Is Your AJAX App Secure?

ShaolinTiger writes "An article looking in detail at some of the security problems with AJAX, how to find them and how to approach them or fix them. Security with AJAX is of course an important consideration as it's asychronous and a malicious user could write data back to your database if implemented incorrectly."

JUG

Well, I'd like to say that this is an issue rarely addressed--which is alarming considering how widely AJAX is used these days.

In the article, he addresses a token used to generate random strings:

One should let the page, or some include javascript, generated on the server side, include some token that the performs some operation on which gives a result which is used in any consecutive request to the webserver. The webserver should not allow any request with another 'sequence number', so to speak.

The servers' 'challenge-string' should be as random as possible in order to make it non-predictable: if one could guess what the next sequence number will be, it is again wide open for abuse.

And I think one of the most commonly used Universally Unique IDentifiers (UUID) generators is Java UUID Generator (JUG) [safehaus.org] which can be used by any type of application that can communicate with Java libraries (most apps capable of XML messaging can anyways).

Of course, this can be no better than pseudorandom [wikipedia.org] as we all remember from our courses. :-)

Re:JUG

It should also be possible to add a function that you run for each http request that filters the request for common attacks, and also handles the key the parent talks about.

So when you're writing a command to make a request, you pass your request into your pre-written function which has any request-related security processes written into it. This way things are reasonably seamless in that you don't have to worry about security every time. I think.

/relative JS noob who writes a lot of actionscript so therefore *thinks* he knows a language ;o)

ny

I feel like I am entering the twilight zone...

This is an issue that has not changed one bit since the dawn of the web: Everything that comes in your server through an HTTP(S) request is to be assumed 'insecure' by definition. The only assumption one can make about such data is that it comes from a specific user if a proper session id is provided, nothing else.

This is a very very very common misconception in almost every application I have worked on. People (devs) seems all to think that a javascript consistency check is all it takes to ensure the user will not submit an amount too high, or anything else for that matter.

The approach is flawed because of one thing: Everything that runs out of your box can be fooled with. And JavaScript is so easy to fool with that it is a shame that ANYONE would rely on any piece of JavaScript without any security/safety check on the server side.

AJAX is just another extension based on the same principle. Anyone can fool an HTTP request. Anyone can fool a Browser. Anyone can execute arbitrary Javascript code in your browser to modify its behavior: Just type the code in the address bar.

This issue is just insane!

Is Your AJAX App Secure?: As secure as any webapp. Consistency and security checks needs to be made on every data coming in your system. Short of that, it is just swiss cheese: Full of holes.

it's not secure, check out googe maps

AJAX is not secure! if you look at google maps you can see my house... it's just sitting there on the screen waiting to be bombed. ahh.. my frickin' house!

Tinfoil Response

You sir, are a sucker. I have found a way to beat the dreaded AJAX Google Maps insecurities. Simply put, I have a new house built every couple of years. My current house will be done in a week or so, and according to Google Maps (evil AJAX house bombing helper) my new cul-de-sac does not even exist. It's just a lot of trees... now who would bomb trees?

Please please please, buy a new house, or next time the Google Spyplane comes to take pictures, teepee your neighborhood with Tinfoil, I'm sure your neighbors will understand once you explain it to them.

How is this different

How is this different from securing a "normal" dynamic website?

Re:How is this different

There was a new buzzword in the middle of the sentence.

Re:How is this different

You are absolutely correct. The example the author provides of the .len paramter not being checked by the web app is a prime example of the kinds of problems that plague any web application, AJAX or not. Input validation, session validation, user authentication and so forth are required by EVERY web application. This part particularly irritated me:

If the XmlHttp-interface is merely protected by cookies, exploiting this is all the easier: the moment you get the browser to make a request to that website, your browser is happily sending any cookies along with it.

That is true of most common methods of session management. For instance, PHP's very own built-in session management, which many people use, uses nothing more than a cookie value to manage the session. If you want to secure any web-app that uses sessions through cookies (again, AJAX or not) you'd better be using an HTTPS connection and cookies that are flagged to only be transmitted across a secure connection, and the author never touches on this point.

Add to that the whole nonsense about POST being "more secure" or "harder to fake" and it becomes clear that these are the words of a novice web programmer. And clearly this article illustrates nothing more than a web programmer's first experiences with examining the security of a web app.

But, he's linked to slashdot's main page, with plenty of AdSense links... so good for him.

semantics of GET and POST

Your remark really concludes this topic, and I think any further remarks are redundant. I just want to point out that in the HTTP specification (RFC 2616) section 13.9, it says the following about GET requests:

Unless the origin server explicitly prohibits the caching of their responses, the application of GET and HEAD methods to any resources SHOULD NOT have side effects that would lead to erroneous behavior if these responses are taken from a cache.

And in section 9.5, about POST requests:

Responses to this method are not cacheable, unless the response includes appropriate Cache-Control or Expires header fields.

Thus, the only semantic difference between GET and POST is only on side effects. There is no sense in saying one is more secure than another, or one is easier to fake than another.

If we think of a web server as a function, GET requests means that, let y1 = f(x1) and y2 = f(x2), then x1 = x2 implies y1 = y2. POST requests means there exists y1 and y2, y1 != y2, such that y1 = f(x) and y2 = f(x) for some two applications of f with x. Here y, y1 and y2 are the "web pages" (more generally, resources), and x1, x2, x are the HTTP requests.

Of course, for a practical, dynamic website, the functional property does not usually hold, and that's why we have "cahce control", which attempts to establish what functional property holds under certain conditions.

Obligatory

I write only static HTML you insensitive clod.

But we already know this...

Pretty much everything in this article seems to be a complete rehash of things most web developers should already know, you should always be checking for possible xss/css problems, you should never depend on a cookie, never provide more information to the user than they absolutely require, always treat all input as tainted until it has been correctly validated, just because this article relates to a new technology doesn't mean it is refering to new vulnerabilities.

I am sure that some people can learn a little about security from this article but if you learn anything new reading this, you should go to any sites you have written in the past and take them down right away because chances are you already have a security hole. I recall quite recently a friend of mine was quite shocked that his AJAX application could perform sql injection attacks on his database, on looking at his code he was entirely trusting everything that came to it, I almost slapped him for that mistake.

AJAX App Secure?

If not, you need to clean it up! [colgate.com]
Code cleanliness is next to Dev godliness.

Challenges of AJAX

Security with AJAX is of course an important consideration as it's asychronous and a malicious user could write data back to your database if implemented incorrectly.

That statement is a little misleading, as security is not directly related to requests being asynchronous. I think what the poster meant is that being asynchronous, AJAX application make lots of calls to the back end. In a non-AJAX app, typically you fetch the data during the page load. In AJAX app, users request sections of the page to be refreshed, meaning a lot more finely grained methods to the backend are exposed.

non-AJAX:
    LoadMainPage()
AJAX:
    LoadTitles()
    LoadSections()
    LoadSummary()

Enough already

I am growing sick of hype surrounding the AJAX bandwagon. It reminds me of the mid 1990's when the advent of Java had folks proclaiming how web based applications would be the preferred way of creating new applications across the board. Yeah, right. In short, web based apps have their purpose and can be effective. But they aren't the savior to mankind and the AJAX delivery method has been around for years now. We didn't use crudely fashioned stone tools then either.

And no, I'm not a hater. I personally count Ruby amongst my programming languages of choice and I have written a couple of Rails applications that my company currently has in production. But the AJAX hype is getting tired.

Isn't that always a threat?

Hasn't the threat of a SQL injection always been a threat, dating back to the pre-AJAX days of development? Why is this even news? Proper error handling and input checking should be enough to minimize these problems.

Poor article.

It runs through various ways in which your AJAX app can be insecure. All of which apply to any dynamic page, AJAX or no.
Then, instead of discussing how to, i dunno, say, actually _check_ your input, it rambles through various techniques of that stalwart of crappy coders: security by obscurity.
Every solution posited finishes with "Hey, people could still crack this easily, but it makes it that bit more annoying".

Time here would be much better spent reading some Shiflett (for php newbs of the world), or any "Security goofs 101 and how to _actually_ avoid them", not this "vaguely obfuscate stuff, and use POST" recommendation.

1/10

Something new ?

i fail to see the difference of a webbrowser initiated and a scripted request to a dynamicly generated response. In any way, permission must be checked, the script shall now work on request data nor send data back to a client with insufficient permission. Nothing to see here, move along ... -S

Asynchronous?

No, security is not important because AJAX is asynchronous - security is important because an AJAX app is exposed to unknown users on the public Internet. The security issues with AJAX are the same as with any web application: don't trust any input and validate it before doing anything important with it. The security issues with the Javascript part (things like, but not limited to cross site scripting and sending things to your clients that may be harmful to them) are the same as any other Javascript-using website.

Maybe I'm stupid

Can someone explain to me why this is not a problem with regular GET and POST requests? What is special about AJAX that introduces new security problems? Or is this just a chance to write an article using the latest buzzword?

asynchronous?

what does the author mean using this word in this context? yes I looked it up [reference.com]

Sequence numbering? For sure?

A possible way of securing one's application is using some form of 'sequence-numbering'-like scheme.

How is this not security through obscurity? The only difference between guessing this sequence number and guessing the session ID in a cookie is only that of duration, but one sniff on the wire and you got it.

Overall, the hype on AJAX security stems from people not treating the AJAX requests any differently from non-AJAX requests. Trusting your input is mistake #1 regardless of where or how it comes.

And we'll rehash this entire deal in a few years when AJAX is replaced with something else of equal buzzwordthyness.

Re:Sequence numbering? For sure?

The only difference between guessing this sequence number and guessing the session ID in a cookie is only that of duration

Not quite. The article does a horrible job in explaining it, but basically, one problem is that if an attacker can induce you to view a page containing JavaScript, that JavaScript can execute GET and POST requests under your authority.

So, for example, if the attacker knows that you use Foo Webapp, then he can put up a page on his own site that executes requests corersponding to that web application, and send you a link saying "hey, look at this!" or whatever.

Here's the thing - because it's your browser making the requests, and because those requests are going to Foo WebApp's domain, your browser will send your cookies along with the request, proving that it's you.

What this means is that you not only have to prove that it's you making the request, you also have to prove that it's a request you meant to make. User authentication alone is not enough.

The typical solution to this is to additionally include another random cookie-type value as a hidden field in every form you generate. Because your attacker doesn't have access to the pages you are viewing, he won't have access to that value, so he can't construct forms that submit that value to Foo WebApp. In this way, you can reliably determine that it's a valid form submission that comes from your own web application.

None of this, of course, is dependent upon Ajax being used. Ajax is a red herring here. This security concern applies to all web applications, whether or not they use Ajax.

POST is more secure, WTF?

He states POST is more secure because it is harder to fake?? Nice joke.

What?

What difference does asyncronicity make with security? Zero.

What difference should AJAX make with security? Zero.

All security should be applied on the server-side portion of your AJAX application. The same way any other web application is secured. End of question.

Can someone explain...?

Could someone please explain to me how these potential problems with AJAX requests are unique to AJAX at all? This article did a horrible job at that. Couldn't any GET (to a script) or POST request request be "faked?" Aren't forms and links just as vulnerable to variable insertion and whatnot? AFAIK, there is really no fundamental different between an HTTP request made by a user directly and XmlHTTPRequest.

-matthew

This is security advice?

This author of this article does not seem to properly comprehend security issues. He rambles on for several pages, but doesn't actually propose anything novel or indeed anything particularly useful.

Using POST instead of GET and checking for User Agents and Referer headers won't do much to make your web application anymore secure. It's the web equivalent of hiding the keys under the doormat. Sure, it's better than leaving your door wide open, but it's not security in any meaningful sense of the word.

The way to secure AJAX is the same way classic CGI transactions are secured; through sessions, passwords and SSL.

without RTFA ....

1. verify your data, i have a bunch of asp functions that each convert any input into a string/int/decimal/bool,date that return ""/0/0.0/false/(now) upon chocking on their inputs, simple

2. use regular expressions, strip out the naugty chars from your inputs where you can, like newlines, even semicolons (no one i know has a semi colon in their name, date of birth or email address), and HTML encode your data BEFORE you try to save it to your db, gets rid of the double quotes AND saves time encoding it for every page write.

3. generate unique ids. easy way: generate a long random number, and then add the date and time of the request to the end. sure the right hand half is somewhat guessable but it ensures uniqueness*, which is always handy.

4. FFS dont assume that a user will only click links, anything that comes from the get or post needs double checking against the user's permissions. a lot of security flaws have been found this way: log in, view your bank account, change the url from viewuseraccount.asp?id=1234 to viewuseraccount.asp?1235 ... i'd expect to be fired for making it that simple

5. dont have "website.com/admin/"

6. dont use "UPDATE" or "INSERT" or "DELETE" querys

7. etc.

*nearly, unless you get slashdotted i suppose, then i expect your server will go down before the left (random) half also provides a collision anyway :-)

Stupid comment

....as it's asychronous and a malicious user could write data back to your database if implemented incorrectly."

The fact that it is asychronous has absolutely nothing at all to do with whether or not it has the ability to write back to the database.

You can have AJAX calls that write to the database, and ones that don't, both being asychronous. Also you can have sychronous AJAX calls (is this just "JAX"???) that write to the database.

Anyway - its pretty much the same considerations you should take when writing any web application. Verify all inputs, period.

Network security 101

If a functionality is remotelly available via a public network then anybody can try to hack into your system via it.

Without AJAX: A web application serves pages via single HTTP calls, possibly with one or more parameters, per page.
- Hackers can try getting into your system via this web application by tweaking the parameters, URL, HTTP headers, etc of the requests used to retrive pages

With AJAX: A web application serves pages via a single HTTP call, possible with one or more parameters, per page. Additionaly, JavaScript embedded in the page will, typically in response to user input, send extra HTTP requests to get more information (mostly in XML or plain text format).
- Hackers can try getting into your system via this web application by tweaking the parameters, URL, HTTP headers, etc of the requests used to retrive pages or extra information.

Same principle for both, it's just that with AJAX there is a bigger number of entry points (more "handlers" for HTTP requests) since asynchronous HTTP requests from the Javascript code also require server-side code to process those requests (and generate responses).

Can you trust that nobody will try to get into your system by hand-executing an HTTP Request to a request handler that's supposed to only be called by Javascript code? Of course not!

It's the same reason why when an HTTP form is submited to the server you still check (on the server side) the validity of the information submited for that form even though your Javascript validator also does a full validation of the form before allowing the user to submit it.

Programmers that don't implement checks on information submited to the server and/or feed it directly to interpreted language engines (such as SQL query executers) without escaping or protecting it (in some other way) will ALWAYS leave gaping security holes open, AJAX or no AJAX.

An incompetent programmer is always an incompetent programmer.

buzzword wins, flawless victory

In Mortal Kombat 2, A JAX fatility showed a large African American man rip the arms off his enemy.

"AJAX" alternative?

Can somebody please come up with a name other than AJAX? I find myself talking about the programming techniques covered by the moniker of "AJAX" (herein after refered to as "BLURG") and wanting to call it something other than "AJAX":

BLURG is not necessarily asynchronous: you may be updating only a small part of the page, but doing it synchronously.

BLURG does not require XML. In fact you could be returning HTML, Javascript, CSV, JSON, etc.

BLURG does not even require the XmlHttpRequest feature and BLURG techniques have been in use far before the existance of this feature.

Can we please come up with a better name for BLURG, one that covers the more general programing techniques involved? Something for us people to use that is NOT just the trendy new thing known as AJAX? Something that we can use that will let others like us know that we have been aware of these techniques even before the term AJAX was coined?

For now I will call it BLURG...

Cross site request forgery

It seems that the author is unaware of all the research that has already been done in this area. This type of attack is known as Cross-site request forgery [wikipedia.org] and the counter-measures (which the author re-derives from first principles in his article) are already known.

Most secure AJAX app evah

- JavaScript is used to create an SQL query based on what report the user wants.
- This SQL string is submitted in a form and executed as an SQL query directly without any checks or anything.
- The db user executing the query has enough rights to read / edit / delete all databases on the server.
- Everything the query returns is serialised and passed back to JavaScript to parse and display.

That's an actual case in an actual web application, though the guy had long experience with SQL he was new with AJAX apps, so we caught that in the code audit.

Now he knows that's a Really Bad Idea to do, I wonder how many boys and girls out there don't.

I'm pretty sure...

...that my AJAX-based Slashdot posting console is secure.

But most of all, samy is my hero [namb.la].

all of my servlets

.. check for the session to be correct.. in other words, a user must login first and that login is stored in the session. so any of my servlets that actually talk to my database need that login first, as they ALL check the session. You can't just post the form to do an update in my system, you must have other data in order for that post to actually pass step 1. This is IN every servlet.

AJAX like all JS should be supplimental at best

We design applications so that they function entirely with JS disabled. All data that is validated on the front end is re-validated on the backend along with session state verification. If you aren't doing this you are going to get what you deserve in the end.

depends on which 'side' you are on

"...and a malicious user could write data back to your database if implemented incorrectly."

Isn't that supposed to be, "...if implemented correctly"

Validation

Always validate what you run through eval()!

While not fool proof, making sure that what you got back from the server is JSON, and not a string of malicious code is paramount.

And guess what, such things already exist [json.org].

Granted, this doesn't prevent someone from embedding that same malicious code in valid object code that appears identical to what you expect as a server result, but its a huge step in the right direction.

I have to say, stupid stupid stupid

Browser.... request .... security .... application
Browser.... asynch request .... security .... application

erm, questions?

The point has nothing to do with 'asynch' but more to do with programmers think that the average user cannot produce requests to these server objects easily, despite being simple http calls...

so there. all bollocks.

code to learn, right.

The only decent thing said in the article is right below the big 'darknet.org.uk' logo.
I totally agree about that.