PHP study notes: security and defense measures

PHP Study Notes: Security and Defense Measures

Introduction:
In today's Internet world, security is very important, especially for the Web application. As a commonly used server-side scripting language, PHP security has always been an aspect that developers must pay attention to. This article will introduce some common security issues in PHP and provide sample code for some defensive measures.

1. Input verification
Input verification is the first line of defense to protect the security of web applications. In PHP, we usually use filtering and validation techniques to ensure that the data entered by users is legal and safe.

1. Process input data through filtering and validation functions, such as using the filter_var() function:
   Code example:

   $username = filter_var($_POST['username'], FILTER_SANITIZE_STRING);
   $email = filter_var($_POST['email'], FILTER_VALIDATE_EMAIL);

2. Pair Strict restrictions on user input, such as specifying the length range of usernames and passwords:
   Code example:

   if (strlen($username) < 6 || strlen($username) > 20) {
   echo "用户名长度必须在6到20之间";
   }

2. XSS attack defense
Cross-site scripting attack (XSS) Is a common attack method that exploits a web application's improper processing of user input data to execute malicious scripts on the user's browser. The following are several ways to defend against XSS attacks:

1. Use the htmlspecialchars() function to escape the output:
   Code example:

   echo htmlspecialchars($userInput, ENT_QUOTES, 'UTF-8');

2. Use Content Security Policy (CSP) to limit the loading of external resources and prevent the injection of malicious scripts:
   Code example:

   header("Content-Security-Policy: script-src 'self'");

3. SQL injection defense
SQL Injection refers to an attacker tampering with database query statements through maliciously constructed character sequences to perform malicious operations on web applications. The following are several ways to defend against SQL injection:

1. Use prepared statements (Prepared Statements) to bind parameters:
   Code example:

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

2. Use PDO's quote() function to escape parameters:
   Code example:

   $username = $pdo->quote($_POST['username']);
   $query = "SELECT * FROM users WHERE username = $username";

4. File upload security
The file upload function is a Web application Common functions in the program. However, malicious users may upload files containing malicious scripts. The following are several methods to prevent file upload security issues:

1. Verify the suffix name of the uploaded file:
   Code example:

   $allowedExtensions = ['jpg', 'png', 'gif'];
   $filename = $_FILES['file']['name'];
   $ext = pathinfo($filename, PATHINFO_EXTENSION);
   if (!in_array($ext, $allowedExtensions)) {
    echo "文件类型不允许";
   }

2. Save uploaded files in an isolated directory to avoid direct access to files uploaded by users:
   Code example:

   $filename = uniqid().'.'.$ext;
   move_uploaded_file($_FILES['file']['tmp_name'], 'uploads/'.$filename);

5. Session management security
Session management It is an important component in web applications. The following are several session management security measures:

1. Store the session id in the HttpOnly cookie to avoid being obtained by malicious scripts:
   Code example:

   session_set_cookie_params(['httponly' => true]);
   session_start();

2. Regularly update the session id to avoid session hijacking:
   Code sample:

   session_start();
   if (isset($_SESSION['LAST_ACTIVITY']) && (time() - $_SESSION['LAST_ACTIVITY'] > 3600)) {
     session_regenerate_id(true);
   }
   $_SESSION['LAST_ACTIVITY'] = time();

Summary:
Through the several security issues mentioned above and defensive measures, we can strengthen the security of PHP web applications. However, security is an ongoing process, and developers should continue to learn and update their knowledge to respond to evolving and changing security threats. At the same time, you should also pay attention to the security best practice recommendations in the official PHP documentation to improve the security of your web applications.

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