With the popularity and development of web applications, network attacks have become a serious problem. Among them, CSRF (Cross-Site Request Forgery) attack is a very common attack method. Attackers can use this vulnerability to trick users into performing malicious operations, such as malicious transfers, modifying user information, etc. In order to improve the security of the application, we must take measures to protect the web application, one of which is the CSRF protection mechanism. This article will introduce the CSRF protection mechanism in Spring Security and provide some examples and practical suggestions to help developers implement more secure web applications.
CSRF attack
The essence of a CSRF attack is that the attacker performs malicious operations as a user. The attacker creates a page with malicious code, and the website user performs a request on the page. This request may modify the user account status, log out the user, etc. When a user accesses a normal website through a logged-in state, the request for this attack is automatically executed. Although the attack does not directly obtain the user's personal information, the consequences of data loss are dire.
Let's say you have an application that contains a page to modify your profile:
<form action="http://bank.com/withdraw.asp" method="post">
<input type="hidden" name="account" value="myaccount" />
<input type="hidden" name="amount" value="1000000" />
<input type="submit" value="转账" />
</form>
An attacker can create an email with malicious code that automatically launches the attack when a user opens the email. The attack code might look like this:
<img src="http://yourbank.com/withdraw.asp?account=myaccount&amount=1000000">
This type of attack will cause users to perform undesirable actions on the website rather than the actions they intended.
CSRF protection mechanism
To protect web applications from CSRF attacks, we can use the CSRF protection mechanism provided by Spring Security. It works by adding a CSRF token to the request form, which is generated on the client side and then verified on the server side. Spring Security provides the following three methods for CSRF protection:
Synchronizer Token Pattern
Synchronizer Token Pattern is the most common CSRF protection method. The workflow is as follows:
- The server generates a random token for the user and adds it to the form
- When the user submits the form, the random token will be submitted to the server together.
- The server verifies whether the token is consistent with what the user submitted
- If they are consistent, the request will be allowed; if they are inconsistent, the request will be rejected.
Here is an example of a form containing a randomly generated token:
<form method="post">
<input type="hidden" name="csrf_token" value="mGa7b5YnWNJBK8R8WdXsjSBBH7mC4sDv">
<input type="text" name="text_field">
<input type="submit" name="submit">
</form>
Double Submit Cookie Pattern
Double Submit Cookie Pattern is another common CSRF protection mechanism. The workflow is as follows:
- When a user accesses a web application, the server creates a randomly generated token and saves it as a cookie
- When the user sends a request to the server, the form and a cookie containing the token are submitted to the server.
- The server verifies whether the submitted cookie is consistent with the token in the form
- If the cookie and token are consistent, the request will be allowed, otherwise the request will be rejected.
Here is an example of a form and a token stored in a cookie:
<form method="post">
<input type="text" name="text_field">
<input type="submit" name="submit">
</form>
When the Double Submit Cookie Pattern is enabled, Spring Security will automatically verify that the cookie and the token in the form in the request are consistent.
Custom CSRF Filter
Custom CSRF Filter allows us to customize the CSRF protection mechanism. This mechanism uses AOP (Aspect-Oriented Programming) to control CSRF attacks by processing pre- and post-notifications. We can write a custom filter to modify the request form for cross-site scripting language attacks, verify CSRF tokens, or any other custom logic.
@Bean
public CSRFFilter csrfFilter() {
CSRFFilter filter = new CSRFFilter();
return filter;
}
In this example, we create a bean called csrffilter and enable our custom CSRF protection mechanism through it.
All three methods above can protect web applications from CSRF attacks, and we can choose according to specific application needs.
CSRF protection implementation example
Implementing CSRF protection in Spring Security is very simple, we only need to enable CSRF protection in the configuration file and add the CSRF token in the form.
1. Enable CSRF protection in Spring Security
To enable CSRF protection in Spring Security, we need to set csrf() in the Spring Security configuration as follows:
@Configuration
@EnableWebSecurity
public class WebSecurityConfig extends WebSecurityConfigurerAdapter {
@Override
protected void configure(HttpSecurity http) throws Exception {
http.csrf();
}
}
In this example, we enable CSRF protection in Spring Security and apply it to the http configuration.
2. Add CSRF token to the form
Adding a CSRF token to a form is very simple, you can use the CSRF tag in Spring Security, as shown below:
<form action="/submit" method="post">
<!--A CSRF token to prevent CSRF attacks-->
<input type="hidden" name="${_csrf.parameterName}" value="${_csrf.token}" />
<input type="text" name="text_field" />
<input type="submit" name="submit" value="Submit" />
</form>
In this example, we use the _csrf parameter name and the token value of _csrf in Spring Security to add a CSRF token. When the form is submitted, Spring Security automatically checks the token to ensure that the form request is valid and has not been tampered with.
in conclusion
This article introduces the principles of CSRF attacks, threats to web applications, and methods of using the CSRF protection mechanism in Spring Security to protect web applications. We learned about three different CSRF protection mechanisms in Spring Security, namely synchronizer token mode, double-submit cookie mode and custom CSRF filter. For high-security web applications, these mechanisms are essential and should be applied appropriately in the implementation of the program.