20, 21 - FTP

REFERENCES
FTP Commands	See here
FTP Status Codes	See here

PRIMARY CATEGORY → PROTOCOLS AND SERVICES

FTP → File Transfer Protocol

Ports

• 20 → Data Channel

This data channel is used exclusively for data transmission in Active FTP Mode

IMPORTANT

In Passive FTP Mode, the client initiates the connection, from a random port to a FTP Server’ dynamic port, which has been previously indicated to the client by the FTP Server

Therefore, Port 20 is not used in this TCP/IP connection

• 21 → Control Channel

The client and server stablish the first TCP/IP through this port

Furthermore, this Control Channel is used by the client to send all the FTP Commands, such as put, get or dir to the FTP server

Modes

• Active

The client previously indicates in the Control Channel which destination port the FTP Server should use to stablish the connection to the client itself

Thus, in Active FTP Mode, the FTP Server initiates the connection from its 20 Port to the port previously indicated by the client

• Passive

In this case, is the FTP Server that tells the client which port to connect to on the server itself

In this mode, the client initiates the Data Channel connection from a random port to the dynamic port specified in the Control Channel by the FTP Server

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Enumeration

User Authentication

FTP Client

ftp <TARGET> [PORT]
> USER
> PASSWORD

Web Browser

ftp://<USERNAME>:<PASSWORD>@<TARGET>:[PORT]

Anonymous Login

ftp -a <TARGET> [PORT]

The -a option bypasses the normal login procedure and use anonymous login instead

Banner Grabbing

Netcat

nc -nv <TARGET> <PORT> <<< ""

TLS Certificate

OpenSSL

openssl s_client -connect <TARGET>:<PORT> -starttls ftp

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Download Files Recursively

Passive Mode

wget --mirror "ftp://anonymous:anonymous@<TARGET>"

Active Mode

wget --mirror --no-passive-ftp "ftp://anonymous:anonymous@<TARGET>"

Special Chars in Credentials

wget --mirror [--no-passive-ftp] --user '<USER>' --password '<PASSWORD>' "ftp://<TARGET>"

wget --mirror [--no-passive-ftp] --ftp-user='<USER>' --ftp-password='<PASSWORD>' "ftp://<TARGET>"