CSRF in a web appRSS

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  qsoft_develo...

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  CSRF in a web app

  Aug 27, 2018 02:05 PM|qsoft_developer|LINK

  Hi,

  I have a vs2013 web app and I am trying to add csrf protection.

  I tried inserting the following code to the MasterPage:

  protected void Page_Init(object sender, EventArgs e)
          {
              // The code below helps to protect against XSRF attacks
              var requestCookie = Request.Cookies[AntiXsrfTokenKey];
              Guid requestCookieGuidValue;
              if (requestCookie != null && Guid.TryParse(requestCookie.Value, out requestCookieGuidValue))
              {
                  // Use the Anti-XSRF token from the cookie
                  _antiXsrfTokenValue = requestCookie.Value;
                  Page.ViewStateUserKey = _antiXsrfTokenValue;
              }
              else
              {
                  // Generate a new Anti-XSRF token and save to the cookie
                  _antiXsrfTokenValue = Guid.NewGuid().ToString("N");
                  Page.ViewStateUserKey = _antiXsrfTokenValue;
   
                  var responseCookie = new HttpCookie(AntiXsrfTokenKey)
                  {
                      HttpOnly = true,
                      Value = _antiXsrfTokenValue
                  };
                  if (FormsAuthentication.RequireSSL && Request.IsSecureConnection)
                  {
                      responseCookie.Secure = true;
                  }
                  Response.Cookies.Set(responseCookie);
              }
   
              Page.PreLoad += master_Page_PreLoad;
          }
   
          protected void master_Page_PreLoad(object sender, EventArgs e)
          {
              if (!IsPostBack)
              {
                  // Set Anti-XSRF token
                  ViewState[AntiXsrfTokenKey] = Page.ViewStateUserKey;
                  ViewState[AntiXsrfUserNameKey] = Context.User.Identity.Name ?? String.Empty;
              }
              else
              {
                  // Validate the Anti-XSRF token
                  if ((string)ViewState[AntiXsrfTokenKey] != _antiXsrfTokenValue
                      || (string)ViewState[AntiXsrfUserNameKey] != (Context.User.Identity.Name ?? String.Empty))
                  {
                      throw new InvalidOperationException("Validation of Anti-XSRF token failed.");
                  }
              }
          }

  In addition, the application also has a page that is not a content page and it can be opened from one of the content pages using <a> tag (example_Form.aspx).

  I added the following code to the example_Form.aspx:

  ////anti forgery variables
          private const string AntiXsrfTokenKey = "__AntiXsrfToken";
          private const string AntiXsrfUserNameKey = "__AntiXsrfUserName";
          private string _antiXsrfTokenValue;
   
          protected void Page_Init(object sender, EventArgs e)
          {
              // The code below helps to protect against XSRF attacks
              var requestCookie = Request.Cookies[AntiXsrfTokenKey];
              Guid requestCookieGuidValue;
              if (requestCookie != null && Guid.TryParse(requestCookie.Value, out requestCookieGuidValue))
              {
                  // Use the Anti-XSRF token from the cookie
                  _antiXsrfTokenValue = requestCookie.Value;
                  Page.ViewStateUserKey = _antiXsrfTokenValue;
              }
              else
              {
                  // Generate a new Anti-XSRF token and save to the cookie
                  _antiXsrfTokenValue = Guid.NewGuid().ToString("N");
                  Page.ViewStateUserKey = _antiXsrfTokenValue;
   
                  var responseCookie = new HttpCookie(AntiXsrfTokenKey)
                  {
                      HttpOnly = true,
                      Value = _antiXsrfTokenValue
                  };
                  if (FormsAuthentication.RequireSSL && Request.IsSecureConnection)
                  {
                      responseCookie.Secure = true;
                  }
                  Response.Cookies.Set(responseCookie);
              }
   
              Page.PreLoad += master_Page_PreLoad;
          }
   
          protected void master_Page_PreLoad(object sender, EventArgs e)
          {
              if (!IsPostBack)
              {
                  // Set Anti-XSRF token
                  ViewState[AntiXsrfTokenKey] = Page.ViewStateUserKey;
                  ViewState[AntiXsrfUserNameKey] = Context.User.Identity.Name ?? String.Empty;
              }
              else
              {
                  // Validate the Anti-XSRF token
                  if ((string)ViewState[AntiXsrfTokenKey] != _antiXsrfTokenValue
                      || (string)ViewState[AntiXsrfUserNameKey] != (Context.User.Identity.Name ?? String.Empty))
                  {
                      throw new InvalidOperationException("Validation of Anti-XSRF token failed.");
                  }
              }
          }

  Do I also need to add a hidden field to the content page? 

  To test my code I wrote the following HTML  to try and hack my app:

  <html>
  <head>
      <title>test csrf forgery</title>
      <script type ="text/javascript">
          document.form1.submit();
          document.getElementById("ButtonSaveOkay").click();
      </script>
  </head>
  <body>
      <form method="post" action="http://www.example.com/example_Form.aspx?TABLE=MD&STATUS=1" onsubmit="javascript:return WebForm_OnSubmit();" id="form1">
          <div class="aspNetHidden">
              <input type="hidden" name="__LASTFOCUS" id="__LASTFOCUS" value="" />
              <input type="hidden" name="__EVENTTARGET" id="__EVENTTARGET" value="" />
              <input type="hidden" name="__EVENTARGUMENT" id="__EVENTARGUMENT" value="" />
              <input type="hidden" name="__VIEWSTATE" id="__VIEWSTATE" value="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" />
   
          </div>
   
   
          <h1>test csrf forgery</h1>
          <div id="form_fields">
              <div id="UpdatePanel_fields">
                  <div id="MainForm" style="text-align:center;">
                      <input name="x_2" type="text" readonly="readonly" id="x_2" size="6" style="background-color:#EBEBE4;left:2mm;top:1mm;position:absolute;z-index:2;text-align:center;font-size:12px;font-family:monospace;" />
                      <input name="D_5" type="text" id="D_5" value="20180101" />
                      <input name="D_7" type="text" id="D_7" value="20181231" />
                      <input type="submit" name="ButtonSaveOkay" value="save" id="ButtonSaveOkay" />
                  </div>
              </div>
          </div>
      </form>>
  </body>
  </html>

  I logged in to my example.com application and then I opened the HTML code located on my computer. I clicked the submit button and I managed to save a new record using the form.

  What am I missing? What am I doing wrong? 

  I tried running the html code while directing the form action to my localhost, while debugging, and I could see that the HTML file has no problem running server side script. The token is the same. a new Anti-XSRF token is never created.

  I would really appreciate your help.

• • Reply
  mgebhard

  All-Star

  37001 Points

  14928 Posts

  Re: CSRF in a web app

  Aug 27, 2018 03:14 PM|mgebhard|LINK

  See the following.

  https://haacked.com/archive/2009/04/02/csrf-webforms.aspx/

  https://msdn.microsoft.com/en-us/library/ms972969.aspx

• • Reply
  qsoft_develo...

  Member

  35 Points

  229 Posts

  Re: CSRF in a web app

  Aug 29, 2018 06:12 AM|qsoft_developer|LINK

  Hi,

  Thanks for the links but I still can't find the answers to my questions.

  Can you maybe relate to my questions regarding my code? Is there something I am missing? The code I added is what comes with the Master page template in VS2013, so I just need to make sure I am testing it right.