17. Security HTTP Response Headers

This section discusses Spring Security’s support for adding various security headers to the response.

17.1 Default Security Headers

Spring Security allows users to easily inject the default security headers to assist in protecting their application. The default for Spring Security is to include the following headers:

Cache-Control: no-cache, no-store, max-age=0, must-revalidate
Pragma: no-cache
Expires: 0
X-Content-Type-Options: nosniff
Strict-Transport-Security: max-age=31536000 ; includeSubDomains
X-Frame-Options: DENY
X-XSS-Protection: 1; mode=block
[Note]Note

Strict-Transport-Security is only added on HTTPS requests

For additional details on each of these headers, refer to the corresponding sections:

While each of these headers are considered best practice, it should be noted that not all clients utilize the headers, so additional testing is encouraged.

You can customize specific headers. For example, assume that want your HTTP response headers to look like the following:

Cache-Control: no-cache, no-store, max-age=0, must-revalidate
Pragma: no-cache
Expires: 0
X-Content-Type-Options: nosniff
X-Frame-Options: SAMEORIGIN
X-XSS-Protection: 1; mode=block

Specifically, you want all of the default headers with the following customizations:

You can easily do this with the following Java Configuration:

@EnableWebSecurity
public class WebSecurityConfig extends
		WebSecurityConfigurerAdapter {

	@Override
	protected void configure(HttpSecurity http) throws Exception {
		http
			// ...
			.headers()
				.frameOptions().sameOrigin()
				.httpStrictTransportSecurity().disable();
	}
}

Alternatively, if you are using Spring Security XML Configuration, you can use the following:

<http>
	<!-- ... -->

	<headers>
		<frame-options policy="SAMEORIGIN" />
		<hsts disable="true"/>
	</headers>
</http>

If you do not want the defaults to be added and want explicit control over what should be used, you can disable the defaults. An example for both Java and XML based configuration is provided below:

If you are using Spring Security’s Java Configuration the following will only add Cache Control.

@EnableWebSecurity
public class WebSecurityConfig extends
WebSecurityConfigurerAdapter {

@Override
protected void configure(HttpSecurity http) throws Exception {
	http
	// ...
	.headers()
		// do not use any default headers unless explicitly listed
		.defaultsDisabled()
		.cacheControl();
}
}

The following XML will only add Cache Control.

<http>
	<!-- ... -->

	<headers defaults-disabled="true">
		<cache-control/>
	</headers>
</http>

If necessary, you can disable all of the HTTP Security response headers with the following Java Configuration:

@EnableWebSecurity
public class WebSecurityConfig extends
WebSecurityConfigurerAdapter {

@Override
protected void configure(HttpSecurity http) throws Exception {
	http
	// ...
	.headers().disable();
}
}

If necessary, you can disable all of the HTTP Security response headers with the following XML configuration below:

<http>
	<!-- ... -->

	<headers disabled="true" />
</http>

17.1.1 Cache Control

In the past Spring Security required you to provide your own cache control for your web application. This seemed reasonable at the time, but browser caches have evolved to include caches for secure connections as well. This means that a user may view an authenticated page, log out, and then a malicious user can use the browser history to view the cached page. To help mitigate this Spring Security has added cache control support which will insert the following headers into you response.

Cache-Control: no-cache, no-store, max-age=0, must-revalidate
Pragma: no-cache
Expires: 0

Simply adding the <headers> element with no child elements will automatically add Cache Control and quite a few other protections. However, if you only want cache control, you can enable this feature using Spring Security’s XML namespace with the <cache-control> element and the [email protected] attribute.

<http>
	<!-- ... -->

	<headers defaults-disable="true">
		<cache-control />
	</headers>
</http>

Similarly, you can enable only cache control within Java Configuration with the following:

@EnableWebSecurity
public class WebSecurityConfig extends
WebSecurityConfigurerAdapter {

@Override
protected void configure(HttpSecurity http) throws Exception {
	http
	// ...
	.headers()
		.defaultsDisabled()
		.cacheControl();
}
}

If you actually want to cache specific responses, your application can selectively invoke HttpServletResponse.setHeader(String,String) to override the header set by Spring Security. This is useful to ensure things like CSS, JavaScript, and images are properly cached.

When using Spring Web MVC, this is typically done within your configuration. For example, the following configuration will ensure that the cache headers are set for all of your resources:

@EnableWebMvc
public class WebMvcConfiguration extends WebMvcConfigurerAdapter {

	@Override
	public void addResourceHandlers(ResourceHandlerRegistry registry) {
		registry
			.addResourceHandler("/resources/**")
			.addResourceLocations("/resources/")
			.setCachePeriod(31556926);
	}

	// ...
}

17.1.2 Content Type Options

Historically browsers, including Internet Explorer, would try to guess the content type of a request using content sniffing. This allowed browsers to improve the user experience by guessing the content type on resources that had not specified the content type. For example, if a browser encountered a JavaScript file that did not have the content type specified, it would be able to guess the content type and then execute it.

[Note]Note

There are many additional things one should do (i.e. only display the document in a distinct domain, ensure Content-Type header is set, sanitize the document, etc) when allowing content to be uploaded. However, these measures are out of the scope of what Spring Security provides. It is also important to point out when disabling content sniffing, you must specify the content type in order for things to work properly.

The problem with content sniffing is that this allowed malicious users to use polyglots (i.e. a file that is valid as multiple content types) to execute XSS attacks. For example, some sites may allow users to submit a valid postscript document to a website and view it. A malicious user might create a postscript document that is also a valid JavaScript file and execute a XSS attack with it.

Content sniffing can be disabled by adding the following header to our response:

X-Content-Type-Options: nosniff

Just as with the cache control element, the nosniff directive is added by default when using the <headers> element with no child elements. However, if you want more control over which headers are added you can use the <content-type-options> element and the [email protected] attribute as shown below:

<http>
	<!-- ... -->

	<headers defaults-disabled="true">
		<content-type-options />
	</headers>
</http>

The X-Content-Type-Options header is added by default with Spring Security Java configuration. If you want more control over the headers, you can explicitly specify the content type options with the following:

@EnableWebSecurity
public class WebSecurityConfig extends
WebSecurityConfigurerAdapter {

@Override
protected void configure(HttpSecurity http) throws Exception {
	http
	// ...
	.headers()
		.defaultsDisabled()
		.contentTypeOptions();
}
}

17.1.3 HTTP Strict Transport Security (HSTS)

When you type in your bank’s website, do you enter mybank.example.com or do you enter https://mybank.example.com? If you omit the https protocol, you are potentially vulnerable to Man in the Middle attacks. Even if the website performs a redirect to https://mybank.example.com a malicious user could intercept the initial HTTP request and manipulate the response (i.e. redirect to https://mibank.example.com and steal their credentials).

Many users omit the https protocol and this is why HTTP Strict Transport Security (HSTS) was created. Once mybank.example.com is added as a HSTS host, a browser can know ahead of time that any request to mybank.example.com should be interpreted as https://mybank.example.com. This greatly reduces the possibility of a Man in the Middle attack occurring.

[Note]Note

In accordance with RFC6797, the HSTS header is only injected into HTTPS responses. In order for the browser to acknowledge the header, the browser must first trust the CA that signed the SSL certificate used to make the connection (not just the SSL certificate).

One way for a site to be marked as a HSTS host is to have the host preloaded into the browser. Another is to add the "Strict-Transport-Security" header to the response. For example the following would instruct the browser to treat the domain as an HSTS host for a year (there are approximately 31536000 seconds in a year):

Strict-Transport-Security: max-age=31536000 ; includeSubDomains

The optional includeSubDomains directive instructs Spring Security that subdomains (i.e. secure.mybank.example.com) should also be treated as an HSTS domain.

As with the other headers, Spring Security adds HSTS by default. You can customize HSTS headers with the <hsts> element as shown below:

<http>
	<!-- ... -->

	<headers>
		<hsts
			include-subdomains="true"
			max-age-seconds="31536000" />
	</headers>
</http>

Similarly, you can enable only HSTS headers with Java Configuration:

@EnableWebSecurity
public class WebSecurityConfig extends
WebSecurityConfigurerAdapter {

@Override
protected void configure(HttpSecurity http) throws Exception {
	http
	// ...
	.headers()
		.httpStrictTransportSecurity()
			.includeSubdomains(true)
			.maxAgeSeconds(31536000);
}
}

17.1.4 X-Frame-Options

Allowing your website to be added to a frame can be a security issue. For example, using clever CSS styling users could be tricked into clicking on something that they were not intending (video demo). For example, a user that is logged into their bank might click a button that grants access to other users. This sort of attack is known as Clickjacking.

[Note]Note

Another modern approach to dealing with clickjacking is using a Content Security Policy. Spring Security does not provide support for this as the specification is not released and it is quite a bit more complicated. However, you could use the static headers feature to implement this. To stay up to date with this issue and to see how you can implement it with Spring Security refer to SEC-2117

There are a number ways to mitigate clickjacking attacks. For example, to protect legacy browsers from clickjacking attacks you can use frame breaking code. While not perfect, the frame breaking code is the best you can do for the legacy browsers.

A more modern approach to address clickjacking is to use X-Frame-Options header:

X-Frame-Options: DENY

The X-Frame-Options response header instructs the browser to prevent any site with this header in the response from being rendered within a frame. By default, Spring Security disables rendering within an iframe.

You can customize X-Frame-Options with the frame-options element. For example, the following will instruct Spring Security to use "X-Frame-Options: SAMEORIGIN" which allows iframes within the same domain:

<http>
	<!-- ... -->

	<headers>
		<frame-options
		policy="SAMEORIGIN" />
	</headers>
</http>

Similarly, you can customize frame options to use the same origin within Java Configuration using the following:

@EnableWebSecurity
public class WebSecurityConfig extends
WebSecurityConfigurerAdapter {

@Override
protected void configure(HttpSecurity http) throws Exception {
	http
	// ...
	.headers()
		.frameOptions()
			.sameOrigin();
}
}

17.1.5 X-XSS-Protection

Some browsers have built in support for filtering out reflected XSS attacks. This is by no means full proof, but does assist in XSS protection.

The filtering is typically enabled by default, so adding the header typically just ensures it is enabled and instructs the browser what to do when a XSS attack is detected. For example, the filter might try to change the content in the least invasive way to still render everything. At times, this type of replacement can become a XSS vulnerability in itself. Instead, it is best to block the content rather than attempt to fix it. To do this we can add the following header:

X-XSS-Protection: 1; mode=block

This header is included by default. However, we can customize it if we wanted. For example:

<http>
	<!-- ... -->

	<headers>
		<xss-protection block="false"/>
	</headers>
</http>

Similarly, you can customize xss protection within Java Configuration with the following:

@EnableWebSecurity
public class WebSecurityConfig extends
WebSecurityConfigurerAdapter {

@Override
protected void configure(HttpSecurity http) throws Exception {
	http
	// ...
	.headers()
		.xssProtection()
			.block(false);
}
}

17.2 Custom Headers

Spring Security has mechanisms to make it convenient to add the more common security headers to your application. However, it also provides hooks to enable adding custom headers.

17.2.1 Static Headers

There may be times you wish to inject custom security headers into your application that are not supported out of the box. For example, perhaps you wish to have early support for Content Security Policy in order to ensure that resources are only loaded from the same origin. Since support for Content Security Policy has not been finalized, browsers use one of two common extension headers to implement the feature. This means we will need to inject the policy twice. An example of the headers can be seen below:

X-Content-Security-Policy: default-src 'self'
X-WebKit-CSP: default-src 'self'

When using the XML namespace, these headers can be added to the response using the <header> element as shown below:

<http>
	<!-- ... -->

	<headers>
		<header name="X-Content-Security-Policy" value="default-src 'self'"/>
		<header name="X-WebKit-CSP" value="default-src 'self'"/>
	</headers>
</http>

Similarly, the headers could be added to the response using Java Configuration as shown in the following:

@EnableWebSecurity
public class WebSecurityConfig extends
WebSecurityConfigurerAdapter {

@Override
protected void configure(HttpSecurity http) throws Exception {
	http
	// ...
	.headers()
		.addHeaderWriter(new StaticHeadersWriter("X-Content-Security-Policy","default-src 'self'"))
		.addHeaderWriter(new StaticHeadersWriter("X-WebKit-CSP","default-src 'self'"));
}
}

17.2.2 Headers Writer

When the namespace or Java configuration does not support the headers you want, you can create a custom HeadersWriter instance or even provide a custom implementation of the HeadersWriter.

Let’s take a look at an example of using an custom instance of XFrameOptionsHeaderWriter. Perhaps you want to allow framing of content for the same origin. This is easily supported by setting the policy attribute to "SAMEORIGIN", but let’s take a look at a more explicit example using the ref attribute.

<http>
	<!-- ... -->

	<headers>
		<header ref="frameOptionsWriter"/>
	</headers>
</http>
<!-- Requires the c-namespace.
See http://static.springsource.org/spring/docs/3.2.x/spring-framework-reference/html/beans.html#beans-c-namespace
-->
<beans:bean id="frameOptionsWriter"
	class="org.springframework.security.web.header.writers.frameoptions.XFrameOptionsHeaderWriter"
	c:frameOptionsMode="SAMEORIGIN"/>

We could also restrict framing of content to the same origin with Java configuration:

@EnableWebSecurity
public class WebSecurityConfig extends
WebSecurityConfigurerAdapter {

@Override
protected void configure(HttpSecurity http) throws Exception {
	http
	// ...
	.headers()
		.addHeaderWriter(new XFrameOptionsHeaderWriter(XFrameOptionsMode.SAMEORIGIN));
}
}

17.2.3 DelegatingRequestMatcherHeaderWriter

At times you may want to only write a header for certain requests. For example, perhaps you want to only protect your log in page from being framed. You could use the DelegatingRequestMatcherHeaderWriter to do so. When using the XML namespace configuration, this can be done with the following:

<http>
	<!-- ... -->

	<headers>
		<frame-options disabled="true"/>
		<header ref="headerWriter"/>
	</headers>
</http>

<beans:bean id="headerWriter"
	class="org.springframework.security.web.header.writers.DelegatingRequestMatcherHeaderWriter">
	<beans:constructor-arg>
		<bean class="org.springframework.security.web.util.matcher.AntPathRequestMatcher"
			c:pattern="/login"/>
	</beans:constructor-arg>
	<beans:constructor-arg>
		<beans:bean
			class="org.springframework.security.web.header.writers.frameoptions.XFrameOptionsHeaderWriter"/>
	</beans:constructor-arg>
</beans:bean>

We could also prevent framing of content to the log in page using java configuration:

@EnableWebSecurity
public class WebSecurityConfig extends
WebSecurityConfigurerAdapter {

@Override
protected void configure(HttpSecurity http) throws Exception {
	RequestMatcher matcher = new AntPathRequestMatcher("/login");
	DelegatingRequestMatcherHeaderWriter headerWriter =
		new DelegatingRequestMatcherHeaderWriter(matcher,new XFrameOptionsHeaderWriter());
	http
	// ...
	.headers()
		.frameOptions().disabled()
		.addHeaderWriter(headerWriter);
}
}