I found that the cookie in browser is a random string which web server sends to each client for remembering users' information purpose. But I don't understand in programmers viewpoint, what does cookie use for?
For example, I've used EditThisCookie extension in Chrome Browser to read wikipedia.org site's cookie, in the following picture included here. The value of this cookie (sessionId) is useless for programmers (EDIT: I mean I don't extract any information from this cookie, I know the cookie is very important for web developers, so sorry about my poor expression). If I get this cookie, which kind of information I can understand about the users?
Looking for some help! Thank you very much!
The example about cookie
http://i102.photobucket.com/albums/m86/dienkun1/cookie_example_zps455f0dad.png
EDIT: Sorry, I've just expressed my problem in wrong way.
Actually, I am going to write an extension for collecting users' preferences via users' cookie, but I can't understand anything what information can be extracted from cookie. I've read about cookie in many documents, like wikipedia, and all of them just show how to get cookie, the definition of cookie, classified... and nothing about which information we can get from cookie.
Thank you very much!
Why do you say that the sessionId is useless for programmers? It actually can be extremely useful. Somewhere on Wikipedia's servers, they're probably storing quite a bit of information about your session. This could include things like whether you've already hidden one of their fundraising banners (so that it won't keep showing it to you again and again), to things that are required for basic functionality, such as what user you are currently logged in as.
However, Wikipedia is storing this same information for millions of sessions. It needs a way to tie the information back to each individual browser. That sessionId is how it does so. It set the sessionId in a cookie when you first accessed the page, and that cookie gets sent back to the server with every request you make to it now. Then they have code on the back end that reads that sessionId from the cookie and uses it to look up all of the information specific to your session, and do whatever needs to be done with it.
You could of course store the session information itself in the cookies, but there are a couple problems with that. First, there are limits on the size of each cookie, and on the overall size of all cookies for a single domain. Some of the data you want to store might not even fit. But the bigger problem is that cookies can be very easily manipulated by the end user. If you stored the information of who the user is logged in as in a cookie, the user could just change that value to something else, and suddenly be logged in as someone else! Of course, it's also possible that the user could change their sessionId to be some other user's session and suddenly be logged in as them. That's why session IDs need to be as random as possible, and should be long enough that guessing someone else's is basically impossible.
Well, why would someone bother writing a sessionId to a cookie if it's useless?
Cookies are extremely useful when it comes to (e.g) identifying users on your site so you can have them logged in right away, count their visits, track them on your site and even beyond.. only to name a few use cases.
To cite a somewhat popular site (wikipedia.org):
Cookies were designed to be a reliable mechanism for websites to remember stateful information (such as items in a shopping cart) or to record the user's browsing activity (including clicking particular buttons, logging in, or recording which pages were visited by the user as far back as months or years ago).
The most important word here is "stateful".
Related
Is it possible to create a cookie from a first site on the user's browser and remains even if he goes to visit a second site. ( define it as a uid )
No. If you were able to do that there would be huge potential for exploitation.
Cookies are locked down to specific URLs and can only be used on there. A global cookie would be terrible practice as you would be able to alter a user's cookies outside of those defined and used on your own site.
I'm not sure why you would want to do this anyway as there is absolutely no reason to do so. If you want to share a cookie with another site you have, then that is entirely possible by making that user send a request to your site and then giving them a specific cookie upon the request. Unless you have malicious intent, there would be no reason or use for global cookies.
I'm trying to disable writing data in a specific cookie on a website,
At the same time, i want the data to be sent,
So it means, i send cookie data and don't want to receive any,
Is it possible ?
Cookie is just a mechanism to store information at per client basis or in client layer above the session layer. In general people hate cookies cause they can do creepy stuff and some website is using resources on their PC.
When you say I want to store a cookie that I never want to read, its really shady. No browser should allow this sort of cookie. You might want to re-look at your architecture.
But may be I donno what exactly you mean.
I've a forum where anonymous is allowed to post, protected by CAPTCHA. For users convenience, I set a Cookie for such a user which lasts about a month so the user does not get the CAPTCHA over and over again. In the simplest form the cookie is called no_captcha_for_one_month and it's value is 1. When the user returns and posts anonymously, he gets not CAPTCHA.
Anyone seeing the flaw? A forum spammer just needs to fill out the CAPTCHA correctly once and use the cookie information for his bot and there he goes.
I thought about getting creative and using a server-side hash which includes e.g. users IP address and some secret salt to generate the cookie value, but it would still be valid for this IP address, of course.
Someone I get the impression the question is silly and I try to solve something unsolvable.
I would recommend implementing your cookie value + salt implementation not to solve your problem but for security reasons. As explained by this blog post wordpress had a similar, albeit it much more severe, problem due to poor cookie security. In your case a determined spammer could always bypass your CAPTCHA even if the cookie had expired.
In order to solve the proposed problem the only solution that is coming to my mind would be to implement a Forced CAPTCHA algorithm that would override your newly secured cookie if it felt the user was being spammy. Off the top of my head I would use attributes like time since last post, number of posts today, the length of time it took to compose the message on the form, etc.
Edit: I should also mention that you can make your forum less attractive to spammers in the first place by implementing the rel="nofollow" attribute on user submitted links. See Wikipedia.
with such a solution it is always possible to use the cookie for a bot. no matter what you try.
As said below, a cookie can easily be taken from a browser and pasted in a bot code, so the solution isn't robust.
Other solutions:
Find some users posting a lot in the forum and ask them if they are volunteer to be moderator. A forum like the AutoHotkey one uses this system, and this works fine. Spammers tend to avoid active forums where moderation is fast and efficient. They prefer dead forums...
Limit the number of anonymous posts per IP address. Can be annoying for users, but can avoid spam flooding. Should be set up only if you experience such flooding.
Even worse, because you are using a cookie, the spammer doesn't even need to do the CAPTCHA once. Cookies can be changed by the client, they are sent by the browser with the page request, so the client can send whatever it wants. In fact spam requests would come from a script, so it's even easier to fabricate the cookies.
Storing the variable server side sill solve the problem I've mentioned; You set a random hash as the cookie, and have a table that stores the CAPTCHA status on the server. For the spammer to get no CAPTCHA, they would have to guess a hash that has the correct variable stored server side, shich is very hard to do.
The problem you mentioned; the fact that once a month might not be long enough to deter a spammer, you can't get around that. You have to show a CAPTCHA to every real user, as often as you want the spammer to enter one as well. Remember, a CAPTCHA is necessary because you can't tell a spammer from a normal user.
You should have the CAPTCHA show often, it will convince people to sign up anyway.
Encrypt the time (in pico or nano seconds) set it as a input value () & set it in your DataBase with a column name 'hash'
set that in every page & see if it matches the DB.
A Note
I have a very good understanding of sessions and the theory of secure web-based authentication, etc., so please don't start with the basics, or give ambiguous answers. I am not looking for Best Practices, because I am aware of them. I am looking for the real risks behind them, that make the Best Practices what they are.
I have read, and agree with the principals that nothing more than a Session identifier should be stored in a Cookie at any given time.
The Story
However... I've inherited a rusty old app that stores the Username, Password, and an additional ID, in a Cookie, which is checked throughout the site as verification/authorization.
This site is always (can only be) accessed via HTTPS, and depending on your stance, is a "low-risk" website.
The application, in its current state, cannot be re-written in such a way as to handle Sessions - to properly implement such a thing would require, essentially, re-writing the entire application.
The Question
When suggesting to the-powers-that-be that storing their user's IDs/Passwords in plaintext, in a Cookie, is an extremely bad idea, what real risks are involved, considering the connection is always initiated and manipulated via HTTPS?
For example: is the only obvious way to compromise this information via Physical Access to the machine containing the Cookie? What other real risks exist?
HTTPS just protects against a man-in-the-middle attack by encrypting the data that goes across the wire. The information would still be in plain text on the client. So anything on the client's computer can go through that cookie information and extract the pertinent information.
Some other risks include cross-site scripting attacks which can enable cookie theft and who knows what kind of browser vulnerabilities which can enable cookie theft.
A given browser's "cookie jar" might not be stored securely, i.e., an attacker might be able to read it without physical access to the machine, over a LAN, or from a distributed filesystem (e.g., if the machine's storing user homes on a storage server, to allow for roaming), or via an application running on the machine.
Some browsers keep cookies in a file that can be displayed on the computer. IE6 comes to mind.
It seems to me that cookies are not all that restricted to a single site. Lots of advertising uses cookies across multiple sites. If I go to NextTag and look for a Nikon D700 camera then
I see NextTag advertisements on slashdot.org. This is an example of a cross-site cookie. Most users use the same password all over the web so if you store the password to one site and make it even a little easy to get to then malicious folks will sooner or later get to it.
To summarize this would be a very very very bad idea. On sites that I work on we don't save users passwords at all. We convert them to a hash key and save the hash key. That way we can validate the user but if we loose the content then there is no exposure of passwords. And this is on the server side, not the browser side!
Most cookies are limited time credentials. For example, session identifiers that expire after a couple hours or are forgotten when the browser windows. Even if the attacker gains access to the session cookie, they are guaranteed neither continued access to the account nor the ability to prevent the original account holder from logging in. Preventing long term account compromise is one of the reasons users are asked for their old password before being allowed to enter a new one.
A cookie containing a username and password, if disclosed, is much longer lived. Also, many users share their passwords between websites. As others have pointed out, the cookie could easily be disclosed via Cross-Site Scripting.
Finally, is the cookie marked with the "Secure" flag? If its not, an active network attack can easily force the browser to disclose it, even if HTTPS is used to serve the entire site.
People here already mentioned the "man in the middle" attack. The thing is that even with https it is still possible. There are different ways to do this - some of them relay on physical access to the network some of them do not.
The bottom line here is that even with https it is still possible for somebody to insert itself between your app and the browser. Everything will be passed through and will look from the browser exactly the same EXCEPT the server certificate. The intruder will have to send his own instead of the real one.
The browser will detect that there are problems with the certificate - usually it will either be issued to a different dns name or, more likely it will not be verified.
And here is the problem: how this violation is presented to the end user and how end user will react. In older versions of IE all indication of the problem was a small broken lock icon on the right side of the status bar - something which many people would not even notice.
How much risk this introduces depends on what is the environment and who (how trainable) the users are
Two two main vulnerabilities are cross site scripting attacks and someone accessing the user's machine.
Have you thought about just storing a password hash in the cookie instead of the raw password? It would require some coding changes but not nearly as many as swapping out your entire authentication system.
I have a internal website that users log into. This data is saved as a cookie. From there the users go on their merry way. Every so often the application(s) will query the authentication record to determine what permissions the user has.
My question is this: Is it more efficent to just query the cookie for the user data when it is needed or to save the user information in viewstate?
[Edit] As mentioned below, Session is also an option.
Viewstate is specific to the page they are viewing, so its gone once they go along thier merry way. Not a good way to persist data.
Your best bet is to use Forms Authentication, its built in to ASP.NET and you can also shove any user-specific information into the Forms Authentication Ticket's Value. You can get 4000 bytes in (after encrypting) there that should hold whatever you need. It will also take care of allowing and denying users access to pages on the site, and you can set it to expire whenever you need.
Storing in the session is a no-no because it scales VERY poorly (eats up resources on the server), and it can be annoying to users with multiple browser connections to the same server. It is sometimes unavoidable, but you should take great pains to avoid it if you can.
Personally, I prefer using a session to store things, although the other developers here seem to think that's a no-no.
There is one caveat: You may want to store the user's IP in the session and compare it to the user's current IP to help avoid session hijacking. Possibly someone else here has a better idea on how to prevent session hijacking.
You can use session data - that way you know that once you have stored it there, users can't fool around with it by changing the query string.
I would use the cookie method. Session is okay but gets disposed by asp.net on recompile, and you have to use a non session cookie if you want to persist it after session anyway. Also if you ever use a stateserver its essentially doing the same thing (stores session in the db). Session is like a quick and dirty fix, real men use cookies.