iptables as "proxy" and a filter Post: 302927078

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Special Forums IP Networking Proxy Server iptables as "proxy" and a filter Post 302927078 by Smiling Dragon on Sunday 30th of November 2014 07:02:17 PM

11-30-2014

Registered User

One thing I note in your friend's script is that it sets the firewall to drop all incoming connections before allowing port 22 (ssh) connections. If something goes wrong along the way on this, you'll need console access to get back in :/ I'd recommend setting the -P INPUT DROP last tbh Smilie

As you've noted, this is just INPUT filters, your one is just NAT/IPMASQ. So it's like comparing apples and oranges really.

Looking just at your rules, I don't see anything untoward there, it appears that you are causing the proxy to accept traffic arriving on port 80 and redirecting it to 5.196.130.245.

An external customer connecting to the address would not be able to detect the redirect and would see all their connections as going to and coming back from the address of your proxy.
The webserver would see all the connections as coming from the proxy server address, unless the customer is setting "X-Forwarded-For" headers in their requests (not all that uncommon to find) which would be passed along to the webserver and quite possibly included in it's logs.

If you have a little more background of what your end goal is, we might be able to offer more advice Smilie

I would recommend also adding a FORWARD rule to DROP anything not for that port arriving from the external interface, as you've turned on IP forwarding and at present your setup would happily forward anything anyone asks it to. It's note really serious but could exacerbate any existing security issue into a full exploit.

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LEARN ABOUT FREEBSD

tftp-proxy

TFTP-PROXY(8)						    BSD System Manager's Manual 					     TFTP-PROXY(8)

NAME

     tftp-proxy -- Internet Trivial File Transfer Protocol proxy

SYNOPSIS

     tftp-proxy [-v] [-w transwait]

DESCRIPTION

     tftp-proxy is a proxy for the Internet Trivial File Transfer Protocol invoked by the inetd(8) internet server.  TFTP connections should be
     redirected to the proxy using the pf(4) rdr command, after which the proxy connects to the server on behalf of the client.

     The proxy establishes a pf(4) rdr rule using the anchor facility to rewrite packets between the client and the server.  Once the rule is
     established, tftp-proxy forwards the initial request from the client to the server to begin the transfer.	After transwait seconds, the pf(4)
     NAT state is assumed to have been established and the rdr rule is deleted and the program exits.  Once the transfer between the client and
     the server is completed, the NAT state will naturally expire.

     Assuming the TFTP command request is from $client to $server, the proxy connected to the server using the $proxy source address, and $port is
     negotiated, tftp-proxy adds the following rule to the anchor:

	   rdr proto udp from $server to $proxy port $port -> $client

     The options are as follows:

     -v      Log the connection and request information to syslogd(8).

     -w transwait
	     Number of seconds to wait for the data transmission to begin before removing the pf(4) rdr rule.  The default is 2 seconds.

CONFIGURATION

     To make use of the proxy, pf.conf(5) needs the following rules.  The anchors are mandatory.  Adjust the rules as needed for your configura-
     tion.

     In the NAT section:

	   nat on $ext_if from $int_if -> ($ext_if:0)

	   no nat on $ext_if to port tftp

	   rdr-anchor "tftp-proxy/*"
	   rdr on $int_if proto udp from $lan to any port tftp -> 
	       127.0.0.1 port 6969

     In the filter section, an anchor must be added to hold the pass rules:

	   anchor "tftp-proxy/*"

     inetd(8) must be configured to spawn the proxy on the port that packets are being forwarded to by pf(4).  An example inetd.conf(5) entry fol-
     lows:

	   127.0.0.1:6969  dgram   udp	   wait    root 
		   /usr/libexec/tftp-proxy tftp-proxy

SEE ALSO

     tftp(1), pf(4), pf.conf(5), ftp-proxy(8), inetd(8), syslogd(8), tftpd(8)

CAVEATS

     tftp-proxy chroots to /var/empty and changes to user ``proxy'' to drop privileges.

BSD
								 November 28, 2005							       BSD