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Cross Site Request Forgery (CSRF) for Servlet Environments

This section discusses Spring Security’s Cross Site Request Forgery (CSRF) support for servlet environments.

Using Spring Security CSRF Protection

The steps to using Spring Security’s CSRF protection are outlined below:

Use proper HTTP verbs
Configure CSRF Protection
Include the CSRF Token

Use proper HTTP verbs

The first step to protecting against CSRF attacks is to ensure your website uses proper HTTP verbs. This is covered in detail in Safe Methods Must be Idempotent.

Configure CSRF Protection

The next step is to configure Spring Security’s CSRF protection within your application. Spring Security’s CSRF protection is enabled by default, but you may need to customize the configuration. Below are a few common customizations.

Custom CsrfTokenRepository

By default Spring Security stores the expected CSRF token in the HttpSession using HttpSessionCsrfTokenRepository. There can be cases where users will want to configure a custom CsrfTokenRepository. For example, it might be desirable to persist the CsrfToken in a cookie to support a JavaScript based application.

By default the CookieCsrfTokenRepository will write to a cookie named XSRF-TOKEN and read it from a header named X-XSRF-TOKEN or the HTTP parameter _csrf. These defaults come from AngularJS

You can configure CookieCsrfTokenRepository in XML using the following:

Store CSRF Token in a Cookie with XML Configuration

<http>
	<!-- ... -->
	<csrf token-repository-ref="tokenRepository"/>
</http>
<b:bean id="tokenRepository"
	class="org.springframework.security.web.csrf.CookieCsrfTokenRepository"
	p:cookieHttpOnly="false"/>

The sample explicitly sets cookieHttpOnly=false. This is necessary to allow JavaScript (i.e. AngularJS) to read it. If you do not need the ability to read the cookie with JavaScript directly, it is recommended to omit cookieHttpOnly=false to improve security.

You can configure CookieCsrfTokenRepository in Java Configuration using:

Store CSRF Token in a Cookie

Java
Kotlin

@EnableWebSecurity
public class WebSecurityConfig {

	@Bean
	public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
		http
			.csrf(csrf -> csrf
				.csrfTokenRepository(CookieCsrfTokenRepository.withHttpOnlyFalse())
			);
		return http.build();
	}
}

@EnableWebSecurity
class SecurityConfig {

    @Bean
    open fun filterChain(http: HttpSecurity): SecurityFilterChain {
       http {
            csrf {
                csrfTokenRepository = CookieCsrfTokenRepository.withHttpOnlyFalse()
            }
        }
        return http.build()
    }
}

Disable CSRF Protection

CSRF protection is enabled by default. However, it is simple to disable CSRF protection if it makes sense for your application.

The XML configuration below will disable CSRF protection.

Disable CSRF XML Configuration

<http>
	<!-- ... -->
	<csrf disabled="true"/>
</http>

The Java configuration below will disable CSRF protection.

Disable CSRF

Java
Kotlin

@Configuration
@EnableWebSecurity
public class WebSecurityConfig {

	@Bean
	public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
		http
			.csrf(csrf -> csrf.disable());
		return http.build();
	}
}

@Configuration
@EnableWebSecurity
class SecurityConfig {

    @Bean
    open fun filterChain(http: HttpSecurity): SecurityFilterChain {
       http {
            csrf {
                disable()
            }
        }
        return http.build()
    }
}

Include the CSRF Token

In order for the synchronizer token pattern to protect against CSRF attacks, we must include the actual CSRF token in the HTTP request. This must be included in a part of the request (i.e. form parameter, HTTP header, etc) that is not automatically included in the HTTP request by the browser.

Spring Security’s CsrfFilter exposes a CsrfToken as an HttpServletRequest attribute named _csrf. This means that any view technology can access the CsrfToken to expose the expected token as either a form or meta tag. Fortunately, there are integrations listed below that make including the token in form and ajax requests even easier.

Form URL Encoded

In order to post an HTML form the CSRF token must be included in the form as a hidden input. For example, the rendered HTML might look like:

CSRF Token HTML

<input type="hidden"
	name="_csrf"
	value="4bfd1575-3ad1-4d21-96c7-4ef2d9f86721"/>

Next we will discuss various ways of including the CSRF token in a form as a hidden input.

Automatic CSRF Token Inclusion

Spring Security’s CSRF support provides integration with Spring’s RequestDataValueProcessor via its CsrfRequestDataValueProcessor. This means that if you leverage Spring’s form tag library, Thymeleaf, or any other view technology that integrates with RequestDataValueProcessor, then forms that have an unsafe HTTP method (i.e. post) will automatically include the actual CSRF token.

csrfInput Tag

If you are using JSPs, then you can use Spring’s form tag library. However, if that is not an option, you can also easily include the token with the csrfInput tag.

CsrfToken Request Attribute

If the other options for including the actual CSRF token in the request do not work, you can take advantage of the fact that the CsrfToken is exposed as an HttpServletRequest attribute named _csrf.

An example of doing this with a JSP is shown below:

CSRF Token in Form with Request Attribute

<c:url var="logoutUrl" value="/logout"/>
<form action="${logoutUrl}"
	method="post">
<input type="submit"
	value="Log out" />
<input type="hidden"
	name="${_csrf.parameterName}"
	value="${_csrf.token}"/>
</form>

Ajax and JSON Requests

If you are using JSON, then it is not possible to submit the CSRF token within an HTTP parameter. Instead you can submit the token within a HTTP header.

In the following sections we will discuss various ways of including the CSRF token as an HTTP request header in JavaScript based applications.

Automatic Inclusion

Spring Security can easily be configured to store the expected CSRF token in a cookie. By storing the expected CSRF in a cookie, JavaScript frameworks like AngularJS will automatically include the actual CSRF token in the HTTP request headers.

Meta tags

An alternative pattern to exposing the CSRF in a cookie is to include the CSRF token within your meta tags. The HTML might look something like this:

CSRF meta tag HTML

<html>
<head>
	<meta name="_csrf" content="4bfd1575-3ad1-4d21-96c7-4ef2d9f86721"/>
	<meta name="_csrf_header" content="X-CSRF-TOKEN"/>
	<!-- ... -->
</head>
<!-- ... -->

Once the meta tags contained the CSRF token, the JavaScript code would read the meta tags and include the CSRF token as a header. If you were using jQuery, this could be done with the following:

AJAX send CSRF Token

$(function () {
	var token = $("meta[name='_csrf']").attr("content");
	var header = $("meta[name='_csrf_header']").attr("content");
	$(document).ajaxSend(function(e, xhr, options) {
		xhr.setRequestHeader(header, token);
	});
});

csrfMeta tag

If you are using JSPs a simple way to write the CSRF token to the meta tags is by leveraging the csrfMeta tag.

CsrfToken Request Attribute

CSRF meta tag JSP

<html>
<head>
	<meta name="_csrf" content="${_csrf.token}"/>
	<!-- default header name is X-CSRF-TOKEN -->
	<meta name="_csrf_header" content="${_csrf.headerName}"/>
	<!-- ... -->
</head>
<!-- ... -->

CSRF Considerations

There are a few special considerations to consider when implementing protection against CSRF attacks. This section discusses those considerations as it pertains to servlet environments. Refer to CSRF Considerations for a more general discussion.

It is important to require CSRF for log in requests to protect against forging log in attempts. Spring Security’s servlet support does this out of the box.

Logging Out

It is important to require CSRF for log out requests to protect against forging log out attempts. If CSRF protection is enabled (default), Spring Security’s LogoutFilter to only process HTTP POST. This ensures that log out requires a CSRF token and that a malicious user cannot forcibly log out your users.

The easiest approach is to use a form to log out. If you really want a link, you can use JavaScript to have the link perform a POST (i.e. maybe on a hidden form). For browsers with JavaScript that is disabled, you can optionally have the link take the user to a log out confirmation page that will perform the POST.

If you really want to use HTTP GET with logout you can do so, but remember this is generally not recommended. For example, the following Java Configuration will perform logout with the URL /logout is requested with any HTTP method:

Log out with HTTP GET

Java
Kotlin

@EnableWebSecurity
public class WebSecurityConfig {

	@Bean
	public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
		http
			.logout(logout -> logout
				.logoutRequestMatcher(new AntPathRequestMatcher("/logout"))
			);
		return http.build();
	}
}

@EnableWebSecurity
class SecurityConfig {

    @Bean
    open fun filterChain(http: HttpSecurity): SecurityFilterChain {
       http {
            logout {
                logoutRequestMatcher = AntPathRequestMatcher("/logout")
            }
        }
        return http.build()
    }
}

CSRF and Session Timeouts

By default Spring Security stores the CSRF token in the HttpSession. This can lead to a situation where the session expires which means there is not an expected CSRF token to validate against.

We’ve already discussed general solutions to session timeouts. This section discusses the specifics of CSRF timeouts as it pertains to the servlet support.

It is simple to change storage of the expected CSRF token to be in a cookie. For details, refer to the Custom CsrfTokenRepository section.

If a token does expire, you might want to customize how it is handled by specifying a custom AccessDeniedHandler. The custom AccessDeniedHandler can process the InvalidCsrfTokenException any way you like. For an example of how to customize the AccessDeniedHandler refer to the provided links for both xml and Java configuration.

Multipart (file upload)

We have already discussed how protecting multipart requests (file uploads) from CSRF attacks causes a chicken and the egg problem. This section discusses how to implement placing the CSRF token in the body and url within a servlet application.

More information about using multipart forms with Spring can be found within the 1.1.11. Multipart Resolver section of the Spring reference and the MultipartFilter javadoc.

Place CSRF Token in the Body

We have already discussed the tradeoffs of placing the CSRF token in the body. In this section we will discuss how to configure Spring Security to read the CSRF from the body.

In order to read the CSRF token from the body, the MultipartFilter is specified before the Spring Security filter. Specifying the MultipartFilter before the Spring Security filter means that there is no authorization for invoking the MultipartFilter which means anyone can place temporary files on your server. However, only authorized users will be able to submit a File that is processed by your application. In general, this is the recommended approach because the temporary file upload should have a negligible impact on most servers.

To ensure MultipartFilter is specified before the Spring Security filter with java configuration, users can override beforeSpringSecurityFilterChain as shown below:

Initializer MultipartFilter

Java
Kotlin

public class SecurityApplicationInitializer extends AbstractSecurityWebApplicationInitializer {

	@Override
	protected void beforeSpringSecurityFilterChain(ServletContext servletContext) {
		insertFilters(servletContext, new MultipartFilter());
	}
}

class SecurityApplicationInitializer : AbstractSecurityWebApplicationInitializer() {
    override fun beforeSpringSecurityFilterChain(servletContext: ServletContext?) {
        insertFilters(servletContext, MultipartFilter())
    }
}

To ensure MultipartFilter is specified before the Spring Security filter with XML configuration, users can ensure the <filter-mapping> element of the MultipartFilter is placed before the springSecurityFilterChain within the web.xml as shown below:

web.xml - MultipartFilter

<filter>
	<filter-name>MultipartFilter</filter-name>
	<filter-class>org.springframework.web.multipart.support.MultipartFilter</filter-class>
</filter>
<filter>
	<filter-name>springSecurityFilterChain</filter-name>
	<filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
</filter>
<filter-mapping>
	<filter-name>MultipartFilter</filter-name>
	<url-pattern>/*</url-pattern>
</filter-mapping>
<filter-mapping>
	<filter-name>springSecurityFilterChain</filter-name>
	<url-pattern>/*</url-pattern>
</filter-mapping>

Include CSRF Token in URL

If allowing unauthorized users to upload temporary files is not acceptable, an alternative is to place the MultipartFilter after the Spring Security filter and include the CSRF as a query parameter in the action attribute of the form. Since the CsrfToken is exposed as an HttpServletRequest request attribute, we can use that to create an action with the CSRF token in it. An example with a jsp is shown below

CSRF Token in Action

<form method="post"
	action="./upload?${_csrf.parameterName}=${_csrf.token}"
	enctype="multipart/form-data">

HiddenHttpMethodFilter

We have already discussed the trade-offs of placing the CSRF token in the body.

In Spring’s Servlet support, overriding the HTTP method is done using HiddenHttpMethodFilter. More information can be found in HTTP Method Conversion section of the reference documentation.

Cross Site Request Forgery (CSRF) for Servlet Environments

Using Spring Security CSRF Protection

Use proper HTTP verbs

Configure CSRF Protection

Custom CsrfTokenRepository

Disable CSRF Protection

Include the CSRF Token

Form URL Encoded

Automatic CSRF Token Inclusion

csrfInput Tag

CsrfToken Request Attribute

Ajax and JSON Requests

Automatic Inclusion

Meta tags

csrfMeta tag

CsrfToken Request Attribute

CSRF Considerations

Logging In

Logging Out

CSRF and Session Timeouts

Multipart (file upload)

Place CSRF Token in the Body

Include CSRF Token in URL

HiddenHttpMethodFilter