Monthly Archives: August 2016

Fun with Frida


August 22, 2016

During a previous engagement Securus Global was asked to review a desktop application that used a local SQLite3 database to store a list of blacklisted URLs. As expected the database file was encrypted and not much that could be done with the database.

If the consultant tried to open the database using any SQLite3 client an error message would pop up in our face. At Securus Global we have extensive experience with Frida, a framework that allows you to inject JavaScript to explore native apps on Windows, Mac, Linux, iOS and Android (more on Frida here http://frida.re). It is used heavily in our Mobile App Penetration Tests so the team decided to take a further look at the application and managed to trace the “requests” to libsqlite3.dylib.

Keep in mind that the same approach will work for libsqlite3.so. Also note that this has not been tested in a Windows environment.

Our goal at the time was to discover the SQL queries performed by the application and try to acquire some useful information, we started to look into two specific functions in libsqlite3.dylib:

The open function is defined as: Continue reading

Bypassing PHP Null Byte Injection protections – Part II – CTF Write-up


August 19, 2016

Update: Below is a list of people who solved the CTF. Congrats folks!

  • Dixie Flatline
  • AhnMo
  • Cernica Ionut
  • jinmo123
  • noproto
  • perzik
  • XeR
  • Rev
  • mphx2
  • [ace]
  • menztrual
  • simon
  • Dario D. Goddin

Overview

This post is the second part of the Bypassing PHP Null Byte injection protections blogpost. If you want to try the CTF first before going through the write up, head to the link first. Otherwise, keep on reading :)

The main trick described in this write-up relies on the fact that a Local File Include (LFI) vulnerability is exploitable but with some restrictions imposed by the code. Among these restrictions, there is some active filtering on Path Traversal. Name;u, an image file extension (.png) is always appended to the successfully uploaded files. In addition, the server is running an up to date version of PHP which is not vulnerable to the well known Null Byte Injection trick.

To bypass these restrictions and successfully achieve Remote Code Execution chaining through the aforementioned LFI vulnerability, one can use one of the built-in PHP Wrappers as described in detail on the next section of this write-up.

Description

When visiting the URL of the vulnerable application one can see that it is a web app for uploading pictures:

 

Following the normal application flow first, I tried to understand how the application behaves and how the uploaded files are being parsed by the code with some simple tests:

Continue reading

Bypassing PHP Null Byte Injection protections


August 15, 2016

Overview

The Null Byte Injection is pretty old vulnerability. As an example, this post from 1996(!) describes the same problem affecting CGI scripts. Yet, this vulnerability still bites now and then.

PHP suffered from this issue for quite a long time and was not fixed until late December 2010 when the final fix was implemented in version 5.3.4.

All is not lost and there are some other tricks out there which allows you to overcome this fix and still exploit Local File Include (LFI) vulnerabilities. For this reason, we thought it would be beneficial for  the community to come up with a CTF challenge followed by a write-up on the tricks which are not entirely spread out on the Interwebs.

My friend and Securus Global co-worker Márcio challenged me to try the CTF challenge that he came up with recently. The challenge aims to present a not widely known technique used to bypass some common file upload restrictions imposed on PHP applications. Restrictions, that prevent unauthorized upload of files to the web server using web application.

Here is the link to the challenge: http://198.199.84.56

I’ll spoil the fun a little bit and tempt you to try it out: The challenge is all about cute Pandas. ☺

Enjoy!

Simple MySQL Backdoor using User Defined Functions (UDF)


August 10, 2016

So what is a UDF? It is a way to extend MySQL with a new function that works like a native (built-in) MySQL function; i.e., by using a UDF you can create native code to be executed on the server from inside MySQL. To do this you need to write a library (shared object in Linux, or DLL in Windows), put it into a system directory, then create the functions in MySQL. Usually people write UDFs using C/C++, but you can really use any language you want since you are creating a shared object. This has the advantage of being simple to write while also being highly portable.  The real benefit is that you don’t need to access or modify the source code of MySQL, and after the UDF is installed you can update the DBMS without the need to make any changes to your code (i.e., it is transparent).

Continue reading

Are Padding Oracles still a concern?


August 05, 2016

The very fact this article came to be implies the answer – yes, they are. Readers who are interested in knowing the rationale behind this statement are encouraged to continue reading.

The main motivation behind writing this article was a padding oracle vulnerability (CVE-2016-2107) found on May 2016 in a popular OpenSSL cryptographic toolkit. Authors of this article decided that it is a great occasion to revisit this area and to refresh information about the padding oracles.

In 1998 Daniel Bleichenbacher first demonstrated a practical adaptive chosen-ciphertext attack. Four years later in 2002 Serge Vaudenay presented the very first practical padding oracle attack. Since that time notable vulnerabilities belonging to this category were also discovered, e.g. CVE-2013-0169 (Lucky13) and CVE-2014-3566 (POODLE), to name the most recognized ones.
After some time, some people even started to believe that this type of attack is no longer a problem (i.e. no longer considered a threat in real-life). Despite this and similar opinions, we can observe that new padding oracle vulnerabilities are continuously discovered by security researchers and 14 years after the first practical attack was presented, they still pose a very real security threat.

What is padding oracle? What can happen if someone finds this vulnerability in my application and will be able to exploit it? How can I test, identify and avoid this type of attack? Let’s address these and other questions in the following sections.

Refresher

First things first. Let’s refresh on what the padding oracle attack is. The definition according to MITRE states:

“An attacker is able to efficiently decrypt data without knowing the decryption key if a target system leaks data on whether or not a padding error happened while decrypting the ciphertext.

In addition to performing decryption, an attacker is also able to produce valid ciphertexts
(i.e., perform encryption) by using the padding oracle, all without knowing the encryption key”.

Source: https://capec.mitre.org/data/definitions/463.html

For readers who would like to refresh information about the padding oracles, please refer to the following materials:

Continue reading