I’ll give an example. At my previous company there was a program where you basically select a start date, select an end date, select the system and press a button and it reaches out to a database and pulls all the data following that matches those parameters. The horrors of this were 1. The queries were hard coded.
-
They were stored in a configuration file, in xml format.
-
The queries were not 1 entry. It was 4, a start, the part between start date and end date, the part between end date and system and then the end part. All of these were then concatenated in the program intermixed with variables.
-
This was then sent to the server as pure sql, no orm.
-
Here’s my favorite part. You obviously don’t want anyone modifying the configuration file so they encrypted it. Now I know what you’re thinking at some point you probably will need to modify or add to the configuration so you store an unencrypted version in a secure location. Nope! The program had the ability to encrypt and decrypt but there were no visible buttons to access those functions. The program was written in winforms. You had to open the program in visual studio, manually expand the size of the window(locked size in regular use) and that shows the buttons. Now run the program in debug. Press the decrypt button. DO NOT EXIT THE PROGRAM! Edit the file in a text editor. Save file. Press the encrypt button. Copy the encrypted file to any other location on your computer. Close the program. Manually email the encrypted file to anybody using the file.
Java webapp. Customer facing. E-commerce application, so in PCI scope and dealt with credit card info and such.
There was one specific cookie that stored some site-wide preference for the customer. (Why not just put that preference in the database associated with the user? Because that would make too much sense is why.)
But the way they encoded the data to go into the cookie? Take the data, use the Java serialization framework (which is like Python’s “Pickle” or Go’s “Gob”) to turn that into a string. But that string has binary data in it and raw binary data is kindof weird to put in a cookie, so you base64 encode the result. (The base64 encoding was the only sane step in the whole process.) Then you do the reverse when you receive the cookie back from the browser. (And no, there was no signature check or anything.)
The thing about the Java serialization framework, though is that decoding back into Java objects runs arbitrary object constructors and such. As in, arbitrary code execution. And there’s no checking in the deserialization part of the Java serialization framework until your code tries to cast the object to whatever type you’re expecting. And by that point, the arbitrary code execution has already happened. In short, this left a gaping vulnerability that could easily have been used to extremely ill effect, like a payment information breach or some such.
So all a malicious user had to do to run arbitrary code on our application server was serialize something, base64 encode it, and then send it to our servers as a cookie value. (Insert nail biting here.)
When we found out that there was a severe vulnerability, I got the task of closing the hole. But the existing cookies had to continue to be honored. The boss wasn’t ok with just not honoring the old cookies and developing a new cookie format that didn’t involve the Java serialization framework.
So I went and learned enough about the internal workings of how the Java serialization framework turned a Java value into a binary blob to write custom code that worked for only the subset of the Java serialization format that we absolutely needed for this use case and no more. And my custom code did not allow for arbitrary code execution. It was weird and gross and I made sure to leave a great big comment talking about why we’d do such a thing. But it closed the vulnerability while still honoring all the existing cookies, making it so that customers didn’t lose the preference they’d set. I was proud of it, even though it was weird and gross.
The value that was serialized to put into the cookie? A single Java int. Not a big POJO of any sort. Just a single solitary integer. They could just as well have “serialized” it using base-10 rather than using the Java serialization framework plus base64.
Some minecraft mods had/have a similar problem. They use javas serialization stuff for sending stuff between client and server. There is mod that partially fixes this by only allowing whitelisted classes to be deserialized.
Gson in the corner murdered:
Wow… If you can answer was this like a single company or were you selling the service to other companies?
If selling to multiple companies did you offer a “new” version and a “security patch” for the old or just made everyone use your implementation?
This was a developed-in-house e-commerce web application at a major e-retailer. So fortunately that monstrosity of a cookie-handling mess was only ever used by one company.
You know what, though? Talking about this reminds me of another story about the same e-commerce application.
After a customer placed an order on this e-commerce site, the company’s fraud department had to evaluate the order to make sure it wasn’t fraudulently placed. (As in, with a credit card not owned or authorized for use by the purchaser.) Once that was done, the order had to be communicated to a worker at the warehouse so they could pack the right items into a box, put on a shipping label, and set the box aside to be picked up by the UPS truck which would come once a day near the end of the day.
The application used by the fraud department and the application that displayed new orders to warehouse workers was one and the same application. Whether a user had fraud-evaluating powers or pack-items-in-boxes powers just depended on what permissions their particular user had. (That may have been decided by LDAP groups. I don’t remember for sure.)
Meanwhile, the e-commerce site offered gift cards for sale online. The gift card would be shipped to the customer. And there was a box where you could write a message associated with the gift card. So, for instance, someone could buy a gift card to be sent to their nephew’s address or whatever and include a little note like “Happy Birthday. Don’t spend it all at once.” or whatever. And the fraud/pick-and-pack application would display all details of the order including any messages associated with the gift cards.
Well, I found a stored cross-site scripting vulnerability where if you put
<script>...</script>tags with some JavaScript in the gift card message box and completed the order, the JavaScript would execute any time someone viewed the details page for the order in the fraud/pick-and-pack application. And of course, the JavaScript could do within that application just about anything the user could do with their given permissions.The main danger was that a malicious actor with sufficient knowledge of how our fraud application worked could place an order fraudulently with someone else’s credit card and include in the order a gift card with a malicious JavaScript payload in the message box, and then that malicious JavaScript could automatically mark the order “a-ok, no fraud here” when a fraud department worker loaded the order details page, letting the order be fulfilled without any actual fraud review.
The fix was pretty simple. Just stick a
<c:out>...</c:out>in the appropriate place in the fraud/pick-and-pack application code. But it was an interesting example of a vulnerability in a not-customer-facing application that could none-the-less be exploited by any public customer/user without any particular special access.If you’re interested in one more interesting story about the same e-commerce application, see this comment I made a while ago.
That is interesting, I dealt with purely internal software so never considered that.