CryptoApi Derandomization

In this post I dig a bit into the Windows's CryptoApi library, trying to locate the code that the library uses to fill buffers with random data when it needs to randomize something (i.e. paddings for plaintexts at RSA encryption, randomly generated AES keys, etc...). After locating the interesting functions, I wrote a PoC that I share in this post and that intercepts that functions to disable CryptoApi randomization to have deterministic ciphering results. Finally,  I do a quick reversing on an OrcaKiller sample (it uses CryptoApi), disabling CryptoApi's randomization to make the analysis easy.

Installation and First Contact With the New WinDbg

These days it is being my first contact with the new Windbg. There are fantastic things in this new version, I am still discovering and enjoying it. I decided to write this short post about the particular installation of the new WinDbg and the way that I needed to configure VirtualKD’s vmmon to attach the new WinDbg to the selected running VM from the vmmon menu.

Using Gathering Information Tools Through TOR Network

Previous days I have been playing with nmap and other tools to gather information, through tor network. I wanted to share my experience with it, and the configuration that I am currently using. I hope you can find here some tips or ideas useful for you.

Tools For Unpacking Malware, Part 2. Weak encryption algorithms

Some days ago I started a series of posts about tools and methods for unpacking malware, here you can find the first part. Each malware/packer is very different, and sometimes there are no generic ways to unpack them. But sometimes we can find characteristics shared by a number of them. For example, packers usually rely on weak encryption algorithms and, sometimes, it is possible to attack them.

Tools For Unpacking Malware, Part 1. Dumping executables from RWE memory

This is the first part of a series of articles (at least I will write a second part and i hope to continue) where I will write about different ways that I use to unpack malware, and where I will share some tools and scripts that I use frequently for this purpose. I hope these articles and tools will be useful for you.

Anti-Antidebugging WinDbg Scripts

In this post I would like to share some scripts for WinDbg that they were useful for me while I was reversing malware with antidebug tricks. In the future I would like to write additional scripts related to this issue, and I will update this post to have all together. I hope these scripts will be useful for you too.

Analysis of PoSeidon downloader and keylogger

In this post I analyze a sample of Poseidon (sample: 1b7f205b663af9a6eb44f18555bdaad86e0fa58f3a9e4aced3e2ae1e3ed472b5, you can read about it here). The original sample is a downloader. It is working, and there are online and working CnCs in the list of CnCs that the sample carries. However the malware could be failing to download the second stage executable (the keylogger) because of a bug in the downloader.

Analysis of new variant of Konni RAT

These days TalosIntelligence commented about a new variant of Konni RAT. It is not a complicated malware, but it implements some interesting tricks and functionality typical of RATs. I wanted to take a look at something different (there is more life after the ransomware  ) and in this post you can find a brief analysis of this RAT. I hope you enjoy it.

Petya ransomware + EternalBlue

In this short post i want to share a first quick reversing of petya+eternalblue dll, md5: 3936bda83b590512fa2cfef8acf6c294. It is a first look at it, i hope the information here it is correct.

Loading and Debugging Windows Kernel Shellcodes with Windbg. Debugging DoublePulsar Shellcode

In this article i’d like to share a windbg script that will let us to load a shellcode from a file to kernel memory and create a kernel thread to execute it. I have not played a lot with the script yet, if you find some bug please tell me.

Analysis of .Net malware: ransomware SamSam

SamSam is a ransomware that is written in C#. It’s not an interesting malware, it hasn’t new interesting features or tricks to comment, however I wanted to write a post about the tools that I use to analyze .Net malware since long time ago, and this was a good opportunity to do it.

Monero Coin Mining Malware

Lately, while reviewing and classifying samples, I have been seeing an increase in CoinMiners, specially CoinMiners oriented to mine Monero virtual coin. For this reason I decided to write a short article about virtual coin mining and this kind of malware.

Analyzing ATM malware

Since a time ago, they are beginning to appear a new wave of malware targeting Automated Teller Machines (ATM): Backdoor.MSIL.Tyupkin, Backdoor.Padpin, the newer GreenDispenser, etc… All of them seem to be using the eXtensions for Financial Services (XFS) library to manage ATM. If you try to debug/analyze or you introduce a sample of these malware families into a Cuckoo sandbox, it won’t run because it will fail to load msxfs.dll.

Batch, attach and patch: using windbg’s local kernel debugger to execute code in windows kernel

In this article I am going to describe a way to execute code in windows kernel by using windbg local kernel debugging. It’s not a vulnerability, I am going to use only windbg’s legal functionality, and I am going to use only a batch file (not powershell, or vbs, an old style batch only) and some Microsoft’s signed executables (some of them that are already in the system and windbg, that we will be dumped from the batch file).

Analysis of the ransom/infector W32_VirRnsm.A

There are lot of ransomware families around the world, however, since long time ago, they contain no new interesting features. VirRnsm.A is a malware that mixes characteristics of ransomwares and infectors. It is a ransomware capable to infect executable files (or an infector capable to encrypt your files). Technically, It doesn’t seem a great malware, but it is worth a look because, from my point of view, in the future we are going to start to see a lot of malwares of this type. Ransomware’s behaviour could end up being a payload of worms and infectors, rather than a malware by itself.

Debugging programs with multiple processes with windbg’s kernel mode debugger

It’s common to reverse malware (or any type of software) that creates multiple processes or loads drivers, and it is useful to be able to debug the new created processes or loaded drivers from entry point.

Debugging BSOD when trying to delete malformed registry key on Windows 8.1

The last days my computer started to crash suddenly, with bug check 0x51 (REGISTRY_ERROR). It was totally random, so i decided to analyze the crash. I decided to write an article about this because, in spite of the fact that it doesn’t seem a security problem, i learnt some interesting things about windows registry.

Microsoft Office Compatibility Pack tries to execute path without quotes

A couple of days ago i found a weird behaviour in my computer. When i double-clicked a .docx file, an error message appeared saying c:\Program couldn’t be executed. I don’t know when and why i had an empty file named “c:\Program” on my computer (i had been doing tests with %PROGRAMFILES% envar in my code and i guess the file derived of this).

I investigated a bit about it and it seems to be a bug of the “Microsoft Office Compatibility Pack for Word, Excel, and PowerPoint File Formats”. It seems it keeps into a registry key a path to wordconv.exe without quotes, so when svchost.exe tries to execute c:\Program files\Microsoft office\Office12\Wordconv.exe, if c:\Program exists in the machine, it executes c:\Program.

Getting CryptoWall and CryptoDefense working without C&C

It's common to find malware samples that need the C&C to work. This is the case of Cryptowall and CryptoDefense ransomwares. If you need to debug samples of these families you will usually find the C&C down and the ransom won't work and won't encrypt files. It only will try to connect to C&C continuously.

In this article i'm going to describe a way to create a fake C&C for CryptoWall and CryptoDefense families, and how to get samples of these families working into a vmware for example.