486 lines
19 KiB
Plaintext
486 lines
19 KiB
Plaintext
[[servlet-csrf]]
|
||
= Cross Site Request Forgery (CSRF) for Servlet Environments
|
||
|
||
This section discusses Spring Security's xref:features/exploits/csrf.adoc#csrf[Cross Site Request Forgery (CSRF)] support for servlet environments.
|
||
|
||
[[servlet-csrf-using]]
|
||
== Using Spring Security CSRF Protection
|
||
The steps to using Spring Security's CSRF protection are outlined below:
|
||
|
||
* <<servlet-csrf-idempotent,Use proper HTTP verbs>>
|
||
* <<servlet-csrf-configure,Configure CSRF Protection>>
|
||
* <<servlet-csrf-include,Include the CSRF Token>>
|
||
|
||
[[servlet-csrf-idempotent]]
|
||
=== 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 xref:features/exploits/csrf.adoc#csrf-protection-idempotent[Safe Methods Must be Idempotent].
|
||
|
||
[[servlet-csrf-configure]]
|
||
=== 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.
|
||
|
||
[[servlet-csrf-configure-custom-repository]]
|
||
==== 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 <<servlet-csrf-include-ajax-auto,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 https://docs.angularjs.org/api/ng/service/$http#cross-site-request-forgery-xsrf-protection[AngularJS]
|
||
|
||
You can configure `CookieCsrfTokenRepository` in XML using the following:
|
||
|
||
|
||
.Store CSRF Token in a Cookie with XML Configuration
|
||
====
|
||
[source,xml]
|
||
----
|
||
<http>
|
||
<!-- ... -->
|
||
<csrf token-repository-ref="tokenRepository"/>
|
||
</http>
|
||
<b:bean id="tokenRepository"
|
||
class="org.springframework.security.web.csrf.CookieCsrfTokenRepository"
|
||
p:cookieHttpOnly="false"/>
|
||
----
|
||
====
|
||
|
||
[NOTE]
|
||
====
|
||
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
|
||
[source,java,role="primary"]
|
||
----
|
||
@EnableWebSecurity
|
||
public class WebSecurityConfig {
|
||
|
||
@Bean
|
||
public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
|
||
http
|
||
.csrf(csrf -> csrf
|
||
.csrfTokenRepository(CookieCsrfTokenRepository.withHttpOnlyFalse())
|
||
);
|
||
return http.build();
|
||
}
|
||
}
|
||
----
|
||
|
||
.Kotlin
|
||
[source,kotlin,role="secondary"]
|
||
----
|
||
@EnableWebSecurity
|
||
class SecurityConfig {
|
||
|
||
@Bean
|
||
open fun filterChain(http: HttpSecurity): SecurityFilterChain {
|
||
http {
|
||
csrf {
|
||
csrfTokenRepository = CookieCsrfTokenRepository.withHttpOnlyFalse()
|
||
}
|
||
}
|
||
return http.build()
|
||
}
|
||
}
|
||
----
|
||
====
|
||
|
||
[NOTE]
|
||
====
|
||
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` (by using `new CookieCsrfTokenRepository()` instead) to improve security.
|
||
====
|
||
|
||
[[servlet-csrf-configure-disable]]
|
||
==== Disable CSRF Protection
|
||
CSRF protection is enabled by default.
|
||
However, it is simple to disable CSRF protection if it xref:features/exploits/csrf.adoc#csrf-when[makes sense for your application].
|
||
|
||
The XML configuration below will disable CSRF protection.
|
||
|
||
|
||
.Disable CSRF XML Configuration
|
||
====
|
||
[source,xml]
|
||
----
|
||
<http>
|
||
<!-- ... -->
|
||
<csrf disabled="true"/>
|
||
</http>
|
||
----
|
||
====
|
||
|
||
The Java configuration below will disable CSRF protection.
|
||
|
||
.Disable CSRF
|
||
====
|
||
.Java
|
||
[source,java,role="primary"]
|
||
----
|
||
@Configuration
|
||
@EnableWebSecurity
|
||
public class WebSecurityConfig {
|
||
|
||
@Bean
|
||
public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
|
||
http
|
||
.csrf(csrf -> csrf.disable());
|
||
return http.build();
|
||
}
|
||
}
|
||
----
|
||
|
||
.Kotlin
|
||
[source,kotlin,role="secondary"]
|
||
----
|
||
@Configuration
|
||
@EnableWebSecurity
|
||
class SecurityConfig {
|
||
|
||
@Bean
|
||
open fun filterChain(http: HttpSecurity): SecurityFilterChain {
|
||
http {
|
||
csrf {
|
||
disable()
|
||
}
|
||
}
|
||
return http.build()
|
||
}
|
||
}
|
||
----
|
||
====
|
||
|
||
[[servlet-csrf-include]]
|
||
=== Include the CSRF Token
|
||
|
||
In order for the xref:features/exploits/csrf.adoc#csrf-protection-stp[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 https://docs.spring.io/spring-security/site/docs/current/api/org/springframework/security/web/csrf/CsrfFilter.html[CsrfFilter] exposes a https://docs.spring.io/spring-security/site/docs/current/api/org/springframework/security/web/csrf/CsrfToken.html[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 <<servlet-csrf-include-form-attr,form>> or <<servlet-csrf-include-ajax-meta-attr,meta tag>>.
|
||
Fortunately, there are integrations listed below that make including the token in <<servlet-csrf-include-form,form>> and <<servlet-csrf-include-ajax,ajax>> requests even easier.
|
||
|
||
[[servlet-csrf-include-form]]
|
||
==== 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
|
||
====
|
||
[source,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.
|
||
|
||
[[servlet-csrf-include-form-auto]]
|
||
===== Automatic CSRF Token Inclusion
|
||
|
||
Spring Security's CSRF support provides integration with Spring's https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/web/servlet/support/RequestDataValueProcessor.html[RequestDataValueProcessor] via its https://docs.spring.io/spring-security/site/docs/current/api/org/springframework/security/web/servlet/support/csrf/CsrfRequestDataValueProcessor.html[CsrfRequestDataValueProcessor].
|
||
This means that if you leverage https://docs.spring.io/spring/docs/current/spring-framework-reference/web.html#mvc-view-jsp-formtaglib[Spring’s form tag library], https://www.thymeleaf.org/doc/tutorials/2.1/thymeleafspring.html#integration-with-requestdatavalueprocessor[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.
|
||
|
||
[[servlet-csrf-include-form-tag]]
|
||
===== csrfInput Tag
|
||
|
||
If you are using JSPs, then you can use https://docs.spring.io/spring/docs/current/spring-framework-reference/web.html#mvc-view-jsp-formtaglib[Spring’s form tag library].
|
||
However, if that is not an option, you can also easily include the token with the xref:servlet/integrations/jsp-taglibs.adoc#taglibs-csrfinput[csrfInput] tag.
|
||
|
||
[[servlet-csrf-include-form-attr]]
|
||
===== CsrfToken Request Attribute
|
||
|
||
If the <<servlet-csrf-include,other options>> for including the actual CSRF token in the request do not work, you can take advantage of the fact that the `CsrfToken` <<servlet-csrf-include,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
|
||
====
|
||
[source,xml]
|
||
----
|
||
<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>
|
||
----
|
||
====
|
||
|
||
[[servlet-csrf-include-ajax]]
|
||
==== 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.
|
||
|
||
[[servlet-csrf-include-ajax-auto]]
|
||
===== Automatic Inclusion
|
||
|
||
Spring Security can easily be <<servlet-csrf-configure-custom-repository,configured>> to store the expected CSRF token in a cookie.
|
||
By storing the expected CSRF in a cookie, JavaScript frameworks like https://docs.angularjs.org/api/ng/service/$http#cross-site-request-forgery-xsrf-protection[AngularJS] will automatically include the actual CSRF token in the HTTP request headers.
|
||
|
||
[[servlet-csrf-include-ajax-meta]]
|
||
===== Meta tags
|
||
|
||
An alternative pattern to <<servlet-csrf-include-form-auto,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
|
||
====
|
||
[source,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
|
||
====
|
||
[source,javascript]
|
||
----
|
||
$(function () {
|
||
var token = $("meta[name='_csrf']").attr("content");
|
||
var header = $("meta[name='_csrf_header']").attr("content");
|
||
$(document).ajaxSend(function(e, xhr, options) {
|
||
xhr.setRequestHeader(header, token);
|
||
});
|
||
});
|
||
----
|
||
====
|
||
|
||
[[servlet-csrf-include-ajax-meta-tag]]
|
||
====== csrfMeta tag
|
||
|
||
If you are using JSPs a simple way to write the CSRF token to the `meta` tags is by leveraging the xref:servlet/integrations/jsp-taglibs.adoc#taglibs-csrfmeta[csrfMeta] tag.
|
||
|
||
[[servlet-csrf-include-ajax-meta-attr]]
|
||
====== CsrfToken Request Attribute
|
||
|
||
If the <<servlet-csrf-include,other options>> for including the actual CSRF token in the request do not work, you can take advantage of the fact that the `CsrfToken` <<servlet-csrf-include,is exposed>> as an `HttpServletRequest` attribute named `_csrf`.
|
||
An example of doing this with a JSP is shown below:
|
||
|
||
.CSRF meta tag JSP
|
||
====
|
||
[source,html]
|
||
----
|
||
<html>
|
||
<head>
|
||
<meta name="_csrf" content="${_csrf.token}"/>
|
||
<!-- default header name is X-CSRF-TOKEN -->
|
||
<meta name="_csrf_header" content="${_csrf.headerName}"/>
|
||
<!-- ... -->
|
||
</head>
|
||
<!-- ... -->
|
||
----
|
||
====
|
||
|
||
[[servlet-csrf-considerations]]
|
||
== 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 xref:features/exploits/csrf.adoc#csrf-considerations[CSRF Considerations] for a more general discussion.
|
||
|
||
|
||
[[servlet-considerations-csrf-login]]
|
||
=== Logging In
|
||
|
||
It is important to xref:features/exploits/csrf.adoc#csrf-considerations-login[require CSRF for log in] requests to protect against forging log in attempts.
|
||
Spring Security's servlet support does this out of the box.
|
||
|
||
[[servlet-considerations-csrf-logout]]
|
||
=== Logging Out
|
||
|
||
It is important to xref:features/exploits/csrf.adoc#csrf-considerations-logout[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
|
||
[source,java,role="primary"]
|
||
----
|
||
@EnableWebSecurity
|
||
public class WebSecurityConfig {
|
||
|
||
@Bean
|
||
public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
|
||
http
|
||
.logout(logout -> logout
|
||
.logoutRequestMatcher(new AntPathRequestMatcher("/logout"))
|
||
);
|
||
return http.build();
|
||
}
|
||
}
|
||
----
|
||
|
||
.Kotlin
|
||
[source,kotlin,role="secondary"]
|
||
----
|
||
@EnableWebSecurity
|
||
class SecurityConfig {
|
||
|
||
@Bean
|
||
open fun filterChain(http: HttpSecurity): SecurityFilterChain {
|
||
http {
|
||
logout {
|
||
logoutRequestMatcher = AntPathRequestMatcher("/logout")
|
||
}
|
||
}
|
||
return http.build()
|
||
}
|
||
}
|
||
----
|
||
====
|
||
|
||
|
||
[[servlet-considerations-csrf-timeouts]]
|
||
=== 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 xref:features/exploits/csrf.adoc#csrf-considerations-login[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 <<servlet-csrf-configure-custom-repository>> 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 xref:servlet/appendix/namespace/http.adoc#nsa-access-denied-handler[xml] and {gh-url}/config/src/test/java/org/springframework/security/config/annotation/web/configurers/NamespaceHttpServerAccessDeniedHandlerTests.java#L64[Java configuration].
|
||
// FIXME: We should add a custom AccessDeniedHandler section in the reference and update the links above
|
||
|
||
|
||
[[servlet-csrf-considerations-multipart]]
|
||
=== Multipart (file upload)
|
||
We have xref:features/exploits/csrf.adoc#csrf-considerations-multipart[already discussed] how protecting multipart requests (file uploads) from CSRF attacks causes a https://en.wikipedia.org/wiki/Chicken_or_the_egg[chicken and the egg] problem.
|
||
This section discusses how to implement placing the CSRF token in the <<servlet-csrf-considerations-multipart-body,body>> and <<servlet-csrf-considerations-multipart-url,url>> within a servlet application.
|
||
|
||
[NOTE]
|
||
====
|
||
More information about using multipart forms with Spring can be found within the https://docs.spring.io/spring/docs/5.2.x/spring-framework-reference/web.html#mvc-multipart[1.1.11. Multipart Resolver] section of the Spring reference and the https://docs.spring.io/spring/docs/5.2.x/javadoc-api/org/springframework/web/multipart/support/MultipartFilter.html[MultipartFilter javadoc].
|
||
====
|
||
|
||
[[servlet-csrf-considerations-multipart-body]]
|
||
==== Place CSRF Token in the Body
|
||
|
||
We have xref:features/exploits/csrf.adoc#csrf-considerations-multipart-body[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.
|
||
|
||
// FIXME: Document Spring Boot
|
||
|
||
To ensure `MultipartFilter` is specified before the Spring Security filter with java configuration, users can override beforeSpringSecurityFilterChain as shown below:
|
||
|
||
.Initializer MultipartFilter
|
||
====
|
||
.Java
|
||
[source,java,role="primary"]
|
||
----
|
||
public class SecurityApplicationInitializer extends AbstractSecurityWebApplicationInitializer {
|
||
|
||
@Override
|
||
protected void beforeSpringSecurityFilterChain(ServletContext servletContext) {
|
||
insertFilters(servletContext, new MultipartFilter());
|
||
}
|
||
}
|
||
----
|
||
|
||
.Kotlin
|
||
[source,kotlin,role="secondary"]
|
||
----
|
||
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
|
||
====
|
||
[source,xml]
|
||
----
|
||
<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>
|
||
----
|
||
====
|
||
|
||
[[servlet-csrf-considerations-multipart-url]]
|
||
==== 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` <<servlet-csrf-include,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
|
||
====
|
||
[source,html]
|
||
----
|
||
<form method="post"
|
||
action="./upload?${_csrf.parameterName}=${_csrf.token}"
|
||
enctype="multipart/form-data">
|
||
----
|
||
====
|
||
|
||
[[servlet-csrf-considerations-override-method]]
|
||
=== HiddenHttpMethodFilter
|
||
We have xref:features/exploits/csrf.adoc#csrf-considerations-multipart-body[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 https://docs.spring.io/spring-framework/docs/5.2.x/javadoc-api/org/springframework/web/filter/reactive/HiddenHttpMethodFilter.html[HiddenHttpMethodFilter].
|
||
More information can be found in https://docs.spring.io/spring/docs/5.2.x/spring-framework-reference/web.html#mvc-rest-method-conversion[HTTP Method Conversion] section of the reference documentation.
|