to prevent some common vulnerabilities, and give specific code examples.

1. SQL injection attack
SQL injection is one of the most common security vulnerabilities in web applications. It constructs malicious SQL statements to obtain sensitive information in the database or modify database contents. The most important way to protect against SQL injection is to use parameterized queries or prepared statements to process user-entered data.

Sample code:

// 使用参数化查询方式防止SQL注入
$username = $_POST['username'];
$password = $_POST['password'];

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

// 预编译语句防止SQL注入
$username = $_POST['username'];
$password = $_POST['password'];

$stmt = $pdo->prepare("SELECT * FROM users WHERE username = ? AND password = ?");
$stmt->execute([$username, $password]);

2. Cross-site scripting attack (XSS)
XSS is an attack method that exploits website vulnerabilities. The attacker injects JavaScript code into the web page, thereby Obtain the user's sensitive information or hijack the user's session. Methods to prevent XSS attacks include filtering and escaping user input, and setting the HttpOnly attribute to restrict JavaScript's access to cookies.

Sample code:

// 对用户输入进行过滤和转义
$input = $_GET['input'];
$filtered_input = htmlspecialchars($input);

echo "您输入的内容是：" . $filtered_input;

// 设置HttpOnly属性来限制JavaScript对Cookie的访问
setcookie('session_id', $session_id, time() + 3600, '/', '', true, true);

3. Cross-site request forgery (CSRF)
CSRF attack is an attack method that uses the identity of a trusted user to perform illegal operations. Methods to prevent CSRF include using random tokens to verify user identities and secondary confirmation of sensitive operations.

Sample code:

// 使用随机令牌验证用户身份
$token = md5(uniqid(rand(), true));
$_SESSION['token'] = $token;

// 在表单中加入隐藏字段
<input type="hidden" name="token" value="<?php echo $_SESSION['token']; ?>">

// 在处理请求时验证令牌
if ($_POST['token'] === $_SESSION['token']) {
    // 执行敏感操作
}

// 对敏感操作进行二次确认
if ($_POST['confirm'] === 'yes') {
    // 执行敏感操作
}

Conclusion:
Web security is a large and complex field, and this article only briefly introduces part of it. In the actual development process, we also need to continuously learn and understand new security threats and preventive measures to ensure the security of web applications. I hope this article can be helpful to PHP learners about web security.

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