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FTPS (comúnmente referido como FTP/SSL) es un nombre usado para abarcar un número de formas en las cuales el software FTP puede realizar transferencias de ficheros seguras. Cada forma conlleva el uso de una capa SSL/TLS debajo del protocolo estándar FTP para cifrar los canales de control y/o datos. No debe confundirse con el protocolo seguro de transferencia de ficheros SFTP, el cual suele ser usado con SSH.

Instalar vfstpd

# Centos
yum install vsftpd
# Ubuntu / Debian
apt-get install vsftpd

Comprobar que el binario de vsftpd server instalado tiene soporte para SSL

ldd /usr/sbin/vsftpd | grep -i ssl
        libssl.so.10 => /lib64/libssl.so.10 (0x00007f124f64b000)

Crear el certificado SSL + llave privada (/etc/vsftpd/vsftpd.pem)

openssl req -x509 -nodes -days 9999 -newkey rsa:20148 -keyout /etc/vsftpd/vsftpd.pem -out /etc/vsftpd/vsftpd.pem

Creación de usuario local (sin shell) y la carpeta donde se subirán descargarán documentos (/home/USUARIO/files).

useradd USUARIO
passwd USUARIO
usermod -s /sbin/nologin USUARIO
chmod a-w /home/USUARIO/
mkdir /home/USUARIO/files
chown USUARIO:USUARIO /home/USUARIO/files

La configuración dada anteriormente ayudará a prevenir este error cuando se tiene la opción “allow_writeable_chroot” activa en vsftpd.

500 OOPS: vsftpd: refusing to run with writable root inside chroot ()

En CentOS puede ser aconsejable desctivar SELinux (/etc/selinux/config) y configurar o desactivar el firewall

# CentOS 7
systemctl disable firewalld
systemctl enable vsftpd

Configuración de vsftpd (/etc/vsftpd/vsftpd.conf)

vsftpd.conf

# The default compiled in settings are fairly paranoid. This sample file
# loosens things up a bit, to make the ftp daemon more usable.
# Please see vsftpd.conf.5 for all compiled in defaults.
#
# READ THIS: This example file is NOT an exhaustive list of vsftpd options.
# Please read the vsftpd.conf.5 manual page to get a full idea of vsftpd's
# capabilities.
#
# Allow anonymous FTP? (Beware - allowed by default if you comment this out).
anonymous_enable=NO
#
# Uncomment this to allow local users to log in.
# When SELinux is enforcing check for SE bool ftp_home_dir
local_enable=YES
#
# Uncomment this to enable any form of FTP write command.
write_enable=YES
#
# Default umask for local users is 077. You may wish to change this to 022,
# if your users expect that (022 is used by most other ftpd's)
local_umask=022
#
# Uncomment this to allow the anonymous FTP user to upload files. This only
# has an effect if the above global write enable is activated. Also, you will
# obviously need to create a directory writable by the FTP user.
# When SELinux is enforcing check for SE bool allow_ftpd_anon_write, allow_ftpd_full_access
#anon_upload_enable=YES
#
# Uncomment this if you want the anonymous FTP user to be able to create
# new directories.
#anon_mkdir_write_enable=YES
#
# Activate directory messages - messages given to remote users when they
# go into a certain directory.
dirmessage_enable=YES
#
# Activate logging of uploads/downloads.
xferlog_enable=YES
#
# Make sure PORT transfer connections originate from port 20 (ftp-data).
connect_from_port_20=YES
#
# If you want, you can arrange for uploaded anonymous files to be owned by
# a different user. Note! Using "root" for uploaded files is not
# recommended!
#chown_uploads=YES
#chown_username=whoever
#
# You may override where the log file goes if you like. The default is shown
# below.
xferlog_file=/var/log/xferlog
#
# If you want, you can have your log file in standard ftpd xferlog format.
# Note that the default log file location is /var/log/xferlog in this case.
xferlog_std_format=YES
#
# You may change the default value for timing out an idle session.
#idle_session_timeout=600
#
# You may change the default value for timing out a data connection.
#data_connection_timeout=120
#
# It is recommended that you define on your system a unique user which the
# ftp server can use as a totally isolated and unprivileged user.
#nopriv_user=ftpsecure
#
# Enable this and the server will recognise asynchronous ABOR requests. Not
# recommended for security (the code is non-trivial). Not enabling it,
# however, may confuse older FTP clients.
#async_abor_enable=YES
#
# By default the server will pretend to allow ASCII mode but in fact ignore
# the request. Turn on the below options to have the server actually do ASCII
# mangling on files when in ASCII mode.
# Beware that on some FTP servers, ASCII support allows a denial of service
# attack (DoS) via the command "SIZE /big/file" in ASCII mode. vsftpd
# predicted this attack and has always been safe, reporting the size of the
# raw file.
# ASCII mangling is a horrible feature of the protocol.
#ascii_upload_enable=YES
#ascii_download_enable=YES
#
# You may fully customise the login banner string:
ftpd_banner=Welcome to Vagrant Basebox SFTP service.
#
# You may specify a file of disallowed anonymous e-mail addresses. Apparently
# useful for combatting certain DoS attacks.
#deny_email_enable=YES
# (default follows)
#banned_email_file=/etc/vsftpd/banned_emails
#
# You may specify an explicit list of local users to chroot() to their home
# directory. If chroot_local_user is YES, then this list becomes a list of
# users to NOT chroot().
# (Warning! chroot'ing can be very dangerous. If using chroot, make sure that
# the user does not have write access to the top level directory within the
# chroot)
chroot_local_user=YES
#chroot_list_enable=YES
# (default follows)
#chroot_list_file=/etc/vsftpd/chroot_list
#
# You may activate the "-R" option to the builtin ls. This is disabled by
# default to avoid remote users being able to cause excessive I/O on large
# sites. However, some broken FTP clients such as "ncftp" and "mirror" assume
# the presence of the "-R" option, so there is a strong case for enabling it.
ls_recurse_enable=YES
#
# When "listen" directive is enabled, vsftpd runs in standalone mode and
# listens on IPv4 sockets. This directive cannot be used in conjunction
# with the listen_ipv6 directive.
listen=YES
#
# This directive enables listening on IPv6 sockets. By default, listening
# on the IPv6 "any" address (::) will accept connections from both IPv6
# and IPv4 clients. It is not necessary to listen on *both* IPv4 and IPv6
# sockets. If you want that (perhaps because you want to listen on specific
# addresses) then you must run two copies of vsftpd with two configuration
# files.
# Make sure, that one of the listen options is commented !!
listen_ipv6=NO
 
pam_service_name=vsftpd
userlist_enable=YES
tcp_wrappers=YES
 
# FTPS
ssl_enable=YES
allow_anon_ssl=YES
force_local_data_ssl=NO
force_local_logins_ssl=NO
ssl_tlsv1=YES
ssl_sslv2=NO
ssl_sslv3=NO
rsa_cert_file=/etc/vsftpd/vsftpd.pem
rsa_private_key_file=/etc/vsftpd/vsftpd.pem
require_ssl_reuse=NO
ssl_ciphers=HIGH

Con las directivas siguientes permitimos también el acceso FTP normal sin obligar al uso de TLS/SSL.

force_local_data_ssl=NO
force_local_logins_ssl=NO

Comprobar los logs del servicio vsftpd server en CentOS 7 (systemd)

journalctl -u vsftpd.service

Solución al problema: warning: can't get client address: Socket operation on non-socket.

# Alguna directiva "listen" debe estar activada o bien el puerto desocupado para su uso.
listen=YES

Conectar con el programa coreFTP al servicio FTPS: Connection “Connection AUTH TLS”.