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#1 2016-07-25 05:41:01

coffeedemugger
Member
Registered: 2016-07-25
Posts: 1

vsftpd and iptables

This must be very simple, but I've been stuck on this problem for the last six hours.

I have vsftpd working.  I can connect on localhost.  I can connect remotely with my iptables disabled.  When my iptables are on, though, my remote connection is rejected.   Almost proper function, but not exactly what I'm going for here.  I changed the vsftpd port from 21 to 8888 and my iptables (Hopefully) reflects that.  I also host an ssh server on 88889.  Here are those:

/etc/iptables/iptables.conf:

*filter
:INPUT DROP [0:0]
:FORWARD DROP [0:0]
:OUTPUT ACCEPT [51:8296]
:LOG_AND_DROP - [0:0]
:TCP - [0:0]
:UDP - [0:0]
-A INPUT -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
-A INPUT -i lo -j ACCEPT
-A INPUT -m conntrack --ctstate INVALID -j DROP
-A INPUT -p icmp -m icmp --icmp-type 8 -m conntrack --ctstate NEW -j ACCEPT
-A INPUT -p udp -m conntrack --ctstate NEW -j UDP
-A INPUT -p tcp -m tcp --tcp-flags FIN,SYN,RST,ACK SYN -m conntrack --ctstate NEW -j TCP
-A INPUT -p udp -j REJECT --reject-with icmp-port-unreachable
-A INPUT -p tcp -j REJECT --reject-with tcp-reset
-A INPUT -j REJECT --reject-with icmp-proto-unreachable
-A INPUT -p tcp -m tcp --dport 88889 -m state --state NEW -m recent --set --name DEFAULT --mask 255.255.255.255 --rsource
-A INPUT -p tcp -m tcp --dport 88889 -m state --state NEW -m recent --update --seconds 90 --hitcount 4 --name DEFAULT --mask 255.255.255.255 --rsource -j LOG_AND_DROP
-A INPUT -p tcp -m tcp --dport 88889 -j ACCEPT
-A INPUT -p tcp -m state --state NEW -m tcp --dport 8888 -j ACCEPT
-A LOG_AND_DROP -j LOG --log-prefix "iptables deny: " --log-level 7
-A LOG_AND_DROP -j DROP
-A TCP -p tcp -m tcp --dport 88889 -j ACCEPT
COMMIT
# Completed on Sun Jul 24 13:11:55 2016

/etc/vsftpd.conf:

# 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.
#
# 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

userlist_deny=NO
userlist_file=/etc/vsftpd.user_list
#
# 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
#
# 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.
# 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=Paul's 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().
# (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
listen_port=8888

pasv_min_port=49152
pasv_max_port=65534

seccomp_sandbox=NO

#
# 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

/etc/modprobe.d/ip_conntrack_ftp.conf:

options nf_conntrack_ftp ports=8888

/etc/modules-load.d/nf_conntrack_ftp.conf:

nf_conntrack_ftp

Now please bear with me, I don't know anything about modprobe or iptables, really, so if anything strikes you as odd, please let me know.

Last edited by coffeedemugger (2016-07-25 05:43:59)

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#2 2016-07-26 14:01:22

paulkerry
Member
From: Sheffield, UK
Registered: 2014-10-02
Posts: 611

Re: vsftpd and iptables

coffeedemugger wrote:

pasv_min_port=49152
pasv_max_port=65534

Unless I have missed something: the above lines in your config file specify the above incoming port ranges, but I cannot see that range being allowed through your iptables.
Perhaps add something like...

-A INPUT -p tcp --destination-port 49152:65534 -j ACCEPT

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#3 2016-07-26 18:15:49

brebs
Member
Registered: 2007-04-03
Posts: 3,742

Re: vsftpd and iptables

See e.g. active and passive FTP.

Don't use "--tcp-flags" unless you're an expert. Normal rulesets won't need such leetness.

Use logndrop to do your own debugging, rather than just REJECTing and DROPing blindly.

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#4 2016-07-27 17:28:06

moose jaw
Member
From: Milwaukee
Registered: 2007-08-20
Posts: 104

Re: vsftpd and iptables

You've got this:

-A INPUT -p tcp -j REJECT --reject-with tcp-reset

before this:

-A INPUT -p tcp -m state --state NEW -m tcp --dport 8888 -j ACCEPT

I am not an iptables expert, but I believe that your 8888-bound packets are never hitting that second rule because they're being rejected by the first one. In other words, you have a rule ordering problem.

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