There are a ton of ways to brute force login forms, you just need to google for it and the first couple of hits will usually do it. That is of course unless you have Burp in which case it will be sufficient for most of the forms out there. Sometimes however it will not be so straight forward and you’ll need to write your own tool(s) for it. This can be for a variety of reasons, but usually it boils down to either a custom protocol over HTTP(S) or some custom encryption of the data entered. In this post we are going to look at two ways of writing these tools:

  • Your own python script
  • A Greasemonkey script

Since to write both tools you first need to understand and analyse the non-default login form let’s do the analysis part first. If you want to follow along you’ll need the following tools:

  • Python
  • Burp free edition
  • Firefox with the Greasemonkey plugin
  • FoxyProxy
  • FireFox developer tools (F12)

Please note that even though we are using some commercially available software as an example, this is NOT a vulnerability in the software itself. Most login forms can be brute forced, some forms slower than others ;) As usual you can also skip the blog post and directly download the python script & the Greasemonkey script. Please keep in mind that they might need to be adjusted for your own needs.

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By now everyone has probably heard of Quantum Insert NSA style, if you haven’t then I’d recommend to check out some articles at the end of this post. For those who have been around for a while the technique is not new of course and there have been multiple tools in the past that implemented this type of attack. The tools enabled you to for example fully hijack a telnet connection to insert your own commands, terminate existing connections or just generally mess around with the connection. Most of the tools relied on the fact that they could intercept traffic on the local network and then forge the TCP/IP sequence numbers (long gone are the days that you could just predict them).

So it seems this type of attack, in which knowing the sequences numbers aids in forging a spoofed packet, has been used in two very specific manners:

  • Old Skool on local networks to inject into TCP streams
  • NSA style by globally monitoring connections and injecting packets

There is a third option however that hasn’t been explored yet as far as i know, which is using this technique to bypass IP filters for bi-directional communication. You might wonder when this might come in handy right? After all most of the attackers are used to either directly exfiltrate through HTTPS or in a worst case scenario fall back to good old DNS. These methods however don’t cover some of the more isolated hosts that you sometimes encounter during an assignment.

During a couple of assignments I encountered multiple hosts which were shielded by a network firewall only allowing certain IP addresses to or from the box. The following diagram depicts the situation:

As you can see in the above diagram, for some reason the owner of the box had decided that communication with internet was needed, but only to certain IP addresses. This got me thinking on how I could exfiltrate information. The easiest way was of course to exfiltrate the information in the same way that I had obtained access to the box, which was through SSH and password reuse. I didn’t identify any other methods of exfiltration during the assignment. This was of course not the most ideal way out, since it required passing the information through multiple infected hops in the network which could attract some attention from the people in charge of defending the network.

A more elegant way in my opinion would have been to directly exfiltrate from the machine itself and avoid having a continuous connection to the machine from within the network. In this post we are going to explore the solution I found for this challenge, which is to repurpose the well known quantum insert technique to attempt and build a bi-directional communication channel with spoofed IP addresses to be able to exfiltrate from these type of isolated hosts. If you are thinking ‘this only works if IP filtering or anti address spoofing is not enforced’ then you are right. So besides the on going DDOS attacks, this is yet another reason to block outgoing spoofed packets.

If you are already familiar with IP spoofing, forging packets and quantum insert you can also skip the rest of this post and jump directly to QIBA – A quantum insert backdoor POC. Please be aware that I only tested this in a lab setup, no guarantees on real world usage :)

Lastly as you are probably used to by now, the code illustrates the concept and proofs it works, but it’s nowhere near ready for production usage.

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The last couple of days there has been some fuzz about the HP audio key logger as disclosed by modzero in their blog post and the detailed advisory that they released. The following sentence in their advisory peeked my interest:

This type of debugging turns the audio driver effectively into a keylogging spyware.

With all the hyped ‘repurposing’ of tools that is going on lately I wondered how difficult it actually is to turn this into an intended piece of malware. The reason I find this interesting is because according to different sources it’s legitimate software which has been code-signed correctly and has not been classified as malware by all anti-virus solutions, yet.

https://www.virustotal.com/nl/file/e882149c43976dfadb2746eb2d75a73f0be5aa193623b18b50827f43cce3ed84/analysis/

https://www.virustotal.com/nl/file/c046c7f364b42388bb392874129da555d9c688dced3ac1d6a1c6b01df29ea7a8/analysis/

The current detection signatures are also pretty weak since they deem it mostly ‘riskware’  or ‘potentially unwanted application (PUA)’. This could have the side effect that users or administrators might just dismiss any warnings of signs of an attacker abusing the HP audio key logger for malicious purposes.

For red team purposes this is still a nice addition, since it pushes the person analysing this potential incident to really understand what is going on and figuring out that legitimate software is being abused for malicious purposes. Specially since the binary will not be modified and thus the code-signing remains valid (until the certificate is revoked).

Let’s dive into the technical details on the path / approach I followed on repurposing this piece of legitimate software for nefarious red team purposes ;)

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Even though we are pretty used to it, libpcap is not always present on systems. Usually, regardless of your goal, looking at traffic is actually pretty useful. In my experience this applies to offensive (pentesting, red team) work as well as defensive (incident response, network monitoring) work.

One of the first things that comes to mind, when libpcap is not available, is of course raw sockets, since these seem to be always available as long as you have the correct privileges. I’ve written previously about them as well as created some POC for backdoor purposes. Up until now raw sockets haven’t failed me, so when during a recent assignment I had to sniff traffic without libpcap I decided to write some Python code to achieve this. In case you are wondering, yes this was to further gather juicy information from unencrypted protocols like telnet, http and ftp.

A script nowadays never starts without a quick google query to save yourself the trouble of writing everything from scratch. So even though I enjoy writing a lot of things from scratch to learn, in this case I mainly adjusted an excellent example script from: http://askldjd.com/2014/01/15/a-reasonably-fast-python-ip-sniffer/

Adjusting the above script to save the data in pcap format was an easy undertaking and immediately useful. After waiting for a couple of minutes I got myself a nice pcap file which I could analyse on another machine with regular tools like tcpdump or wireshark.

You can find the script on the following gist

Quick blog to remind myself what the correct combination of options are to run Windows 10 Pro x64 with secure boot enabled within VMWare Fusion. Couple of reason why you’d want to do this:

  • Avoid a secondary dedicated laptop
    • Avoid having a physical TPM chip
  • Get familiar with Hyper-V
  • Better understand and research secure boot
  • Get more familiar with memory analysis on hypervisor memory
  • Just for fun

Fusion settings

  • Enable EFI by adding the following to the ‘.vmx’ file
    • firmware = “efi”
  • Enable VT-x/EPT
    • can be found in setting under “Processors & Memory”, “advanced settings”
  • Choose OS type “Hyper-V (unsupported)”

Windows 10 Pro x64 (host) settings

  • Right click on the windows start menu icon and select
    • Programs and Features
      • Turn Windows features on or off
    • Select the Hyper-V role
  • Using the Hyper-V Manager create a “Generation 2” VM
    • In Settings -> Security check the “Enable Trusted Platform Module” checkbox
  • When booting hold down a key or it won’t detect the installation ISO

Windows 10 Pro x64 (guest) settings

  • Right click on the C drive and select “Enable bitlocker”
  • Add a second hard disk and create a folder on it to save the bitlocker recovery key

References

 

So this is a quick post with hopefully the goal of saving somebody else some time. Just for the record, I could have missed something totally trivial and I will hopefully get corrected :)

When working with the registry_persistence module, it turns out that one of the registry entries turns into garbage. At first I blamed myself of course, but it turned out that this could probably be a bug in the meterpreter code of which I’m not sure if it really is a bug or if there is a new API call which I haven’t found yet. So when executing the module the registry looks like this:

registry_garbled

Like you can see that’s not exactly how it really should look like, since what we are expecting is something more human readable and an actual powershell command.

The quick work around is to generate the correct string with the correct encoding and for me it was easier to do this with python:

a = "%COMSPEC% /b /c start /b /min powershell -nop -w hidden -c \"sleep 1; iex([System.Text.Encoding]::Unicode.GetString([System.Convert]::FromBase64String((Get-Item 'HKCU:myregkey_name').GetValue('myregkey_value'))))\""
b = '\\x'.join("{:02x}".format(ord(c)) for c in a.encode('UTF-16LE'))
print '\\x' + b

You can then just hard code the output string into the module (replace the original ‘cmd=’ string with your hex encoded one like cmd=”\x25\x00″ etc) and it should appear correctly in your registry. Following screenshot shows before and after:

registry_fixed

If you are curious how you could debug similar bugs yourself, keep on reading for a short tour of the problem solving part. If you are wondering why I don’t submit a PR to metasploit, that’s cause unicode scares the **** out of me. My usual experience is I generate more problems when dealing with unicode than I intended to fix.

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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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