I have write a small test case which request the same URL in a loop without resending cookies. After a few minutes my Jetty server crash with an OutOfMemoryError. The cause is that every request produce a new session.
Are there any features of the Jetty server or the servlet API to prevent such attacks?
Consider one of the following techniques:
Don't use an in-memory Session management technique. (Use a database)
Set the Session expiration / timeout lower
Setup a DoSFilter to manage it
Setup a QoSFilter to mitigate the behavior a bit better.
On my website, members can write articles to share info with others in their community. I get random reports that the submit fails, and it appears it is because of session timeout.
If I create a small ajax script to "ping" an action on my ASP.NET MVC controller every few minutes, would that reset the session timeout? Or is there a better way?
An ajax ping is what I do in my Java EE MVC web application to keep the session alive, and it works fine. I don't see why it should not work for a ASP.NET application as well.
I am not sure if there is a better way, though.
Yes, that will do the job.
Independently of the technologies, every time an http request reaches the http server, the session "last access time" is updated to the date the communication has been initiated by the client.
If you ping to the server with a delay less than the session timeout you will preserve the session for ever!
Note: you don't need to ping every minutes if your session time out is 30 minutes. It will overload the network for absolutely nothing. I would recommend the session to ping every 25 minutes for such configuration.
HIH
M.
I am currently debugging some issue about this.
We have a ASP.NET web application and I am debugging on Cassini. When I tried to use IE and send out the request to the server, some time (e.g. in about 20minutes) is needed to process and then send out the response.
In case of multi-tab IE, I tried to send out the requests in different tab at about the same time to the same server but the response is handled only after the one of the response is sent out.
If a new instance of IE is started and the requests are sent out in these different instances, the server can process and send out the response almost simultaneously. After doing some research I found that IIS express may solve my problem, but I cannot. Anyone has experienced similar problem or have I missed out some really important things to check with first?
Thank you for your help.
This is primarily due to ASP.net's session state variable and the fact that only one request at a time may have R/W access to a particular session (as determined by the SessionID cookie).
Any additional requests requiring any form of session access (since Read/Write is the default) will be blocked until the previous request has been completed.
Based on the following links:
http://johnculviner.com/asp-net-concurrent-ajax-requests-and-session-state-blocking/
https://msdn.microsoft.com/en-us/library/ms178581.aspx?f=255&MSPPError=-2147217396
I think that you miss the point that the session is lock all request leaving only one per time to run.
Read about that and why:
Replacing ASP.Net's session entirely
Also : Web app blocked while processing another web app on sharing same session
The reason is that Sessions in ASP.NET are not thread safe. Therefore ASP.NET serializes access to requests from the same session.
If you have a multi-tab IE then your tabs share one session. The first request is executed right off and the other ones are queued. If you have different instances then each of them creates a new session and therefore the request are executed in parallel.
I am trying to "log" forcefully when a user has been inactive and or the session has ended (either by inactivity or more importantly, when the browser has closed).
I dont want to use any silly AJAX solution to perform a post every few minutes for "im alive" or call when the browser is closed.
I was under the impression that if you store an object in Session, and you reach the Session_End event, then you will not be able to gain access to anything stored in Session as its ended.
But from some testing I have done, it appears that this is probably the last chance you can obtain access to the object.
Could this be true? is it reliable?
using ASP.NET 4.0 here.
Typically there are two things done.
The first is that a javascript timer is added to the client, not as a heartbeat, but rather as a reminder. If they are close to the session ending, then it simply says "session is about to end. Are you still there?" If so, then it does the "silly" post to ensure the server keeps the session going. This is purely to be nice to your users.
The second (and point of your question) is that you put something in session_end in order to clean up the session. Reliable? well.. most of the time.
Session_End won't run if the app pool is recycled. However, assuming the app pool is ok then yes it will execute when the session expires. The app pool can be recycled for a LOT of reasons ranging from the app crashing to exceeded memory usage to simply because it's been a while since the last reset. This is configurable in IIS.
Would I trust session_end? No. Not 100%. Of course, I wouldn't put anything inside of a session object that would require me to trust it 100% anyway.
For logging the timeout You can use the Global events to log at timeout. See this link for order of events http://www.techrepublic.com/article/working-with-the-aspnet-globalasax-file/5771721
By default the session expiry seems to be 20 minutes.
Update: I do not want the session to expire until the browser is closed.
Update2: This is my scenario. User logs into site. Plays around the site. Leaves computer to go for a shower (>20 mins ;)). Comes back to computer and should be able to play around. He closes browser, which deletes session cookie. The next time he comes to the site from a new browser instance, he would need to login again.
In PHP I can set session.cookie_lifetime in php.ini to zero to achieve this.
If you want to extend the session beyond 20 minutes, you change the default using the IIS admin or you can set it in the web.config file. For example, to set the timeout to 60 minutes in web.config:
<configuration>
<system.web>
<sessionState timeout="60" />
... other elements omitted ...
</system.web>
... other elements omitted ....
</configuration>
You can do the same for a particular user in code with:
Session.Timeout = 60
Whichever method you choose, you can change the timeout to whatever value you think is reasonable to allow your users to do other things and still maintain their session.
There are downsides of course: for the user, there is the possible security issue of leaving their browser unattended and having it still logged in when someone else starts to use it. For you there is the issue of memory usage on the server - the longer sessions last, the more memory you'll be using at any one time. Whether or not that matters depends on the load on your server.
If you don't want to guesstimate a reasonable extended timeout, you'll need to use one of the other techniques already suggested, requiring some JavaScript running in the browser to ping the server periodically and/or abandon the session when a page is unloaded (provided the user isn't going to another page on your site, of course).
You could set a short session timeout (eg 5 mins) and then get the page to poll the server periodically, either by using Javascript to fire an XmlHttpRequest every 2 minutes, or by having a hidden iframe which points to a page which refreshes itself every 2 minutes.
Once the browser closes, the session would timeout pretty quickly afterwards as there would be nothing to keep it alive.
This is not a new problem, there are several scenarios that must be handled if you want to catch all the ways a session can end, here are general examples of some of them:
The browser instance or tab is closed.
User navigates away from your website using the same browser instance or tab.
The users loses their connection to the internet (this could include power loss to user's computer or any other means).
User walks away from the computer (or in some other way stops interacting with your site).
The server loses power/reboots.
The first two items must be handled by the client sending information to the server, generally you would use javascript to navigate to a logout page that quickly expires the session.
The third and fourth items are normally handled by setting the session state timeout (it can be any amount of time). The amount of time you use is based on finding a value that allows the users to use your site without overwhelming the server. A very rough rule of thumb could be 30 minutes plus or minus 10 minutes. However the appropriate value would probably have to be the subject of another post.
The fifth item is handled based on how you are storing your sessions. Sessions stored in-state will not survive a reboot since they are in the computer's ram. Sessions stored in a db or cookie would survive the reboot. You could handle this as you see fit.
In my limited experience when this issue has come up before, it's been determined that just setting the session timeout to an acceptable value is all that's needed. However it can be done.
This is default. When you have a session, it stores the session in a "Session Cookie", which is automatically deleted when the browser is closed.
If you want to have the session between 2 browser session, you have to set the Cookie.Expired to a date in the feature.
Because the session you talk about is stored by the server, and not the client you can't do what you want.
But consider not using ASP.NET server side session, and instead only rely on cookies.
Unfortunately due to the explicit nature of the web and the fact there is no permanent link between a website server and a users browser it is impossible to tell when a user has closed their browser. There are events and JavaScript which you can implement (e.g. onunload) which you can use to place calls back to the server which in turn could 'kill' a session - Session.Abandon();
You can set the timeout length of a session within the web.config, remember this timeout is based on the time since the last call to the server was placed by the users browser.
Browser timedout did not added.
There's no way to explicitly clear the session if you don't communicate in some way between the client and the server at the point of window closing, so I would expect sending a special URI request to clear the session at the point of receiving a window close message.
My Javascript is not good enough to give you the actual instructions to do that; sorry :(
You cant, as you can't control how the html client response.
Actually why you need to do so? As long as no one can pick up the session to use again, it would expire after that 20 minutes. If resources does matter, set a more aggressive session expiry (most hosting companies did that, which is horribly annoying) or use less objects in session. Try to avoid any kind of object, instead just store the keys for retrieving them, that is a very important design as it helps you to scale your session to a state server when you get big.
Correct me if I am misreading the intent of your question, but the underlying question seems to be less about how to force the session to end when a user closes the browser and more about how to prevent a session from ending until the browser is closed.
I think the real answer to this is to re-evaluate what you are using sessions to do. If you are using them to maintain state, I agree with the other responses that you may be out of luck.
However, a preferred approach is to use a persistent state mechanism with the same scope as the browser session such as a cookie that expires when the browser is closed. That cookie could contain just enough information to re-initiate the session on the server if it has expired since the last request. Combined with a relatively short (5-10 min) session timeout, I think this gives you the best balance between server resource usage and not making the user continually "re-boot" the site.
Oh you have rewritten the question.
That one is absolutely feasible, as long as javascript is alive. Use any timed ajax will do. Check with prototype library http://www.prototypejs.org PeriodicalExecutor or jQuery with the ajax + timer plugin. Setup a dummy page which your executor will call from time to time, so your session is always alive unless if he logouts (kill the ajax timer in the same time) or close browser (which means the executor is killed anyway)