CSRF token generation

Question

This is a question about generating CSRF tokens.

Usually I\'d like to generate a token based off of a unique piece of data associated with the user\'s session, and h

Answer 1

Is there any reason why I cannot include the string to hash as part of the request as well?

CSRF tokens have two parts. The token embedded in the form, and a corresponding token somewhere else, be it in a cookie, stored in a session or elsewhere. This use of elsewhere stops a page being self contained.

If you include the string to hash in the request, then the request is self contained, so copying the form is all an attacker needs to do, as they have both parts of the token, and thus there is no protection.

Even putting it in the form URL means that it's self contained, the attacker simply copies the form and the submission URL.

Answer 2

You simply just need the same "token" in the URL/form and in the cookie. This means that you could have your page setting the token cookie to whatever it wants to (preferably some random value) by JavaScript and then just pass the very same value in all requests that goes to your server (as a URI ?param or form-field). No need to have your server generating the cookie.

This is safe as long as we trust that the browser doesn't allow pages from a domain to edit/read cookies for other domains, and this is assumed to be quite secure today.

Having your server generating the token will assume that this token can be safely transmitted to your browser without being picked up by any CSRF attempts (why take the risk?). Though you could put more logic into a server generated token, but to prevent CSRF there is no need.

(If I'm wrong here please let me know)

Answer 3

I think the best idea to make hash based on HMAC, i.e. make hash encrypted by some password this sequence: username+user_id+timestamp. Each request the hash must be different, timestamp must be if you don't want to get simple replay the hash in attack.

Answer 4

CSRF token meant to prevent (unintentional) data modifications, which are usually applied with POST requests.

Thus, you must include CSRF token for each request that changes data (either GET or POST request).

My question is in regards to generating tokens when there is NO unique user data to use. No sessions are available, cookies are not an option, IP address and things of that nature are not reliable.

Then simply create a unique user id for each visitor. Include that id in a cookie or in the URLs (if cookies are disabled).

Edit:

Consider the following event:

You have logged-in to your facebook account and then entered to some arbitrary website.

In that website there's a form that you submit, which tells your browser to send a POST request to your facebook account.

That POST request may change your password or add a comment etc, because that the facebook application recognized you as a registered & logged-in user. (unless there's another blocking mechanism, like CAPTCHA )

Answer 5

With the help of CSRF token we can sure incoming request is authenticated (know user not hacker)

Please note i have required below approach but google can't help me even on stackoverflow i did't get mentioned code below but after collection of stackoverflow answer i have made my day. So it's useful for further searching/ specially for beginners

I have described below Spring MVC with Spring Interceptor

Note - I have used google cache to store salt in cache for re verification

below dependency need to add pom.xml

    <!-- https://mvnrepository.com/artifact/com.google.guava/guava -->
    <dependency>
        <groupId>com.google.guava</groupId>
        <artifactId>guava</artifactId>
        <version>28.0-jre</version>
    </dependency>

below HandlerInterceptorAdapter implemention

    package com.august.security;

    import java.security.SecureRandom;
    import java.util.Enumeration;
    import java.util.LinkedList;
    import java.util.List;
    import java.util.concurrent.TimeUnit;

    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import javax.servlet.http.HttpSession;

    import org.apache.commons.lang3.RandomStringUtils;
    import org.springframework.web.servlet.ModelAndView;
    import org.springframework.web.servlet.handler.HandlerInterceptorAdapter;

    import com.google.common.cache.Cache;
    import com.google.common.cache.CacheBuilder;

    public class CsrfSecurity extends HandlerInterceptorAdapter {
        List<String> urlList= new LinkedList<>();
        private static final String CSRF_TAG = "CSRF-CHECK";

        @SuppressWarnings("unchecked")
        @Override
        public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handleer)
                throws Exception {
            System.out.println("Inside Pre Handler");

            String reqUrl = request.getRequestURI().toString();
            System.out.println("Request URL : " + reqUrl);
            String ipAddress = request.getHeader("X-FORWARDED-FOR");
            if (ipAddress == null) {
                ipAddress = request.getRemoteAddr();
            }
            //local host url http://localhost:8080/august/
            if (request.getRequestURI().contains("/august/")) {
                System.out.println("pre handler return true");
                //it will return and next executed postHandelr method
                //because of on above url my webApplication page working
                return true;
            }
            if (ignoreUrl().contains(request.getRequestURI())) {
                System.out.println("inside ignore uri");
                return true;
            } else {
                System.out.println("CSRF Security intercepter preHandle method started.......");
                String salt = request.getParameter("csrfPreventionSalt");
                HttpSession sessionAttribute = request.getSession();
                Cache<String, Boolean> csrfPreventionSalt = (Cache<String, Boolean>) sessionAttribute
                        .getAttribute("csrfPreventionSalt");
                if (csrfPreventionSalt == null) {
                    System.out.println("Salt not matched session expired..");
                    parameterValuesPrint(request, "saltCacheNotFound");
                    response.sendRedirect("error");
                    return false;
                } else if (salt == null) {
                    parameterValuesPrint(request, "noSaltValue");
                    System.out.println("Potential CSRF detected !! inform ASAP");
                    response.sendRedirect("error");
                    return false;
                } else if (csrfPreventionSalt.getIfPresent(salt) == null) {
                    System.out.println("saltValueMisMatch");
                    System.out.println("Potential CSRF detected !! inform ASAP");
                    response.sendRedirect("error");
                } else {
                    request.setAttribute("csrfPreventionSalt", csrfPreventionSalt);
                }
                return true;
            }

        }

        @SuppressWarnings("unchecked")
        @Override
        public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler,
                ModelAndView modelAndView) {
            System.out.println("Inside post Handler");
            System.out.println("CSRF Security key generator method started");
            try {
                //localhost url http://localhost:8080/august/
                //api is my controller path so no need to genrate token for api
                if (request.getRequestURI().contains("/august/api/")) {
                    System.out.println("No need to genrate salt for api");
                } else {
                    HttpSession sessionAttribute = request.getSession();
                    Cache<String, Boolean> csrfPreventionSaltCache = (Cache<String, Boolean>) sessionAttribute
                            .getAttribute("csrfPreventionSalt");
                    System.out.println("csrfPreventionSaltCache ::: " + csrfPreventionSaltCache);
                    if (csrfPreventionSaltCache == null) {
                        csrfPreventionSaltCache = CacheBuilder.newBuilder().maximumSize(5000)
                                .expireAfterWrite(20, TimeUnit.MINUTES).build();
                        request.getSession().setAttribute("csrfPreventionSaltCache", csrfPreventionSaltCache);
                    }

                    String salt = RandomStringUtils.random(20, 0, 0, true, true, null, new SecureRandom());
                    System.out.println("csrfPreventionSalt genrated ::: " + salt);
                    csrfPreventionSaltCache.put(salt, Boolean.TRUE);
                    if (modelAndView != null) {
                        System.out.println("Model and view not null and salt is added in modelAndView");
                        modelAndView.addObject("csrfPreventionSalt", salt);
                    }
                }
            } catch (Exception ex) {
                System.out.println(ex.getMessage());
                ex.printStackTrace();
            }
        }

        @Override
        public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex)
                throws Exception {
            System.out.println("afterCompletion : ");
            if (ex != null) {
                System.out.println("exception : " + ex.getMessage());
                ex.printStackTrace();
            }
        }

        private List<String> ignoreUrl() {
            if(urlList == null) {
                urlList.add("/august/error");
                //add here your ignored url.
            }
            return urlList;
        }

        private void parameterValuesPrint(HttpServletRequest request, String err) {
            StringBuilder reqParamAndValue = new StringBuilder();
            Enumeration<?> params = request.getParameterNames();
            while (params.hasMoreElements()) {
                Object objOri = params.nextElement();
                String param = (String) objOri;
                String value = request.getParameter(param);
                reqParamAndValue = reqParamAndValue.append(param + "=" + value + ",");
            }
            System.out.println(CSRF_TAG + " " + err + "RequestedURL : " + request.getRequestURL());
        }
    }

Below is Interceptor registration with spring context

package com.august.configuration;

    import org.springframework.context.annotation.Bean;
    import org.springframework.context.annotation.ComponentScan;
    import org.springframework.context.annotation.Configuration;
    import org.springframework.web.servlet.ViewResolver;
    import org.springframework.web.servlet.config.annotation.EnableWebMvc;
    import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
    import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;
    import org.springframework.web.servlet.view.InternalResourceViewResolver;

    import com.august.security.CsrfSecurity;

    @Configuration
    @EnableWebMvc
    @ComponentScan(basePackages="com.august")
    public class SpringConfiguration extends WebMvcConfigurerAdapter  {

        @Bean
        public ViewResolver viewResolver() {
            InternalResourceViewResolver viewResolver = new InternalResourceViewResolver();
            //viewResolver.setViewClass(JstlView.class);
            viewResolver.setPrefix("/WEB-INF/views/");
            viewResolver.setSuffix(".jsp");
            return viewResolver;

        }

        @Bean
        public CsrfSecurity csrfSecurity() {
            return new CsrfSecurity();
        }
        @Override
        public void addInterceptors(InterceptorRegistry registry) {
            registry.addInterceptor(new CsrfSecurity());
        }
    }

below is my controller

    package com.august.v1.appcontroller;

    import javax.servlet.http.HttpSession;

    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.stereotype.Controller;
    import org.springframework.ui.Model;
    import org.springframework.web.bind.annotation.RequestMapping;
    import org.springframework.web.bind.annotation.RequestMethod;


    @Controller
    public class HomeController {

        @Autowired 
        HttpSession httpSession;

        @RequestMapping("/")
        public String index(Model model) {
            httpSession.invalidate();
            System.out.println("Home page loaded");
            return "index";
        }
    }

below is my index.jsp jsp page

    <%@ page language="java" contentType="text/html; charset=ISO-8859-1"
        pageEncoding="ISO-8859-1" isELIgnored="false"%>
         //don't forget to add isELIgnored="false" on old(version) jsp page because of i 
         //have wasted 1 hour for this
    <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
    <html>
    <head>
    <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
    <title>ADS Home</title>
    </head>
    <body>
    <h1>${csrfPreventionSalt}</h1>
    <input type="hidden" name="csrfPreventionSalt" value=${csrfPreventionSalt}>
    </body>
    </html>

For Understanding about CSRF - CSRF explanation

Answer 6

I wanna say your approach works, because CSRF attack is the attacker utilizing victim's browser to forge a logged-in status, why can they do so? because on most server side the session check is based on a SessionID in cookie, and cookie is a piece of data will be automatically attached to a HTTP request sent to server.

Therefore, there are two key factors for defending CSRF

1. Generate a challenge token, and require client to pass it to server in a non-cookie way, either URL param or POST form is ok.
2. Keep the token safe as what you did to the SessionID, for instance, using SSL.

I recommend reading CSRF Prevention Cheat Sheet