What the...

IPFuscation is a technique that allows for IP addresses to be represented in hexadecimal, octal, or a combination, instead of the decimal encoding that we are used to.

What can we do?

Normal: ping 45.54.123.21

Hexadecimal + Decimal + Octal: ping 0x2d.54.123.025

Hexadecimal: ping 0x2d367b15

Hexadecimal with period symbol: ping 0x2d.0x36.0x7b.0x15

Hexadecimal with 0 padding: ping 0x0000000002d.0x00000000036.0x00000007b.0x0000000015

Decimal: ping 758545173

Octal: ping 05515475425

Octal with period symbol: ping 055.066.0173.025

Octal with 0 padding: ping 000000055.000066.000000173.0000000025

As we can see there's a bunch of ways you can ping the same IP. For a moment, I wondered if this was just how Ping worked. However, given that this works with OpenURL, I decided to try it with Cobalt Strike!

GitHub

I wrote a script that automatically outputs a set of known formats for the same IP address that you specify. Hopefully will be useful for some people!

​https://github.com/vysecurity/IPFuscator​

Usage

python .\ipfuscator.py 127.0.0.1
IPFuscator
Author: Vincent Yiu (@vysecurity)
https://www.github.com/vysec/IPFuscator
Version: 0.1.0
​
IP Address:     127.0.0.1
​
Decimal:        2130706433
Hexadecimal:    0x7f000001
Octal:          017700000001
​
Full Hex:       0x7f.0x0.0x0.0x1
Full Oct:       0177.0.0.01
​
Random Padding:
Hex:    0x000000000000000007f.0x00000000000000000000.0x0000000000000000000.0x0000000000000000000001
Oct:    0000000000000000000000000177.000000000000000.0000000000000000000000.0000000000000000000000000000001
Random base:
#1:     0x7f.0x0.0.1
#2:     127.0.0x0.0x1
#3:     0177.0x0.0.1
#4:     0x7f.0.0.1
#5:     127.0x0.0x0.1
​
Random base with random padding:
#1:     0x0000000007f.0.0000000000.00000000000001
#2:     0x000000000007f.0x0000000000000000000000.0x00000000000000.0x00000000001
#3:     00000000000000000000000177.0x00000000.000000000000000.00000000000000000000000001
#4:     000000000000000177.0.0.1
#5:     127.0000000000000000000000.00000000000000.0x0000000000001

Cobalt Strike

Although I rarely use IP addresses compared to hostnames when it comes to connecting to resources, we know for a fact that many threat actors do. In some cases you may want to resort to using IP addresses and this technique can add a bit of flavor to the mix.

To use this technique in Cobalt Strike, you simply create a listener like you normally would. Let's say my IP was 45.54.123.21, run IPFuscator as shown below:

You can immediately take this information and use any of these representations in your listener address. For example: ​

Generate a payload as you would normally, and it all works fantastically!

You could even mix it up a bit:

Cobalt Strike Aggressor Script

I actually wrote a Cobalt Strike Aggressor Script to automatically convert an IP that you can issue with the ping command that will convert and use ping with a hexadecimal equivalent IP. If you want to use this you can obtain this script in my Aggressor repository. This was released back in 2017.

Conclusion

IPFuscation is not an advanced technique. However, it can be used to:

1. potentially break regex rules for command line logging looking for IP addresses. Eg. when you issue a command such as ping 0055.0x0036.000173.0x0015

2. obfuscate previously unobfuscated / unencrypted cleartext strings to C2 locations within the payload

According to inphosys on Reddit, the proxy sees the regular decimal IP address notation:

To keep it simple, make the use of IPs cool again! :)