Silky-CTF: 0x01: Vulnhub Walkthrough

Today we will be solving a boot2root lab from Vulnhub called SILKY-1. This lab, like many others, is a good way to keep your penetration testing skills sharp while getting some variety.

Download it from here: https://www.vulnhub.com/series/silky-ctf,207/

Level : Easy-Intermidate

Task: Boot to Root (flag.txt)

Penetration Methodologies

Scanning

·         Netdiscover

·         Nmap

Enumeration

·         Web Spreading

·         Robots.txt

·         Generating Password Dictionary (Crunch)

Exploit

·         Brute force attack (Hydra)

·         SSH Login

Identify SUID Enable Binaries

·         Privilege Escalation

·         Exploit PATH Variable

Capture the flag

WALKTHROUGH

Scanning

We start by scanning the network for targets using Netdiscover.

netdiscover

So we found target IP 192.168.1.106 and proceed by running a Nmap scan for all its ports to see what we can find.

nmap  -A 192.168.1.106

Since port 8080 is running HTTP-proxy, so our obvious choice is to browse Target’s IP in the browser but didn’t found any hint.

Enumeration

We checked the robots.txt file for the results of nmap and showed /notes.txt as our next indication.

So, we found a text message that is written in German when we explored the notes.txt file.

With the help of Google translator, I translate the German message, which was connected to password hint:

“I absolutely have to remove the password from the page, after all, the last 2 characters are missing. But still.”

Then again, I visit the home page to view its source code and found a link for script.js

So, I found the word: s1lKy when navigate to /script.js as shown below.  Hmmm!!! This word s1lKy could be the possible password as said in the above text message.

So, without wasting time I decided to generate a dictionary with the help of crunch. As per the text message last 2 character are missing. But these 2 characters could be any combination such as alpha-alpha, alpha-ALPHA, alph-numeric, alpha-special character or vice-versa and so on.

And after spending almost one-an-hour I successfully found the valid combination for ssh login as port 22 is opened.

crunch 7 7 -t s1lky^% >> pass.txt

Exploit

Assuming username could be silky, and password could be in pass.txt, I lunched brute force attack using hydra on port 22 for identifying valid combination of ssh login.

hydra -l silky -P pass.txt 192.168.1.106 ssh

Since we found silky:s1lky#5 as username and password for ssh login, now its was time to access ssh shell and escalated the root privilege to capture the flag.

ssh silky@192.168.1.106

Once I logged in successfully then without wasting much time, I looked for SUID enabled binaries and here /usr/bin/sky looks interesting.

find / -perm -u=s -type f 2>/dev/null

Although when I run this program it shown “root” in its output as result along with some German text. To analysis its result I try to inspect the program script with the help of strings which a command line utility to identify file type.

stings /usr/bin/sky

Hmm!! the information I found through strings was that, this program is executing to commands simultaneously. First echo command to show the German text message and another whoami.

Privilege Escalation

To escalated root privilege, we can abuse PATH Variable as shown below and for more detail read complete article from here.

echo ‘/bin/sh’ > whoami

chmod 777 whoami

export PATH=/tmp:$PATH

/usr/bin/sky

OKAY!! We got another shell which is a root shell as shown below, let’s now grab the flag.txt file and complete the challenge.

id

cd /root

flag.txt