Archive for the ‘general’ Category

So after a period of ‘lesser technical times’ I finally  got a chance to play around with bits, bytes and other subjects of the information security world.  A while back I got involved in a forensic investigation and participated with the team to answer the investigative questions.  This was an interesting journey since a lot of things peeked my interest or ended up on one of my todo lists.

One of the reasons that my interest was peeked is that yes, you can use a lot of pre-made tools to process the disk images and after that processing is done you can start your investigation. However, there are still a lot of questions you could answer much quicker if you had a subset of that data available ‘instantly’. The other reason is that not all the tools understand all the filesystems out there, which means that if you encounter an exotic file system your options are heavily reduced. One of the tools I like and which inspired me for these quick & dirty scripts is ‘mac-robber‘ (be aware that it changes file times if the destination is not mounted read-only) since it’s able to process any file system as long as it’s mounted on an operating system on which mac-robber is able to run. An example of running mac-robber:

sudo mac-robber mnt/ | head
class|host|start_time
body|devm|1471229762
MD5|name|inode|mode_as_string|UID|GID|size|atime|mtime|ctime|crtime
0|mnt/.disk|0|dr-xr-xr-x|0|0|2048|1461191363|1461191353|1461191353|0
0|mnt/.disk/base_installable|0|-r–r–r–|0|0|0|1461191363|1461191316|1461191316|0
0|mnt/.disk/casper-uuid-generic|0|-r–r–r–|0|0|37|1461191363|1461191353|1461191353|0

You can even timeline the output if you want with mactime:

sudo mac-robber mnt/ | mactime -d | head
Date,Size,Type,Mode,UID,GID,Meta,File Name
Thu Jan 01 1970 01:00:00,2048,…b,dr-xr-xr-x,0,0,0,”mnt/.disk”
Thu Jan 01 1970 01:00:00,0,…b,-r–r–r–,0,0,0,”mnt/.disk/base_installable”
Thu Jan 01 1970 01:00:00,37,…b,-r–r–r–,0,0,0,”mnt/.disk/casper-uuid-generic”
Thu Jan 01 1970 01:00:00,15,…b,-r–r–r–,0,0,0,”mnt/.disk/cd_type”
Thu Jan 01 1970 01:00:00,60,…b,-r–r–r–,0,0,0,”mnt/.disk/info”

Now that’s pretty useful and quick! One of the things I missed however was the ability to quickly extend the tools as well as focus on just files. From a penetration testing perspective I find files much more interesting in an forensic investigation than directories and their meta-data. This is of course tied to the type of investigation you are doing, the goal of the investigation and the questions you need answered.

I decided to write a mac-robber(ish) python version to aid me in future investigations as well as learning a thing or two along the way. Before you continue reading please be aware that:

  1. The scripts have not gone through extensive testing
  2. Thus should not be blindly trusted to produce forensically sound output
  3. The regular ‘professional’ tools are not perfect either and still contain bugs ;)

That being said, let’s have a look at the type of questions you can answer with a limited set of data and how that could be done with custom written tools. If you don’t care about my ramblings, just access the Github repo here. It has become a bit of a long article, so here are the ‘chapters’ that you will encounter:

  1. What data do we want?
  2. How do we get the data?
  3. Working with the data, answering questions
    1. Converting to body file format
    2. Finding duplicate hashes
    3. Permission issues
    4. Entropy / file type issues
  4. Final thoughts

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Errr ok, so the “NSA-style content searching” might be a bit overrated then again it’s usually only the intelligence agencies which perform this type of bulk searches as far as I know. Anyhow, here is an idea on how to abuse Google DLP (available in google apps for work) to perform exactly the same, since it recently incorporated support to also perform OCR on the emails / attachments:

According to this screenshot it seems that you can also perform DLP actions on incoming items:

google-dlp

Which is what enables us to perform specific content searches on all incoming email messages and prepend  certain keywords to the subject. Now imagine you just hacked an organisation and added a rule to the exchange server or individual outlook instances to forward all email to an email your control and has DLP enabled with all the keywords, hashes or rules you need to only get the juicy contents out? Don’t forget to delete the forwarded message with a rule ;) The types of content matching that you can perform is also pretty flexible:

  • Pattern match—A specific alphanumeric pattern (not just string length), including delimiters, valid position, and valid range checks
  • Context—Presence of relevant strings in proximity to pattern and/or checksum matching string
  • Checksum—Checksum computation and verification with check digit
  • Word/phrase list—Full or partial match to an entry found in a dictionary of words and phrases

Based on the DLP trigger you can then just rename the subject and use google rules to forward the message to another inbox or leave it there and just organise it into folders. Kinda saves you as an attacker a lot of time, since normally you’d have to perform or implement OCR / content matching yourself. Added bonus is that since it’s already been stolen from the victim company it doesn’t really matter what you do with it as long as the original sender doesn’t receive some weird Google notification.

You might be thinking “my client will never allow this”, but what if your client is already connected to google apps for work?

As a final thought you could also use this for defence purposes if you are already working with Google apps for work as an organisation. You could use the Google DLP feature to feed it the currently hyped ‘threat intelligence’ file hash information and block different known threat actors if their tools & techniques remain the same for a period of time.

PowerShell overview and introduction

Posted: February 6, 2016 in general
Tags:

This is a long overdue post I was planning on writing as a reference for myself, since I don’t write that much PowerShell. Depending on your own knowledge about powershell you can just skip to whatever sections seems useful to you. Also feel free to correct any mistakes in this article since I intent it mostly as a basic reference :) The resource section contains a nice collection of links to other PowerShell articles & tools, which means you can consider this article a small recap of all the resources linked.

TL;DR The resource section contains useful URLs to learn Power Shell, the blog post itself is just a micro-recap of those resources.

  • What is PowerShell and why would you use it?
  • Basic PowerShell environment
  • How do you run PowerShell?
  • What is the PowerShell syntax?
  • Our first script
  • Calling Windows functions
  • Resources

basic-powershell-commands-intro-840x420

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Well this will be a rather short post since it’s about the automation of my previous blog post in which we analysed the memory dump of the pageant process and manually extracted unencrypted keys. You can find the tool which automates this process in pageant_xkeys git repository. Since I’m a firm believer that you learn best from mistakes and old code, the repository also includes some of the other code I was playing around with.

 

A Red Team exercise is lotsa fun not only because you have a more realistic engagement due to the broader scope, but also because you can encounter situations which you normally wouldn’t on a regular narrow scoped penetration test. I’m going to focus on pageant which Slurpgeit recently encountered during one of these red team exercises which peeked my interest.

Apparantly he got access to a machine on which the user used pageant to manage ssh keys and authenticate to servers without having to type his key password every single time he connects. This of course raises the following interesting (or silly) question:

Why does the user only have to type his ssh key in once?

Which has a rather logical (or doh) answer as well:

The pageant process keeps the decrypted key in memory so that you can use them without having to type the decryption password every time you want to use the key.

From an attackers perspective it of course begs the question if you can steal these unencrypted keys? Assuming you are able to make a memory dump of the running process you should be able to get these decrypted ssh keys. During this blog post I’ll be focusing on how you could achieve this and the pitfalls I encountered when approaching this.

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Implementing functionality that is already available in an available tool is something that has always taught me a lot, thus I keep on doing it when I encounter something I want to fully understand. In this case it concerns the ‘hiberfil.sys’ file on Windows. As usual I first stumbled upon the issue and started writing scripts to later find out someone had written a nice article about it, which you can read here (1). For the sake of completeness I’m going to repeat some of the information in that article and hopefully expand upon it, I mean it’d be nice if I could use this entry as a reference page in the future for when I stumble again upon hibernation files. Our goal for today is going to be to answer the following question:

What’s a hiberfil.sys file, does it have slack space and if so how do we find and analyze it?

To answer that question will hopefully be answered in the following paragraphs; we are going to look at the hibernation process, hibernation file, it’s file format structure, how to interpret it and finally analyze the found slack space. As usual you can skip the post and go directly to the code.

Hibernation process

When you put your computer to ‘sleep’ there are actually several ways in which it can be performed by the operating  system one of those being the hibernation one. The hibernation process puts the contents of your memory into the hiberfil.sys file so that the state of all your running applications is preserved. By default when you enable hibernation the hiberfil.sys is created and filled with zeros. To enable hibernation you can run the following command in an elevated command shell:

powercfg.exe -H on

If you want to also control the size you can do:

powercfg.exe -H -Size 100

An interesting fact to note is that Windows 7 sets the size of the hibernation file size to 75% of your memory size by default. According to Microsoft documentation (2) this means that hibernation process could fail if it’s not able to compress the memory contents to fit in the hibernation file. This of course is useful information since it indicates that the contest of the hibernation file is compressed which usually will make basic analysis like ‘strings’ pretty useless.

if you use strings always go for ‘strings -a <inputfile>’ read this post if you are wondering why.

The hibernation file usually resides in the root directory of the system drive, but it’s not fixed. If an administrators wants to change the location he can do so by editing the following registry key as explained by this (3) msdn article:

Key Name: HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management\
Value Name: PagingFiles
Type: REG_MULT_SZ
Data: C:\pagefile.sys 150 500
In the Data field, change the path and file name of the pagefile, along with the minimum and maximum file size values (in megabytes).

So if you are performing an incident response or forensic investigation make sure you check this registry key before you draw any conclusion if the hiberfil.sys file is absent from it’s default location. Same goes for creating memory images using hibernation, make sure you get the 100% and write it to a location which doesn’t destroy evidence or where the evidence has already been collected.

Where does the slack space come from you might ask? That’s an interesting question since you would assume that each time the computer goes into hibernation mode it would create a new hiberfil.sys file, but it doesn’t. Instead it will overwrite the current file with the contents it wants to save. This is what causes slack space, since if the new data is smaller in size than the already available files the data at the end of the file will still be available even if it’s not referenced by the new headers written to the file.

From a forensic standpoint that’s pretty interesting since the unreferenced but available data might contain important information to help the investigation along. If you are working with tools that automatically import / parse or analyse the hiberfil.sys file you should check / ask / test how they handle slack space. In a best case scenario they will inform you about the slack space and try to recover the information, in a less ideal scenario they will inform you that there is slack space but it’s not able to handle the data and in the worst case scenario it will just silently ignore that data and tell you the hibernation file has been processed successfully.

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We all know that sqlmap is a really great tool which has a lot of options that you can tweak and adjust to exploit the SQLi vuln you just found (or that sqlmap found for you). On rare occasions however you might want to just have a small and simple script or you just want to learn how to do it yourself. So let’s see how you could write your own script to exploit a blind SQLi vulnerability. Just to make sure we are all on the same page, here is the blind SQLi definition from OWASP:

Blind SQL (Structured Query Language) injection is a type of SQL Injection attack that asks the database true or false questions and determines the answer based on the applications response.

You can also roughly divide the exploiting techniques in two categories (like owasp does) namely:

  • content based
    • The page output tells you if the query was successful or not
  • time based
    • Based on a time delay you can determine if your query was successful or not

Of course you have dozens of variations on the above two techniques, I wrote about one such variation a while ago. For this script we are going to just focus on the basics of the mentioned techniques, if you are more interested in knowing how to find SQLi vulnerabilities you could read my article on Solving RogueCoder’s SQLi challenge. Since we are only focusing on automating a blind sql injection, we will not be building functionality to find SQL injections.

Before we even think about sending SQL queries to the servers, let’s first setup the vulnerable environment and try to be a bit realistic about it. Normally this means that you at least have to login, keep your session and then inject. In some cases you might even have to take into account CSRF tokens which depending on the implementation, means you have to parse some HTML before you can send the request. This will however be out of scope for this blog entry. If you want to know how you could parse HTML with python you could take a look at my credential scavenger entry.

If you just want the scripts you can find them in the example_bsqli_scripts repository on my github, since this is an entry on how you could write your own scripts all the values are hard coded in the script.

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