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Storing sensitive information at client-When building an application that uses a client-server model, storing sensitive information, such as user credentials, on the client side may result in its unauthorized disclosure if an application the client is vulnerable to attacks that can compromise the information. For example, consider the use of a cookie for storing sensitive information such as user credentials. A cookie is set attack.

For web applications, the most common mitigation to this problem is to provide the client with a cookie and store the sensitive information on the server. Cookies are created by a web server and is are stored for a certain period of time on the client-side. All subsequent requests to the domain identified by the cookie are made to contain information that was saved in the cookie. If the web application is vulnerable to a cross-site scripting vulnerability, an attacker may be able to read any unencrypted information contained in the cookie.. When the client reconnects to the server, it provides the cookie, which identifies the client to the server, and the server then provides the sensitive information.

Cookies do not protect sensitive information against cross-site scripting (XSS) attacks. An attacker who is able to obtain a cookie either through an XSS attack or directly by attacking the client can obtain the sensitive information from the server using the cookie. This risk is timeboxed if the server invalidates the session after a limited time has elapsed, such as 15 minutes.

A cookie is typically a short string. If it contains sensitive information, that information should be encrypted. Sensitive information includes passwordsA partial list of sensitive information includes user names, passwords, password hashes, credit card numbers, social security numbers, and any other personally identifiable information about the user. For more details about managing passwords, see MSC62-J. Store passwords using a hash function. For more information about securing the memory that holds sensitive information, see MSC59-J. Limit the lifetime of sensitive data.

Noncompliant Code Example

In this noncompliant code example, the login servlet stores the user name and password in the cookie to identify the user for subsequent requests:

protected void doPost(HttpServletRequest request,
    HttpServletResponse response) {

  String// Validate input (omitted)

  String username = request.getParameter("username");
  char[] password = request.getParameter("password").toCharArray();
  boolean rememberMe = Boolean.valueOf(request.getParameter("rememberme"));
  
  LoginService loginService = new LoginServiceImpl();
        
  if (rememberMe) {
    if (request.getCookies()[0] != null && 
      request.getCookies()[0].getValue() != null) {
      String[] value = request.getCookies()[0].getValue().split(";");
      
      if (!loginService.isUserValid(value[0], value[1].toCharArray())) {
        // Set error and return
      } else {
        // Forward to welcome page
      }
    } else {
        boolean validated = loginService.isUserValid(username, password);
       
        if (validated) {
          Cookie loginCookie = new Cookie("credentialsrememberme", username + ";"
  	                           + ";" + new String(password.toString());
          response.addCookie(loginCookie);
          // ... forwardForward to welcome page
        } else {
          // Set error and return
        }
     }
   } else {
     // No remember-me functionality selected
     // Proceed with regular authentication;
     // ... if it fails set error and return
   }
    
  Arrays.fill(password, ' ');
}

However, the attempt to implement the " remember-me " functionality is insecure because sensitive information should not be stored at client-side without strong encryption. an attacker with access to the client machine can obtain this information directly on the client. This code also violates MSC62-J. Store passwords using a hash function. The client may also have transmitted the password in clear unless it encrypted the password or uses HTTPS.

Compliant Solution (Session)

•  TODO - I need to re-do this Dhruv Mohindra

...

This compliant solution stores user information using the HttpSesssion class within the javax.servlet.http package. Because HttpSession objects are server-side, an attacker cannot use XSS or man-in-the-middle attacks to gain direct access to the session information. Rather, the cookie stores a session ID that refers to the user's HttpSession object stored on the server. Consequently, the attacker cannot gain access to the user's account details without first gaining access to the session IDimplements the remember-me functionality by storing the user name and a secure random string in the cookie. It also maintains state in the session using HttpSession.

publicprotected classvoid InsecureServlet extends HttpServlet {
  private UserDAO userDAO;
doPost(HttpServletRequest request,
    HttpServletResponse response) {
  
  // ... Validate input (omitted)

  String privateusername String= login(HttpServletRequest request) {
    List<String> errorsrequest.getParameter("username");
  char[] password = request.getParameter("password").toCharArray();
  boolean rememberMe = Boolean.valueOf(request.getParameter("rememberme"));
  LoginService loginService = new ArrayList<String>LoginServiceImpl();
  boolean validated = false;
  if (rememberMe) {
    if (request.setAttribute("errors", errors);

getCookies()[0] != null &&
     String username = request.getParameter("username");.getCookies()[0].getValue() != null) {
                             
    char  String[] passwordvalue = request.getParameter("password"getCookies()[0].getValue().toCharArraysplit(";");
             
      if (value.length != 2) {
        // Basic input validation Set error and return
      }
             
      if (!usernameloginService.matchesmappingExists("value[\\w]*") || !password.toString().matches("[\\w]*"0], value[1])) { 
        // errors.add("Incorrect user name or password format.");
(username, random) pair is checked
        // returnSet "error.jsp";error and return
      }
    } else {
    UserBean  dbUservalidated = thisloginService.userDAO.lookupisUserValid(username, password);

     if if (!dbUser.checkPassword(passwordvalidated)) {
      errors.add("Passwords do not match.");  // Set error and return
      return "error.jsp";}
    }
        
    HttpSessionString sessionnewRandom = requestloginService.getSessiongetRandomString();
    // InvalidateReset the oldrandom sessionevery idtime
    sessionloginService.invalidatemapUserForRememberMe(username, newRandom);
    HttpSession  // Generate new session idsession = request.getSession();
    session.invalidate();
    session = request.getSession(true);
    // Set session timeout to one15 hourminutes
    session.setMaxInactiveInterval(60 *60 15);
    // Store user bean within the session attribute and a random attribute in session scope
    session.setAttribute("user", dbUserloginService.getUsername());
    Cookie loginCookie = 
       // Clear password char arraynew Cookie("rememberme", username + ";" + newRandom);
    ArraysloginCookie.fill(password, ' ');

    return "welcome.jsp";
  }
}
setHttpOnly(true);
    loginCookie.setSecure(true);
    response.addCookie(loginCookie);
    // ... Forward to welcome page
  } else {
    // No remember-me functionality selected
    // ... Authenticate using isUserValid() and if failed, set error
  }
  Arrays.fill(password, ' ');
}

The server maintains a mapping between user names and secure random strings. When a user selects “Remember me,” the doPost() method checks whether the supplied cookie contains a valid user name and random string pair. If the mapping contains a matching pair, the server authenticates the user and forwards him or her to the welcome page. If not, the server returns an error to the client. If the user selects “Remember me” but the client fails to supply a valid cookie, the server requires the user to authenticate using his or her credentials. If the authentication is successful, the server issues a new cookie with remember-me characteristics.

This solution avoids session-fixation attacks by This solution avoids session fixation attacks [OWASP 2009] by invalidating the current session and creating a new session. It also reduces the window in during which an attacker could perform a session-hijacking attack by setting the session timeout to one15 minutes between client accesses.

Applicability

Violation of this rule places Storing unencrypted sensitive information within cookies, making the information vulnerable to packet sniffing or XSS attacks.

Related Guidelines

Bibliography

on the client makes this information available to anyone who can attack the client.

Bibliography

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