Member Avatar for shwick

I'm trying to set up a secure ftp transfer between my linux machine and my internet gateway running ubuntu 8.04.

I have vsftpd installed but I can't get PASV connection to work with putty. My ubuntu firewall blocks everything except ssh.

From my windows XP machine I establish a connection with putty to my ubuntu machine. I have putty forward local port 21(windows machine) to 127.0.0.1:21(ubuntu machine).

This works sort of. I use the ftp client from windows command line to connect to 127.0.0.1 21, which forwards me to port 21 on the ubuntu machine and allows me to connect/login.

Then after I enter "quote PASV" and try a "dir" command it hangs. In vsftpd.conf I had added lines pasv_max_port=21 and pasv_min_port=21 so that the ftp server would tell the windows ftp client to use port 21 for data transfers.

I then added "pasv_address=127.0.0.1" to vsftpd.conf, thinking vsftp was telling the windows ftp client to try and connect to something other than localhost, and vsftpd wouldn't start, it said I had to edit 2 files.

I already have sftp working with psftp.exe, but I'd like one entry point into my system and psftp doesn't load bash.bashrc, so I want ftp through ssh to work.

See this site for PASV ftp: http://www.slacksite.com/other/ftp.html

# Example config file /etc/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.
#
#
# Run standalone?  vsftpd can run either from an inetd or as a standalone
# daemon started from an initscript.
listen=YES
#
# Run standalone with IPv6?
# Like the listen parameter, except vsftpd will listen on an IPv6 socket
# instead of an IPv4 one. This parameter and the listen parameter are mutually
# exclusive.
#listen_ipv6=YES
#
# Allow anonymous FTP? (Beware - allowed by default if you comment this out).
anonymous_enable=NO
#
# Uncomment this to allow local users to log in.
local_enable=YES
#
# Uncomment this to enable any form of FTP write command.
write_enable=YES
pasv_max_port=21
pasv_min_port=21
pasv_address="127.0.0.1"
#
# 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.
#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/vsftpd.log
#
# If you want, you can have your log file in standard ftpd xferlog format
#xferlog_std_format=YES
log_ftp_protocol=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 blah FTP 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 restrict local users to their home directories.  See the FAQ for
# the possible risks in this before using chroot_local_user or
# chroot_list_enable below.
#chroot_local_user=YES
#
# 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().
#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
#
#
# Debian customization
#
# Some of vsftpd's settings don't fit the Debian filesystem layout by
# default.  These settings are more Debian-friendly.
#
# This option should be the name of a directory which is empty.  Also, the
# directory should not be writable by the ftp user. This directory is used
# as a secure chroot() jail at times vsftpd does not require filesystem
# access.
secure_chroot_dir=/var/run/vsftpd
#
# This string is the name of the PAM service vsftpd will use.
pam_service_name=vsftpd
#
# This option specifies the location of the RSA certificate to use for SSL
# encrypted connections.
rsa_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
# This option specifies the location of the RSA key to use for SSL
# encrypted connections.
rsa_private_key_file=/etc/ssl/private/ssl-cert-snakeoil.key
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  • Latest Post Latest Post by gaowei

Dani AI

Generated

— the control channel (port 21) is being forwarded over SSH, but passive FTP opens a separate data connection to whatever IP:port the server advertises. Forwarding only port 21 will never carry those PASV data connections, and if the PASV range is invalid vsftpd will fall back to ephemeral ports (which is why Wireshark showed high-numbered ports).

Corrective steps:

  • Ensure the passive range is valid (min < max) and pick a contiguous high port range. For example:
    pasv_min_port=55000
pasv_max_port=55100
  • Open that entire range in iptables/ufw and, if the server is behind NAT, forward the same range on the router to the FTP host.
  • Set pasv_address to the IP/hostname that clients actually connect to (the public IP for internet clients; 127.0.0.1 only if the client is truly connecting to the local loop via SSH forwarding). Use pasv_addr_resolve=YES if a hostname is used. connect_from_port_20 only affects active mode, not passive.

Options and workarounds:

  • Tunnel the whole PASV range over SSH (multiple forwarded ports in PuTTY) or use dynamic (SOCKS) forwarding and an FTP client that supports SOCKS/proxies (Windows ftp.exe does not).
  • Prefer SFTP (the SSH File Transfer Protocol) when using SSH: it avoids PASV/active issues entirely and uses the single SSH connection (psftp/WinSCP/ FileZilla SFTP).

Quick troubleshooting checklist:

  • Confirm vsftpd started cleanly and check logs (syslog/vsftpd) for errors.
  • Use netstat -lntp or ss -lntp to see which ports vsftpd is listening on and run a packet capture to verify the server-advertised PASV port.
  • If the PASV port seen on the wire is outside the intended range, recheck the min/max ordering and restart vsftpd.

— PuTTY is fine for SSH; the FTP PASV behavior is independent of PuTTY itself.

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Member Avatar for shwick

Ok I decided to ditch the port forwarding and just get it working normally first. I got it working by opening my local interface through iptables.

In vsftpd.conf I specified a port range of 55000 to 55100 for PASV ports, but vsftpd doesn't use that range.

Using wireshark I captured ftp packets and saw vsftpd sent PASV ports 62237 and 58847 for two different ftp sessions.

Why is it not using the specified range?


Here is a non-commented copy of vsftpd.conf.

listen=YES
anonymous_enable=NO
local_enable=YES
write_enable=YES
pasv_max_port=55000
pasv_min_port=55100
dirmessage_enable=YES
xferlog_enable=YES
connect_from_port_20=YES
log_ftp_protocol=YES
secure_chroot_dir=/var/run/vsftpd
pam_service_name=vsftpd
rsa_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
rsa_private_key_file=/etc/ssl/private/ssl-cert-snakeoil.key

Member Avatar for gaowei

I use putty in my school's laboratory.
But I don't know you how to use vsftp?
Thanks!

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