RE: WuFTP server with Iptables.

From: Mark Johnston (mark.johnston_at_bluesq.com)
Date: 09/28/04

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    Date: Tue, 28 Sep 2004 10:37:53 +0100
    To: "Jari IT" <jari_info@yahoo.uk.co>, <security-basics@securityfocus.com>
    
    

    Hey there,

    You might want to look at using the stateful mode of the firewall ... so it would look something like this ... you can add interfaces and destination IP's if you like.

    iptables -A INPUT -p tcp --dport 21 -m state --state NEW,ESTABLISHED -j ACCEPT
    iptables -A OUTPUT -p tcp --sport 21 -m state --state ESTABLISHED -j ACCEPT

    You can then use the "RELATED" state to allow traffic for port 20 instead of creating new rules to specfically allow this.

    Cheers
    Mark

    -----Original Message-----
    From: Jari IT [mailto:jari_info@yahoo.uk.co]
    Sent: 25 September 2004 05:55
    To: security-basics@securityfocus.com
    Subject: WuFTP server with Iptables.

    Hi all,

    I am setting a FTP server with Iptable firewall.
    Here is the rule, which I get from www.openna.com.

        # incoming request
        iptables -A INPUT -i $EXTERNAL_INTERFACE -p tcp \
                 --source-port $UNPRIVPORTS \
                 -d $IPADDR --destination-port 21 -j ACCEPT

        iptables -A OUTPUT -o $EXTERNAL_INTERFACE -p tcp ! --syn \
                 -s $IPADDR --source-port 21 \
                 --destination-port $UNPRIVPORTS -j ACCEPT

        # PORT MODE data channel responses
        iptables -A OUTPUT -o $EXTERNAL_INTERFACE -p tcp \
                 -s $IPADDR --source-port 20 \
                 --destination-port $UNPRIVPORTS -j ACCEPT

        iptables -A INPUT -i $EXTERNAL_INTERFACE -p tcp ! --syn \
                 --source-port $UNPRIVPORTS \
                 -d $IPADDR --destination-port 20 -j ACCEPT

        # PASSIVE MODE data channel responses
        iptables -A INPUT -i $EXTERNAL_INTERFACE -p tcp \
                 --source-port $UNPRIVPORTS \
                 -d $IPADDR --destination-port $UNPRIVPORTS -j ACCEPT

        iptables -A OUTPUT -o $EXTERNAL_INTERFACE -p tcp ! --syn \
                 -s $IPADDR --source-port $UNPRIVPORTS \
                 --destination-port $UNPRIVPORTS -j ACCEPT

    However, I still cannot connect from my house (behind ADSL router/modem) to
    that site.
    Stop this firewall, the FTP server work well.

    Please advice me about this.
    Thanks in advance,
    Jari

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