JSF 2.x has already builtin CSRF prevention in flavor of javax.faces.ViewState hidden field in the form when using server side state saving. In JSF 1.x this value was namely pretty weak and too easy predictable (it was actually never intended as CSRF prevention). In JSF 2.0 this has been improved by using a long and strong autogenerated value instead of a rather predictable sequence value and thus making it a robust CSRF prevention.

In JSF 2.2 this is even be further improved by making it a required part of the JSF specification, along with a configurable AES key to encrypt the client side state, in case client side state saving is enabled. New in JSF 2.2 is CSRF protection on GET requests by <protected-views>.

使用JSF 1.x的遗留代码，可以扩展form，在form内增加一个token，token通过SessionListener生成，保存在Session中，代码如下：

CsrfSessionListener

public class CsrfSessionListener implements HttpSessionListener {
    private static final String CSRF_TOKEN_NAME = "CsrfToken";

    @Override
    public void sessionCreated(HttpSessionEvent se) {
        HttpSession session = se.getSession();
        session.setAttribute(CSRF_TOKEN_NAME, UUID.randomUUID().toString());
    }

    @Override
    public void sessionDestroyed(HttpSessionEvent se) {

    }
}

 CsrfForm

public class CsrfForm extends HtmlForm {

    private static final String CSRF_TOKEN_NAME = "CsrfToken";
    private static final String CSRF_TOKEN_ID = "csrf_token";

    @Override
    public void encodeEnd(FacesContext context) throws IOException {
        encodeCsrfTokenInput(context);
        super.encodeEnd(context);
    }

    private void encodeCsrfTokenInput(FacesContext context) throws IOException {
        ResponseWriter responseWriter = context.getResponseWriter();
        responseWriter.startElement("input", null);
        responseWriter.writeAttribute("type", "hidden", null);
        responseWriter.writeAttribute("id", getCsrfInputClientId(context), null);
        responseWriter.writeAttribute("name", CSRF_TOKEN_ID, null);
        responseWriter.writeAttribute("value", getToken(context), "value");
        responseWriter.endElement("input");
    }

    @Override
    public void decode(FacesContext context) {
        Map<String, String> requestMap = context.getExternalContext().getRequestParameterMap();
        String value = requestMap.get(CSRF_TOKEN_ID);

        // check if the token exists
        if (value == null || "null".equals(value) || "".equals(value)) {
            throw new CsrfException("CSRFToken is missing!");
        }

        String token = getToken(context);
        // check the values for equality
        if (!value.equalsIgnoreCase(token)) {
            throw new CsrfException("CSRFToken does not match!");
        }
        super.decode(context);
    }

    private String getCsrfInputClientId(FacesContext context) {
        return getClientId(context) + ":" + CSRF_TOKEN_ID;
    }

    private String getToken(FacesContext context) {
        HttpSession session = (HttpSession) context.getExternalContext().getSession(false);
        return (String) session.getAttribute(CSRF_TOKEN_NAME);
    }

}

然后在faces-config.xml中增加配置，使用CsrfForm:

<component>
  <component-type>javax.faces.HtmlForm</component-type>
  <component-class>org.iata.csrf.CsrfForm</component-class>
</component>

CSRF 攻击的应对之道

CSRF的攻击与防御

Java EE 7: Implementing CSRF Protection with JSF 2.2

Preventing CSRF with JSF 2.0

Tomcat CSRF Prevention Filter

Seam Cross Site Request Forgery