Iptables – Failed to retrieve directory listing in Filezilla connecting to vsftpd

centos6ftpiptablesvsftpd

newbie here.

At first I was unable to connect to vsftpd but I added port 21 in iptables (i'm running on Centos 6) and managed to make it work. But now, I can't get past Command: LIST in Filezilla

Here is the log:

Status: Connecting to 162.xxx.xx.xxx:21...
Status: Connection established, waiting for welcome message...
Response:   220 (vsFTPd 2.2.2)
Command:    USER cjflores
Response:   331 Please specify the password.
Command:    PASS ******************
Response:   230 Login successful.
Command:    OPTS UTF8 ON
Response:   200 Always in UTF8 mode.
Status: Connected
Status: Retrieving directory listing...
Command:    PWD
Response:   257 "/"
Command:    TYPE I
Response:   200 Switching to Binary mode.
Command:    PASV
Response:   227 Entering Passive Mode (162,243,89,203,209,5)
Command:    LIST
Error:  Connection timed out
Error:  Failed to retrieve directory listing

here is my firewall settings netstat -nL:

Chain INPUT (policy DROP)
target     prot opt source               destination         
ACCEPT     all  --  0.0.0.0/0            0.0.0.0/0           state RELATED,ESTABLISHED 
ACCEPT     tcp  --  0.0.0.0/0            0.0.0.0/0           tcp dpt:80 
ACCEPT     tcp  --  0.0.0.0/0            0.0.0.0/0           tcp dpt:443 
ACCEPT     tcp  --  0.0.0.0/0            0.0.0.0/0           tcp dpt:25 
ACCEPT     tcp  --  0.0.0.0/0            0.0.0.0/0           tcp dpt:587 
ACCEPT     tcp  --  0.0.0.0/0            0.0.0.0/0           tcp dpt:110 
ACCEPT     tcp  --  0.0.0.0/0            0.0.0.0/0           tcp dpt:995 
ACCEPT     tcp  --  0.0.0.0/0            0.0.0.0/0           tcp dpt:143 
ACCEPT     tcp  --  0.0.0.0/0            0.0.0.0/0           tcp dpt:993 
ACCEPT     tcp  --  0.0.0.0/0            0.0.0.0/0           tcp dpt:4785 
ACCEPT     icmp --  0.0.0.0/0            0.0.0.0/0           icmp type 8 
ACCEPT     all  --  0.0.0.0/0            0.0.0.0/0           
ACCEPT     tcp  --  0.0.0.0/0            0.0.0.0/0           tcp dpt:21 
ACCEPT     tcp  --  0.0.0.0/0            0.0.0.0/0           tcp dpt:20 
DROP       tcp  --  0.0.0.0/0            0.0.0.0/0           tcp flags:0x3F/0x00 
DROP       tcp  --  0.0.0.0/0            0.0.0.0/0           tcp flags:!0x17/0x02 state NEW 
DROP       tcp  --  0.0.0.0/0            0.0.0.0/0           tcp flags:0x3F/0x3F 

Chain FORWARD (policy DROP)
target     prot opt source               destination         

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination

here is my vsftpd.conf:

# Example config file /etc/vsftpd/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.
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.
#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
#
# The target log file can be vsftpd_log_file or xferlog_file.
# This depends on setting xferlog_std_format parameter
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
#
# The name of log file when xferlog_enable=YES and xferlog_std_format=YES
# WARNING - changing this filename affects /etc/logrotate.d/vsftpd.log
#xferlog_file=/var/log/xferlog
#
# Switches between logging into vsftpd_log_file and xferlog_file files.
# NO writes to vsftpd_log_file, YES to xferlog_file
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 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 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_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. To listen on IPv4 and IPv6
# sockets, you must run two copies of vsftpd with two configuration files.
# Make sure, that one of the listen options is commented !!
#listen_ipv6=YES

pam_service_name=vsftpd
userlist_enable=YES
tcp_wrappers=YES

Thanks in Advance!

Best Answer

FTP as protocol is a bit of an odd duck. It uses two TCP connections, rather than just the one most protocols use. You have TCP port 21, the command and login connection, and a second (random) TCP port, for the data connection.

With passive FTP the second connection is to a randomly assigned available TCP port above 1024.

You problems seem to indicate you don't have that second port open in your firewall.

There's multiple ways to deal with that:

Fix the PASV port(-range) One solution is to configure VSFTPD to use a small range of ports, or just a single port and create a firewall rule to open those ports:

# /etc/vsftpd/vsftpd.conf
# reserve TCP ports 2121-2142 for passive FTP
pasv_min_port=2121
pasv_max_port=2142

And then open the fixed port range in your firewall.

In an Linux iptables firewall the multiport module allows for a port range rather than 20 lines each opening a single port:

iptables -I INPUT -p tcp -m state --state NEW -m tcp -m multiport --dports 2121:2142 -j ACCEPT

The advantage of that method is that it also works with more complex setups of multiple firewalls, port forwarding, etc.

Use an intelligent firewall

With an inetlligent firewall you don't have to open up additional ports.
Since FTP is clear text protocol your firewall can scan the traffic on the command connection on port 21. It will recognise the PASV port that will be assigned and open up the firewall dynamically.

For Linux netfilter (iptables) firewalls there's a kernel module to do that for you: nf_conntrack_ftp also known as ip_conntrack_ftp . Load that module and you problems should be gone:

modprobe -i ip_conntrack_ftp

If you have a stateful firewall accepting RELATED traffic will then automatically allow the connection to the data port.

If that solves your FTP connection problems configure the module to be loaded at boot time. The RHEL6 and CentOS 6 method of doing that in this case is by way of:

# /etc/sysconfig/iptables-config 
# Space separated list of nat helpers (e.g. 'ip_nat_ftp ip_nat_irc'), which
# are loaded after the firewall rules are applied. Options for the helpers are
# stored in /etc/modprobe.conf.
IPTABLES_MODULES="nf_conntrack_ftp"
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