Tricking blind Java deserialization for a treat

During a black-box penetration test we encountered a Java web application which presented us with a login screen. Even though we managed to bypass the authentication mechanism, there was not much we could do. The attack surface was still pretty small, there were only a few things we could tamper with.

1. Identifying the entry point

In the login page I noticed a hidden POST parameter that was being sent for every login request:

<input type="hidden" name="com.ibm.faces.PARAM" value="rO0..." />

The famous Base64 rO0 (ac ed in HEX) confirmed us that we were dealing with a Base64 encoded Java serialized object. The Java object was actually an unencrypted JSF ViewState. Since deserialization vulnerabilities are notorious for their trickiness, I started messing with it.

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Robot hacking research

Later this past month, our lab welcomed a very important individual: Robi the robot (it has a camera and speakers!). We also received the honors to assemble it and make it dance. And so the journey to the fields of the unknown started. While playing with the command and control software, I could not help but wonder how secure this really is.

First of all, from the start I expected some kind of bluetooth link (blueborne *cough cough*) but I was actually greeted with it’s very own WiFi network board . It has the capability to join an existing network but by default it also comes with an open AP with a suggestive SSID. From the start, I also encountered a defense mechanism which is defined by allowing only a single C&C connection to be established with another machine.

By further inspecting the C&C mobile software, I saw the IP address which confirmed to be the gateway/WiFi manager interface. After a quick scan, the identified number of open ports:

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Going further with Responder’s Basic Authentication

There are a good number of situations when we find ourselves abusing the LLMNR and NBT-NS protocols on an infrastructure penetration test, more specifically on an Active Directory setup. These 2 protocols are enabled by default on most of the Windows operating systems. What are they doing is they facilitate the communication between network machines when searching for a DNS hostname regardless if it’s a share, a server or a web hostname.

The overview picture of the attack vector:

  • the victim is looking for a non-existing hostname
  • the DNS server cannot resolve the request
  • we reply and resolve the hostname resolution query
  • we ask the victim for authentication

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Exploiting Timed Based RCE

Checking the timeIn a recent penetration testing project we encountered a situation where in order to prove exploitability and possible damage we had to exfiltrate data from an isolated server using an OS command injection time based attack.

The scope of the project was an API. During the testing process we identified an interesting GET request that received 2 parameters: the first  a string and the other one ID number.

By fuzzing the string parameter, at first, it looked like we had a potential SQL injection, based on the way it handled single quotes. Trying this attack vector didn’t seem successful, but when we sent the ` sleep  10` command and the HTTP response returned 10 seconds later, we knew we had something.  Our first thought was that this was game over for the application, we managed to get a Remote Code Execution on the API server.

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Practical JSONP Injection

JSONP injection is a lesser known but quite widespread and dangerous vulnerability and it surfaced in the last years due to the high rate of adoption of JSON, web APIs and the urging need for cross-domain communications.

What is JSONP?

Assuming everybody knows what JSON is, let’s talk a little about JSONP. JSONP comes from JSON with Padding and it was created in order to bypass common restrictions such as Same-origin Policy which is enforced for XMLHttpRequest (AJAX requests).

Let’s take an example. Our online banking application, http://verysecurebank.ro, has implemented an API call that returns the current user’s transactions.

An HTTP request to the http://verysecurebank.ro/getAccountTransactions endpoint presents us with the transactions, JSON formatted:

json-transactions

If our reports application, accessible at http://reports.verysecurebank.ro wants to get the transaction details, an AJAX call to the page won’t be possible, due to Same-origin Policy being in effect (different host).

sop-json

To get around this problem, JSONP came into play. Since Cross-domain script inclusion (mostly used to externally load JavaScript libraries such as jQuery, AngularJS etc.) is allowed, but not recommended, a smart trick apparently solved the entire equation: prepending the response with a callback.

Note: even if it might be obvious, it’s worth mentioning that when including a script cross-domain, it will run in the context of the including application, not in the source’s context.

Adding a callback to the API response, wrapped around the JSON formatted data, allows us to load the API response between script tags and get its content by defining our own callback function to handle it.

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