Imagine the next scenario: a user wants to register to a webpage and fills a form. While he is filling the form, jQuery keeps checking through a regular expression if fields are valid, etc...
Taking the email as the primary key which the user will use after registering to login, the email field needs to be checked with Ajax to let the user know if that email is registered or not. I want to check it with Ajax to avoid sending the full form and emptying it, refreshing page, etc...
So, when the user has ended filling the email field, the Ajax request is sent to the server, something like the next link:
example.com/check.php?email=abcdefg#gmail.com
When check.php receives the email, it asks the database if it exists or not and returns a message like: User already exists if user exists or null if user does not exist.
The question is: if someone digs through my .js and finds out links similar to that, they could use that link to send a large number of requests to find out if those random emails exist. This could lead to heavy use of the database or in the worst cases even crashing and private information leaks.
Someone could do a huge for loop to check emails like:
//Getting the response of the next links
example.com/check.php?email=aaaaaaa#gmail.com // Returns null
example.com/check.php?email=aaaaaab#gmail.com // Returns null
example.com/check.php?email=aaaaaac#gmail.com // Returns null
example.com/check.php?email=aaaaaad#gmail.com // Returns User already exists
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Since i last accepted the answer, i kept investigating this and found the solution to avoid this behaviour. The following code is for JAVA but the logic can be applied to any other server-side language.
Before doing ANY ajax request to the server, I request a token to the server. This token looks like this fmf5p81m6e56n4va3nkfu2ns8n it is made by a simple method, it can, however, be more complex, but this is good to go.
public String getToken() throws UnsupportedEncodingException {
return new BigInteger(130, new SecureRandom()).toString(32);
}
When requesting the token, the server does not only return the token, but also a small script that in case someone uses browser to inspect element (and browser navbar) and such the script will run and the token will be cleared. Servlet returns something like this:
_html += "<head>"
+ "<script> "
+ "window.onload=function(){\n"
+ " document.body.innerHTML = \"\";\n"
+ " }"
+ "window.location.href='http://mywebsite.com' "
+ "</script>"
+ "</head>"
+ "<body>"
+ "[" + token+ "]"
+ "</body>"
+ "</html>";
First empties the body then navigates back to wherever we want. javascript/jquery will however, catch the entire content as string, then I simply extract the string between [ and ]. This token is only available for the next request, so every AJAX request will have its unique token. On the 2nd reques the token just used is deleted.
After I get the token I append it as parameter to whatever link i request, something like this:
ajaxRequestObjet = $.ajax({
url: "http://localhost:8084/mywebsite.com/servlet", //<-- local tomcat server
method: "POST",
data: "type=AJAX&page=some-article&token=fmf5p81m6e56n4va3nkfu2ns8n"
});
This method works fine against someone who inspects the website manually and try to use the links, but what about java/php/IIS servers that do this automaticly?
For this ask for header! Something like this:
boolean isAjax = "XMLHttpRequest".equals(request.getHeader("X-Requested-With"));
It will be true only and only if XMLHttpRequest exists....
There is one last thing to keep in mind. Make sure 'Access-Control-Allow-Origin' header is NOT present in your app to make sure that any javascript NOT in your server wont get the server resources. If this header does not exist, chrome will return this:
XMLHttpRequest cannot load http://localhost:8084/mywebsite.com/servlet. No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost' is therefore not allowed access.
Java server was in tomcat and I had another apache for this tests, this is the small html present in apache which gave the error above:
<html>
<head>
<script src="http://code.jquery.com/jquery-latest.min.js" type="text/javascript"></script>
<script>
ajaxRequestObjet = $.ajax({
url: "http://localhost:8084/mywebsite.com/servlet",
method: "POST",
data: "type=AJAX&page=Token"
});
ajaxRequestObjet.done(function (msg) {
alert(msg);
});
</script>
</head>
<body>
</body>
</html>
While you can not control this 100%... there are a few options..
Try using the same methods that people use with Captcha scripts..
Basically when the user loads the form / page.. You generate a random string/id in their PHP session and store it.. When they send the ajax requests, have your ajax check also append the string/id and require it before allowing a check to perform else return a header of 500 or something..
Using this approach with sessions, you could set a allowed limit of checks (say 5) and once the user has tried more than 5 checks, They are required to reload the page or perform a human check (eg Captcha).. Then it resets their count.. Even allow a total of say 30 within 1 hour / per IP or something.
Also use smart events to trigger when the ajax check is done, eg field/tab change or on a button press.. Or when a valid email is detected.. but say .com.au would trigger twice.
Basically this way, even if someone sniffed your JS files and tried to automate the email checker.. It would require them finding a way to append the string/id that you generate and also limit their amount of requests performed.
Beyond this, there is not to much more you can do easily.. But there are still a few other idea's.
Most of them would work around using a PHP session / cookie.. Say for example if they check and find 3 email addresses.. Then again you set that as a limit and force them to require a manual submission or something.
See how the above suggestion goes for you, any questions do feel free to ask. But may take me a day or two to reply as weekend.. Also research how Captcha scripts work as plenty of source code for them.. As they work on the same idea.
Time Delays will simply look bad / make your site appear slow / bug the user with waiting for a response.
You need to limit the amount of look up's per session / ip address.. Otherwise there is always a way to get past these checks.. Basically once they hit a limit.. Force the user/ip/session to wait a few minutes/hours and verify them with a Captcha script so it can not be scripted...
Javascript Security / Hiding The Source
While you can not do this truly, you can do certain things generate the JS using a PHP page with a JS header.. so <script src='myjscode.php'></script> and this allows PHP to check for a valid session.. So stops external requests to an extent.. But this is mostly useful for allowing JS to be only available behind a membership/login..
Multiple Checks / If Possible In This Case
Depending on your approach, is this for a user to check if they already have an account? If so.. you could combine the email check with something like their name/country/age/dob ... So they would need to select two or three correct matching values before being able to get a check/response from the ajax call?
Maybe not in your case, but just thought would add this as well.
The JavaScript code on your website is executed on the computer of the user, so there is no way you could stop him from digging through your code. Even if you use a code obfuscator (for example, https://www.javascriptobfuscator.com/), the hacker could debug your application and record all requests send to the server.
Everything security-relevant has to happen on the server. You could limit the amount of requests from a specific IP address.
You could protect against brute force attacks with something similar to CSRF tokens:
Assign a server-generated ID to every client session. Each request to check.php should include this ID.
check.php should reject requests that do not include an ID, or include an ID that the server did not generate (to prevent attacks with spoofed IDs). It should also rate limit on ID - if a given ID has made a request in (say) the last second, or a given ID makes more than n requests in a 10 second interval, it should return an error response. This protects against requests from a single session arriving from several IP addresses.
You should also rate limit by IP address to prevent brute-forcing by opening a large number of web application sessions.
There isn't much you can do to prevent an attacker looking up a single, or small number, of specific email addresses - it's an inherent risk with this type of validation.
One approach to resolve this problem could be this:
Suppose you have ajax request calling your server to receive a response from a particular user or client. You can have a table in your database where you provide a unique token for every user or hash value that can be checked every time user makes an ajax request to the server. If the token value matches the user request value than he is a genuine user. You can also record his number of request on the table to ensure he is making legitimate requests. I acknowledge the fact that it may slow down your app performance, but it will be safe option to consider. Note: you need to retrieve the token on your HTML page to send it with ajax.
Please comment to know more. I have been using this approach and there is no problem until now.
Example:
This type of attack can be treated the same as any other brute force attack, where the only effective solution is to use a Captcha. But of course, Captchas are a detriment to UX, so you have to consider if the additional security is worth it, especially for an attack that is very unlikely to happen anyway. That said, you may want to use a Captcha on your registration form anyway, to prevent bots from creating accounts.
This sort of attack has a huge cost for little reward for the attacker. There are billions of possible email addresses to test for. It could only be worth going to great lengths such as this, if the site in question was particularly sensitive, such as some kind of adult site, where the attacker hopes to blackmail users that he finds.
CloudFlare
Not as good as a Captcha solution but the brute force attack might be detected and prevented by CloudFlare's DDoS system. Also, CF can force Tor users to solve a Captcha before accessing your site, which would prevent an attacker from using Tor as a vehicle for the attack.
IP Rate Limiting
Rate limiting on an IP basis has problems because if an attacker decided to undertake a task as huge as this, he will likely be using a Botnet or some other system of multiple machines to launch the attack.
Consider a large organisation such as a University, where all users share the public IP. One of the users launches an attack on your site, and you block his IP, and in the processes blocking everyone else. This countermeasure could actually be used to launch a DoS attack.
Session ID/CRSF Token
Definitely not a solution because the attacker needs to simply make a request to the page first, to obtain the token. It's an additional request to make but only an inconvenience for the attacker.
First of all: I'd URL-encode the mail-address. 'example.com/check.php?email=' . urlencode(abcdefg#gmail.com)
Ad your question: when check.php is called, you can
check, if the user's session and his IP have sent a request during the last seconds
if not, write the user's session, the user's IP plus the current timestamp to a helper-table plus to a cookie and hit your DB
if yes, block the request
But I'm afraid this won't help you from fraud because everyone can check your JavaScript and if someone want's to exploit this, he will find ways.
check.php should depending on the setup either only be accessible internally, or verify from where the connection is made. Take a look at this previous question- I hope it might be what you're looking for. how to verify the requesting server in php?
You could use a CSRF token and exit early from your script if you detect that no or an invalid CSRF token. Almost (if not all) PHP frameworks come with support for this.
Also check this question from the security community: https://security.stackexchange.com/questions/23371/csrf-protection-with-custom-headers-and-without-validating-token
Related
Basically my question is similar to this one:
How to secure php scripts?
with one slight difference, the other side is Shopify.
Background info:
Shopify user bought some credits (Audible style), and wants to know how many he has available. He logs in into his account, and it says there that he has X credits.
That number comes from AJAX call to my server (I have full control), where there is a simple php script which checks the value in db (which is updated using webhooks from Shopify, each of which needs to be verified so they are secure, I think).
The script uses customers ID for a look up, and that value needs to be passed to the script somehow, and that allows someone external to just keep running it until he has all IDs and corresponding credits values.
So, my questions is, how do I stop that? How do I ensure that only authenticated users can check it, and only for their IDs.
There is plenty of info on Shopify docs about securing the connections the other way, i.e. to make sure only correct scripts have access to the Shopify db, but nothing about my problem.
As far as I know I only I only have access to JS on Shopify, which creates the problem, because everything I send to my server is visible to all.
Thanks
EDIT: I just read up on CSRF. I can easily implement checks for origin and headers, but these can be faked, right?
EDIT 2: I got around this problem by using metafields. So, instead of storing all that info on my server's db, I just use Customer Metafields to store the available credits. Webhooks are secure so that's brilliant. It still doesn't solve a problem with the next stage though. Customers will still need to be able to use their credits and get digital products, which are generated by my server. So I still need to verify the requests.
EDIT 3: Comment by #deceze and answer by #Jilu got me thinking. Yes, you are correct, I need to do that, but I don't have access to back-end on Shopify, so I cannot create session. However, what I could do (if I figure out how in js) is hash it. PHP login scripts operate on password_hash. That way you do not store a password in the db. Password get's verified again hash (or whatever you call) in the db, and it's either true or false. If true, you are logged in. So I could try to generate a token using a specific string (make it very long) and user id. Send it with the request, and using password_verify or what not, check it against the users. The one that pops positive is logged in user who requested the information. That is assuming I can hide the string in the Shopify...
Step1: Do a session login system.
Step2: Before the Ajax, generate a random token in your form or request page, put it into a input display none, send it with POST.
Verify each time if the token is set and is the same that you got.
You have now verified if the user is really logged in with session.
And you checked that he is from the right page.
You create a token out of shared secret (both Shopify and server have it), and client ID.
On Shopify:
{% assign my_secret_string = "ShopifyIsAwesome!" | hmac_sha256: "secret_key" %}
My encoded string is: {{ my_secret_string }}
On server:
We gonna be checking received hash value against values in our db, so we need to hash local client IDs using the same algo and key (that probably should be done on receiving the Customer Creation webhook).
Hash IDs using: http://php.net/manual/en/function.hash-hmac.php
$hashed_id = hash_hmac('sha256', '$client_id', 'secret_key');
Compare hash using: http://php.net/manual/en/function.hash-equals.php
$check = hash_equals($hashed_id, $received_id);
Then all that's requires is to loop through the db until you find a match. There may be quicker ways of doing it.
The application I'm working on relies on many popups. Those popups rely themselves on query strings. If someone can just type the url in the browser address bar, the page will throw an error as the query strings values are dynamically constructed.
function myFunction(id)
{
window.open("mypopup.aspx?id=" + id);
}
Is there a why to prevent the page from displaying if the requester of the page is not a Javascript? If someone type something like:
https://mycompanyname.com/path/mypopup.aspx
It shouldn't let the user do so. Or, at least check whether the requester is not javascript so I can display a message or redirect the user to a different page? Otherwise, without all those pieces of data needed to construct a request, the page will throw an exception.
Thanks for helping.
Validate the query string directly in myPopup.aspx, if something is missing just redirect or display a message.
Use the Request.QueryString collection to validate in myPopup.aspx.
There is no easy way to validate if the request came from javascript as far as I know. You could try creating a token to validate that the sender is the one you expect, but if you only need to validate the parameters, no need to worry about who is sending the request.
The page cannot differentiate how it was requested, if both requests come from a same browser.
However, you can include in query string to differentiate them.
For example,
window.open("mypopup.aspx?request=javascript&id=" + id);
If a user intentionally type in https://mycompanyname.com/path/mypopup.aspx?request=javascript, so be it. I won't worry about it.
Popups are browser windows too. So it will be tricky to check if the window requesting the page is normal window or popup.
You should restrict the users to see on what url the popup is being opened you can hide the address bar. So user can not copy or know the what's in the url.
window.open('/pageaddress.html','winname','directories=no,titlebar=no,toolbar=no,location=no,status=no,menubar=no,scrollbars=no,resizable=no,width=400,height=350');
Setup a token based validation. Make request to server(Ajax request) to get a random token(with one time validation mechanism and expire it), You can send the token in the query string and validate it on server if it's same issued token. Identify if the requested page have valid token(popup) otherwise deny the request or show error message. Think of how captcha works, you just need to do it programmatically.
Though it's also not the best solution as token information can be sniffed through network traffic tracker tools like fiddler but it's will work to prevent manual requests.
On my website I have a registration page which makes an AJAX request to check if a username is available after it has been entered. This file is called check.php and is in the same directory as the registration.php file. When data is posted to check.php it will perform a query at a MySQL database and return how many users it found with that username.
If anybody were to post data to the check.php file they would see the result, too. I need to stop this somehow, I've read on a few answers I need to "authenticate" each request. This is probably a very large topic although I'm not too sure what to search for to find more about it. Is authenticating each request a good way to stop unnecessary username checks? If so I would really appreciate it if anyone could point me in the right direction as to how to do this.
A solution is to generate a unique token in session, and put it in all pages that will contain a form. Post this token on each AJAX request you make.
It is called CSRF protection, Cross-Site Request Forgery.
You can add a protection layer checking the user referer in HTTP headers.
Answer for common case: no - you can't prevent this, since AJAX is just an HTTP-request. It can be sent no matter how you'll protect your server. So if the point is - to protect from 'evil hackers' - there's no way to do this. The correct though is to check/validate anything on server side.
But is it's about only basic check, you can read
if (strtolower($_SERVER['HTTP_X_REQUESTED_WITH'])=='xmlhttprequest')
-but be aware - this is also a data, which came from client i.e. it can't be trusted (actually, it's just HTTP-request header, nothing more)
I think you can create a Session variable when the user logs in your aplication and check if this variable has the correct value whe you post something to your 'check.php' file to check if your user is previous authenticate
Missing a lot of info but conceptually I am not sure you are worrying about a real risk. Bottom line is that people can use your form to check if emails exist so it's logical they can use check.php as well. Would be overkill to try and prevent that.
I have one think - you can generate some unique token, store it on SESSION before show the page. Than on each checking you must to add this token to request. check.php must regenerate token and return it new.
But each request can emulate and it not protect you from people, which want to know results of check.php. Nothing protect...
Also you can make mechanism for analyzing ip request for checking
I've got a single page node.js FB Canvas App. Every user action triggers an AJAX POST to my node.js HTTPS server, returning the result.
Now I need a way to send a user token I create from the userId on app boot (this is an AJAX POST too, returning all content + user token). I verify that it is this user by doing a Graph API call (which is required for my boot for another reason) on the server.
Q1 So to create the token what should I use?
Q2 How to send the token with every AJAX call:
POST param?
cookie?
something else?
Q1 I assume that tokens should be unique and secure. That's generally not an easy problem. I would go with following steps:
generate a random number
try to save it into DB (or any other shared storage)
if it already exists in DB go to step 1. if not go to step 4
send the token
Ad.1. To generate a random number use crypto.randomBytes with large enough size param (256 is more then enough) in order to minimize collisions:
http://nodejs.org/api/crypto.html#crypto_crypto_randombytes_size_callback
crypto.randomBytes should be secure. There are however some subtleties with it. For example you have to ensure that your machine has enough entropy. It can be a problem when your server does not have keyboard, mouse or mic. You can always add a hardware entropy generator:
http://en.wikipedia.org/wiki/Hardware_random_number_generator
If you don't need it to be secure then you can use crypto.pseudoRandomBytes instead.
Also it is a good idea to create and use your own algorithm (based on crypto of course). For example add a current date to that number, hash it, whatever. Just be careful not to overdo it.
Also remember about cleaning DB from old tokens.
Q2 It doesn't really matter. Whatever suits you. Probably putting it in a cookie is the easiest solution.
If you need this token for preventing from a CSRF attack, I'd recommend to send it into a POST parameter.
I'm trying to make a bookmarklet that does something similar to what Instapaper's does. I need the bookmarklet to send the URL of the page the user is visiting and the user's token(so the server identifies the user). How can this be done? Do you recommend I send a POST request or rather by routing the URL(for eg http://example.com/USER_TOKEN/URL )?
Also, will I need to worry about the user's token being stolen? If so, how can I handle that?
will I need to worry about the user's token being stolen
Since everything you transmit over plain HTTP is basically unencrypted plain-text, yes, you need to worry about the token being stolen.
What's more important imo, is that including the user token into your bookmarklet seems rather hack-ish:
What if a machine is used by multiple users A, B and C?
Users A and B are both using your service? Separate bookmarklets?
User C is pissed off about something A did - clicking his bookmarklet on a dozen porn sites sure sounds like fun, eh?
I would suggest something along the following lines:
Submit the URL to a GET (if you care about performance much) or POST (if you care about getting CRUD right) route.
Server-Side: Check if a user session exists (via cookies, obviously).
If so, process your data, send success callback as JSONP.
If not, send failure callback as JSONP which triggers a "Please Log in" popup/overlay.
Extra points are given for the "Please log in" thingy remembering the URL the user has been trying to save so he doesn't have to re-submit after having logged in.