In order to properly secure your application it is important to understand Spring’s WebSocket support.

Spring contains a section titled Flow of Messages that describes how messages flow through the system. It is important to note that Spring Security only secures the clientInboundChannel. Spring Security does not attempt to secure the clientOutboundChannel.

The most important reason for this is performance. For every message that goes in, there are typically many more that go out. Instead of securing the outbound messages, we encourage securing the subscription to the endpoints.

Consider the following scenario. A user visits bank.com and authenticates to their account. The same user opens another tab in their browser and visits evil.com. The Same Origin Policy ensures that evil.com cannot read or write data to bank.com.

With WebSockets the Same Origin Policy does not apply. In fact, unless bank.com explicitly forbids it, evil.com can read and write data on behalf of the user. This means that anything the user can do over the websocket (i.e. transfer money), evil.com can do on that users behalf.

Since SockJS tries to emulate WebSockets it also bypasses the Same Origin Policy. This means developers need to explicitly protect their applications from external domains when using SockJS.

Fortunately, since Spring 4.1.5 Spring’s WebSocket and SockJS support restricts access to the current domain. Spring Security adds an additional layer of protection to provide defence in depth.

By default Spring Security requires the CSRF token in any CONNECT message type. This ensures that only a site that has access to the CSRF token can connect. Since only the Same Origin can access the CSRF token, external domains are not allowed to make a connection.

Typically we need to include the CSRF token in an HTTP header or an HTTP parameter. However, SockJS does not allow for these options. Instead, we must include the token in the Stomp headers

Applications can obtain a CSRF token by accessing the request attribute named _csrf. For example, the following will allow accessing the CsrfToken in a JSP:

var headerName = "${_csrf.headerName}";
var token = "${_csrf.token}";

If you are using static HTML, you can expose the CsrfToken on a REST endpoint. For example, the following would expose the CsrfToken on the URL /csrf

@RestController
public class CsrfController {

    @RequestMapping("/csrf")
    public CsrfToken csrf(CsrfToken token) {
        return token;
    }
}

The javascript can make a REST call to the endpoint and use the response to populate the headerName and the token.

We can now include the token in our Stomp client. For example:

...
var headers = {};
headers[headerName] = token;
stompClient.connect(headers, function(frame) {
  ...

}

If you want to allow other domains to access your site, you can disable Spring Security’s protection. For example, in Java Configuration you can use the following:

@Configuration
public class WebSocketSecurityConfig extends AbstractSecurityWebSocketMessageBrokerConfigurer {

    ...

    @Override
    protected boolean sameOriginDisabled() {
        return true;
    }
}

SockJS may use an transport that leverages an iframe. By default Spring Security will deny the site from being framed to prevent Clickjacking attacks. To allow SockJS frame based transports to work, we need to configure Spring Security to allow the same origin to frame the content.

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();
  }
}

SockJS uses a POST on the CONNECT messages for any HTTP based transport. Typically we need to include the CSRF token in an HTTP header or an HTTP parameter. However, SockJS does not allow for these options. Instead, we must include the token in the Stomp headers as described in Section 20.4.3, “Adding CSRF to Stomp Headers”.

It also means we need to relax our CSRF protection with the web layer. Specifically, we want to disable CSRF protection for our connect URLs. We do NOT want to disable CSRF protection for every URL. Otherwise our site will be vulnerable to CSRF attacks.

We can easily achieve this by providing a CSRF RequestMatcher. Our Java Configuration makes this extremely easy. For example, if our stomp endpoint is "/chat" we can disable CSRF protection for only URLs that start with "/chat/" using the following configuration:

@Configuration
@EnableWebSecurity
public class WebSecurityConfig
    extends WebSecurityConfigurerAdapter {

    @Override
    protected void configure(HttpSecurity http) throws Exception {

        http
            .csrf()
                // ignore our stomp endpoints since they are protected using Stomp headers
                .ignoringAntMatchers("/chat/**")
                .and()
            .headers()
                // allow same origin to frame our site to support iframe SockJS
                .frameOptions().sameOrigin()
                .and()
            .authorizeRequests()

            ...

If we are using XML based configuration, we can use the csrf@request-matcher-ref. For example:

<http ...>
    <csrf request-matcher-ref="csrfMatcher"/>

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

    ...
</http>

<b:bean id="csrfMatcher"
    class="AndRequestMatcher">
    <b:constructor-arg value="#{T(org.springframework.security.web.csrf.CsrfFilter).DEFAULT_CSRF_MATCHER}"/>
    <b:constructor-arg>
        <b:bean class="org.springframework.security.web.util.matcher.NegatedRequestMatcher">
          <b:bean class="org.springframework.security.web.util.matcher.AntPathRequestMatcher">
            <b:constructor-arg value="/chat/**"/>
          </b:bean>
        </b:bean>
    </b:constructor-arg>
</b:bean>