A Case of Invalid Viewstate

Tess Ferrandez

If broken it is, fix it you should

A Case of Invalid Viewstate

  • Comments 38

Last week I was helping a colleague of mine with a viewstate case that turned out to be pretty interesting...


The customer was getting events similar to the following in the eventlog and needed to know why they occurred

Event Type: Information
Event Source: ASP.NET 2.0.50727.0
Event Category: Web Event
Event ID: 1316
Date: 2007-06-11
Time: 09:48:02
User: N/A


Event code: 4009
Event message: Viewstate verification failed. Reason: The viewstate supplied failed integrity check.
Event time: 2007-06-11 09:48:02
Event time (UTC): 2007-06-11 07:48:02
Event ID: 14cc57c05e834de98c7df506a013a706
Event sequence: 10
Event occurrence: 1
Event detail code: 50203

Application information:

Application domain: /LM/w3svc/1/root/MyApp-3-128260216693527710
Trust level: Full
Application Virtual Path: /MyApp
Application Path: c:\inetpub\wwwroot\MyApp\
Machine name: MYMACHINE

Process information:

Process ID: 3640
Process name: w3wp.exe
Request information:
Request URL: http://mymachine/MyApp/MyWebForm.aspx
Request path: /TestBadViewstate/WebForm1.aspx
User host address:
Is authenticated: False
Authentication Type:

ViewStateException information:

Exception message: Invalid viewstate.
Client IP:
Port: 14644
User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.2; WOW64; .NET CLR 2.0.50727; .NET CLR 1.1.4322; .NET CLR 3.0.04324.17; InfoPath.2)
Referer: http://SomeThirdPartySite.com/SomePage.htm
Path: /MyApp/MyWebForm.aspx

Custom event details:

For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp.


And the callstack reported was:

[HttpException (0x80004005): Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that <machineKey> 
configuration specifies the same validationKey and validation algorithm. AutoGenerate cannot be used in a cluster.]

System.Web.UI.ViewStateException.ThrowError(Exception inner, String persistedState, String errorPageMessage, Boolean macValidationError) +119
System.Web.UI.ObjectStateFormatter.Deserialize(String inputString) +252
System.Web.UI.ObjectStateFormatter.System.Web.UI.IStateFormatter.Deserialize(String serializedState) +5
System.Web.UI.Util.DeserializeWithAssert(IStateFormatter formatter, String serializedState) +37
System.Web.UI.HiddenFieldPageStatePersister.Load() +222
System.Web.UI.Page.LoadPageStateFromPersistenceMedium() +80
System.Web.UI.Page.LoadAllState() +35
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +9041
System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +217
System.Web.UI.Page.ProcessRequest() +85
System.Web.UI.Page.ProcessRequestWithNoAssert(HttpContext context) +20
System.Web.UI.Page.ProcessRequest(HttpContext context) +110
ASP.MyPage_aspx.ProcessRequest(HttpContext context) +30
System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +405
System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +65




If you get viewstate errors on 1.1. and dont get events like the above, make sure that you have SP1 installed or at least a version of 1.1 later than http://support.microsoft.com/?id=831150  since this hotfix introduced the type of logging above, which is crucial to troubleshooting most viewstate errors.

Viewstate, as most of you know, is a Base64 encoded string containing information about the state of the controls on the webform.  To avoid tampering the viewstate is validated against the machine key, pagename etc. and if the string is either corrupt in some way such that it cant be Base64 decoded or such that it doesn't pass validation you will get an error like the above.

Typically viewstate errors will occur if

  • You're on a web farm and the machine keys are not consistent on all nodes
  • You're on a web farm and the page is slightly different on one node than ot the others, for example if one node is upgraded to 2.0 and the other is still 1.1 or if some controls used on the page are built differently

For a more comprehensive list see: http://support.microsoft.com/?id=829743


In this particular case they had just upgraded to 2.0 from 1.1, they were not running on a web farm.  The error occurred intermittently and only on two specific pages, but most of the time these pages were served just fine without viewstate errors.

Since it is very unusual for errors like this to occur in a non-web farm scenario, especially intermittently, this issue was very curious.   I have seen that happen sometimes when the client was a mobile device and the viewstate was very large as some mobile devices will only send x kb of data so the issue there would be that the viewstate was corrupted because not all the viewstate was sent.   In this case the client was IE 7.0 so no such luck...

I used Fritz Onion's viewstatedecoderr to decode the viewstate to verify that it wasn't corrupted and sure enough the viewstate was just fine, the contents seemed to be fairly standard textboxes etc.

Lucky break

Lucky for me, and for them:)  I have seen enough encoded viewstate to know what viewstate is supposed to look like, so when i took another look at the eventlog entry i noticed that the persisted state started with dDw...    to most people this probably just looks like mumbojumbo but I happen to know that viewstate on 2.0 is supposed to start with /wE...  in fact when I browsed their site on the internet I could indeed see that the typical viewstate for these affected pages (from the hidden viewstate field in view source) was perfectly normal 2.0 viewstate while the dDw... that was sent to the page is typical for 1.1 viewstate.

Knowing this, the question is now, where does this 1.1. viewstate come from?   This is where the eventlog entry comes in handy again... and if you have jumped ahead a bit you have probably noticed by now that the referer is a htm page http://somethirdpartysite.com/SomePage.htm, in other words. there is nothing wrong with the site itself, the problem is that somehow this 3rd party site is posting 1.1. viewstate to the page, and of course that won't validate well against the new 2.0 page.

Browsing to the 3rd party site and looking at the source for the htm file we can see what we already suspected... the page contains a form, with a hidden viewstate field and the post action for the form is our aspx page, so this 3rd party site apparently did a bit of a hack, copying the viewstate while this site was still 1.1. and posting that viewstate to the form... 

Technically, noone but the aspx page itself should really be allowed to post to the aspx page, so anytime the referer of a post to the aspx page is someone other than itself that is bad, and again, to guard against things like this the viewstate validation exists, but of course it might prove to cause a bit of a troubleshooting headache for you.



The solution in this case was to talk to the 3rd party site, let them know about the upgrade and ask them to avoid posting to the site but rather link to the site or redirect to it since there is no way of knowing how long viewstate will be valid as it can change with any type of upgrade to the page.

If there is a benefit to having the 3rd party site being able to post data and show the results in their proprietary format, a web service would be a pretty good solution.


Until next time


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  • Please add 2 and 8 and type the answer here:
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  • I am encountering a strange error with viewstate on my ASP.net 2.0 app. This is running on a Windows 2003 R2 Server non-web farm environment (IIS 6.0).

    Here is the gist of it.  I have a default.aspx page that is the login page of the application.  I can login with my userid and password, click 'submit' and I am logged in.  Now I click on 'Logout' from within the app.  This logs me out and the app does a Response.Redirect to the default.aspx (which is the login page).  

    Now I do nothing on this page for (approx) 1 hour.  When I then try to login, I get the viewstate error.  This occurs deterministically.

    Any clues?

    -- WP

  • Try clearing your browsers cache / temporary internet files (especially you, William). This solved the problem for me.

    Apparently my browser cached a form containing a no longer valid vievstate. So when the form was submitted it gave this error.

    A Ctrl + F5 (tells IE to bypass all caches and proxies and go grab the latest version) on the form itself actually solved it, but clearing all temporary internet files should also do the trick.

  • Hi Tess,

    Great post, cleared a lot of concepts in my mind. I am getting a weird intermittent Invalid_Viewstate error.

    Some of our .NET 1.1 applications throw these intermittent viewstate errors and the viewstate in the exception all starts with a /we. I was able to decode the viewstate using the 2.0 decoder as well. We have no third party sites linking to our web applications. We are running on a web farm, and the machine validation keys are the same for the web servers.

    Can you suggest what else we should be looking for?

  • To my understanding invalid viewstate could also occur if page is posted before the page is completely loaded.

    Our solution was to catch the exception and redirect to a friendly error message page asking the user to wait until the page is downloaded completely. We also implemented 4GuysFromRolla solution on graying to page until it is loaded completely.

  • Safari will post viewstate from a previous page on a redirect.  At the suggestion of another forum, we explicitly turn off auto-fill on the hidden fields (__VIEWSTATE, etc; document element .setAttribute('autocomplete', 'off')) and in code behind we've set: HttpContext.Current.Response.Cache.SetNoStore()

    But we still get viewstate content from Safari that is not the viewstate we served.  All other form fields are from the right page; it's the content of the viewstate that is incorrect (i.e posted to page A, but clearly belonging to page B).

  • not exactly sure how that could be.  the viewstate is just a form field so unless there is a transfer or some redirect i dont see how the form fields would swithc pages.  Would be interesting to see in the eventlogs who it lists as the referrer to see if it is a different page...

  • Its not that much clear. can u tell clearly, wat to do when we get issue like Viewstate verification failed. Reason: The viewstate supplied failed integrity check.

  • FYI: I vote no to it helping solve my problem, but I learnt something new which is more valuable. You should have a "Did this post benefit you?" rather than did resolve the issue.

  • Hi Tess,

    I am finding this problem. I now that you can't post from one page to a different one. I notice in this log entry that the referer and the requested URL only differ in the port (the requested url uses port 81, whereas the referer comes from the implicit port (80). Will this difference cause the viewstate to fail the check?

    Event Type: 9/10/2008 4:24:52 PM

    Event Source: ASP.NET 2.0.50727.0

    Event Category: Web Event

    Event ID: 1316

    User: N/A

    Event code: 4009

    Event message: Viewstate verification failed. Reason: Viewstate was invalid.

    Event time: 9/10/2008 4:24:52 PM

    Event time (UTC): 9/10/2008 11:24:52 PM

    Event ID: 7e68e559612f408797f12d656be75dd9

    Event sequence: 67724

    Event occurrence: 14

    Event detail code: 50204

    Application information:

       Application domain: /LM/W3SVC/2/root-1-128655536206151424

       Trust level: Full

       Application Virtual Path: /

       Application Path: D:\MySite\XXXXXXXXXXX\Web\

       Machine name: DAA30140WWW004

    Process information:

       Process ID: 5136

       Process name: w3wp.exe


    Request information:

       Request URL: http://xx.mysite.com:81/Evaluations/EvalLaunch.aspx?loid=dd22c304-a48e-4bc9-b59e-141784a5d9a7&evalLvl=5&redirect_url=..Viewstate verification failed. Reason: Viewstate was invalid.fLMSViewstate verification failed. Reason: Viewstate was invalid.fUserTranscriptViewstate verification failed. Reason: Viewstate was invalid.fMainView.aspx

       Request path: /Evaluations/EvalLaunch.aspx

       User host address:


       Is authenticated: False

       Authentication Type:  

       Thread account name: DOMAIN\iusr1

    ViewStateException information:

       Exception message: Invalid viewstate.

       Client IP:

       Port: 48510

       User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0; .NET CLR 1.1.4322; .NET CLR 2.0.50727)

       PersistedState: /wEP...

       Referer: https://xx.mysite.com/Evaluations/EvalLaunch.aspx?loid=dd22c304-a48e-4bc9-b59e-141784a5d9a7&evalLvl=5&redirect_url=..Viewstate verification failed. Reason: Viewstate was invalid.fLMSViewstate verification failed. Reason: Viewstate was invalid.fUserTranscriptViewstate verification failed. Reason: Viewstate was invalid.fMainView.aspx

       Path: /Evaluations/EvalLaunch.aspx

    Custom event details:

  • I was having a problem with the viewstate as well.  I am fairly new to .net and was having a difficult go at the viewstate error.  After attempting a few fixes I read online, I noticed that I had a warning from my form tag in my html.  

    I had forgotten that I was using a masterpage, which already had the form tag in it.  I was running the program on my pc and did not know it was a problem till I moved the app to a more formal dev server.

  • Wow, brains and beauty! two reasons while i'll be visiting your blog again...:-)

  • If you work with web sites in a complex/multi server environment you might be familiar with this error

  • The comments in here helped me to nail down my issue.

    In my case the FORM tag had the action URL to be a different one other than the current page where the postbacks meant to perform certrain actions. Once having the current page in that place, all is working fine now.

    But I still have a doubt that these changes are not required for a Windows 2003 Enterprise edition+SP2. This error was readily reproduced on a W2K3 R2 standard edition. Are there any settings that one need to look out in the R2 editions to correct this issue?

  • Sridhar,

    This should not be platform dependent...


  • ok.. May be you can comemnt on this.. I wish there is a method for page object or a static method some where in the library that helps me call something like IsValidViewState()..(Just like how they have introduced TryParse...) That we we can ignore through code as oppposed to throwing an exception..(I can understand why they have this exception thrown) I wish there is an event that fires before this exception is thrown so that we get a chance to check for it as devolopers...Reson being there are so many spasmmers out there whose sole purpose seems to be to just cause this exception..I am sure you would agree with me that cause any exceptions to happen like very few seconds..is not good...........(I know there are other mechanisms like ip blocking and smart defense ect...)

    I wish this is true for validation exception when some one enters html in querysttring.....These exceptions are such a pain..Though I have not seen yet any performance impact because of these exceptions by spasmer and bots...I am just curious what your thoughts are

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