windows

Intro to Mimikatz

One of the most interesting tools in a penetration tester’s arsenal is mimikatz.  Mimikatz is a tool that scrapes the memory of the process responsible for Windows authentication(LSASS) and reveals cleartext passwords and NTLM hashes that an attacker can use to pivot around a network.  From that point they escalate privilege either by authenticating with the clear text credentials or passing the hash. Sounds deadly right? Most people have the reaction “Why hasn’t Microsoft come up with a solution to this?”.

If you Google the phrase “defending against mimikatz” the information you find is a bit lackluster. The best article I have found was this one. It has a lot of good suggestions like using the “Protected Users” group(SID: S-1-5-21-<domain>-525) available in recent versions of Active Directory and also limiting administrator usage, and taking advantage of not storing passwords in memory with a registry setting. You can limit the number of services running as system or remove debug privilege to help prevent an attacker from being able to run mimikatz. What this and other articles make you believe is that you need to have Windows 8 or 8.1 or 10 rolled out everywhere. What about the large number of Windows 7/2008 R2 machines out there? Well it turns out you can defend against mimikatz on these versions of Windows, here is how. Read Full Article

I love SSH, coupled with byobu(an updated GNU screen) it is amazingly powerful.  But sometimes it is really useful to be able to view a GUI application on the remote server end.  Some people think that they need to use VNC to do this.  VNC is terrible, and there is a better way.

Things you will need:

  • An X capable SSH client
    • On Linux you don’t have to worry about this
    • On Windows I recommend MobaXTerm
    • On OS X I think you just need to install something like XQuartz
  • A server that has a graphical environment installed on it
    • Ubuntu Desktop is an easy example
    • Gnome/KDE/XFCE/X11 etc.
  • SSH server installed on the server
  • A GUI application that you want to run over SSH

In my example I’m going to be connecting from a Windows computer, using MobaXTerm, to a Ubuntu Desktop machine, and running WireShark(yes I know about tshark).

Make sure sshd is installed on the Ubuntu machine.

$ sudo apt-get install ssh

Back on the Windows machine, we SSH to the Ubuntu machine. Notice that we are specifying -X which allows us to run X applications over SSH

$ ssh -X username@192.168.1.100

Then we run our application

$ wireshark

And there you have it:
WiresharkOverX

That is Wireshark running on the remote Linux machine.  Notice the GTK/Ubuntu looking buttons, and the Windows colored Window frame.

Thanks for stopping by!

Photo Credit

Intro

Most IT people are somewhat familiar with Wireshark.  It is a traffic analyzer, that helps you learn how networking works, diagnose problems and much more.

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One of the problems with the way Wireshark works is that it can’t easily analyze encrypted traffic, like TLS.  It used to be if you had the private key(s) you could feed them into Wireshark and it would decrypt the traffic on the fly, but it only worked when using RSA for the key exchange mechanism.  As people have started to embrace forward secrecy this broke, as having the private key is no longer enough derive the actual session key used to decrypt the data.  The other problem with this is that a private key should not or can not leave the client, server, or HSM it is in.  This lead me to coming up with very contrived ways of man-in-the-middling myself to decrypt the traffic(e.g. sslstrip or mitmproxy).

Session Key Logging to the Rescue!

Well my friends I’m here to tell you that there is an easier way!  It turns out that Firefox and Chrome both support logging the symmetric session key used to encrypt TLS traffic to a file.  You can then point Wireshark at said file and presto! decrypted TLS traffic.  Read on to learn how to set this up. Read Full Article