Archive for the ‘security’ Category

Re-evaluating how some actions are performed can sometimes lead to new insights, which is exactly the reason for this blog post. Be aware that I’ve only tested this on two ‘test’ networks, so I cannot guarantee this will always work. Worst scenario you’ll read an (hopefully) out-of-the-box blog entry about an alternative port scan method that maybe only works in weird corner cases. The source for the script can be found on my gist, if you prefer to skip my ramblings and jump directly to the source.

One of the things I usually do is sniff traffic on the network that I am connected to with either my laptop or a drop device. At that point the output of the ifconfig command usually looks similar to this:

 eth0 Link encap:Ethernet HWaddr 00:0c:29:4b:e7:35 
 inet6 addr: fe80::20c:29ff:fe4b:e735/64 Scope:Link
 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
 RX packets:386316 errors:0 dropped:0 overruns:0 frame:0
 TX packets:25286 errors:0 dropped:0 overruns:0 carrier:0
 collisions:0 txqueuelen:1000 
 RX bytes:390745367 (390.7 MB) TX bytes:4178071 (4.1 MB)

Like you will notice the interface has no IPv4 IP address assigned, you can ignore the IPv6 address for now. Normally I determine which IP address or MAC address to clone based on the traffic that I captured and analysed previously. Then I’m all set to start port scanning or performing other type of attacks.

This time however I wondered what type of activities I could perform without an IP address. I mean it would be pretty interesting to talk IP to devices, somehow see a response and not be traceable, right? So I decided to see if it would for example be possible to perform a port scan on the network without having an IP address configured on my network interface.

Since usually when you want to perform non-standard, weird or nifty tricks with TCP/IP you have to resort to raw sockets I decided to directly jump to scapy to build a POC. My working theory was as follow:

Normally when I am just sniffing traffic I see all kind of traffic that gets send to the broadcast address, so what if we perform a port scan and we specify the broadcast address as the source?

I decided to test this using two virtual machine (ubuntu & Windows 10) with the network settings on ‘NAT’ and also tested with the same virtual machines while bridged to a physical network. The following oneliners can be used to transmit the raw packet:

pkt = Ether(dst='00:0c:29:f6:a5:65',src='00:08:19:2c:e0:15') / IP(dst='172.16.218.178',src='172.16.218.255') / TCP(dport=445,flags='S')
sendp(pkt,iface='eth0')

Running tcpdump will confirm if this works or not, moment of truth:

tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size 262144 bytes
23:27:21.903583 IP (tos 0x0, ttl 64, id 1, offset 0, flags [none], proto TCP (6), length 40)
 172.16.218.255.20 > 172.16.218.178.445: Flags [S], cksum 0x803e (correct), seq 0, win 8192, length 0
23:27:21.904440 IP (tos 0x0, ttl 128, id 31823, offset 0, flags [DF], proto TCP (6), length 44)
 172.16.218.178.445 > 172.16.218.255.20: Flags [S.], cksum 0x03be (correct), seq 3699222724, ack 1, win 65392, options [mss 1460], length 0
23:27:24.910050 IP (tos 0x0, ttl 128, id 31824, offset 0, flags [DF], proto TCP (6), length 44)
 172.16.218.178.445 > 172.16.218.255.20: Flags [S.], cksum 0x03be (correct), seq 3699222724, ack 1, win 65392, options [mss 1460], length 0
23:27:30.911092 IP (tos 0x0, ttl 128, id 31825, offset 0, flags [DF], proto TCP (6), length 44)
 172.16.218.178.445 > 172.16.218.255.20: Flags [S.], cksum 0x03be (correct), seq 3699222724, ack 1, win 65392, options [mss 1460], length 0
23:27:42.911498 IP (tos 0x0, ttl 128, id 31829, offset 0, flags [DF], proto TCP (6), length 40)
 172.16.218.178.445 > 172.16.218.255.20: Flags [R], cksum 0x1af8 (correct), seq 3699222725, win 0, length 0

wOOOOOOOt!! It seems to work. We can clearly see the packet being sent to the ‘.178’ IP address from the broadcast (.255) source address and then we see the response flowing back to the broadcast address.

Now that’s pretty interesting right? Essentially we can now perform port scans without being really traceable on the network. Somehow this still feels ‘weirdish’ because it just works on first try…so still thinking I missed something :/

sudo ./ipless-scan.py 172.16.218.178 00:0c:29:f6:a5:65 -p 445 3389 5000 -i eth0
2017-10-26 23:13:33,559 - INFO - Started ipless port scan
2017-10-26 23:13:33,559 - INFO - Started sniffer and waiting 10s
2017-10-26 23:13:43,568 - INFO - Starting port scan
2017-10-26 23:13:43,604 - INFO - Found open port - 445
2017-10-26 23:13:43,628 - INFO - Found open port - 3389
2017-10-26 23:13:43,645 - INFO - Found closed port - 5000
2017-10-26 23:13:43,654 - INFO - Finished port scan, waiting 5s for packets
2017-10-26 23:13:52,626 - INFO - Stopped sniffer
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A good periodic reminder when attempting to learn things is that reading about the subject is not the same as actually practicing the subject you read about. That is why it’s always a good thing to practice what you have read. In this case we are going to dive into the well known Java deserialization bugs that have been around for a while now. The best part of practicing it is that you get to really know the subject at hand and can attempt to improve upon it for your own needs. For this blog post we are going to attempt the following:

  1. Exploit a deserialization bug
  2. Manually create our payload

So to clarify, step one will be about practicing the exploitation of a serialization bug with current tools as well as explaining the approach taken. The second step zooms in on the payload; what exactly is the payload? How can we construct it by hand? With the end result of fully understanding how it works as well as having an approach to understand similar bugs in the future.

I’ll mention all tools used throughout the blog post, but at the very least you’ll need the following:

That is the bug we will be exploiting. The reason for choosing a simulated bug is the fact that we can control all aspects of it and thus better understand how a deserialization exploit really works.

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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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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

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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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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