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iptables as "proxy" and a filter
Post 302927078 by Smiling Dragon on Sunday 30th of November 2014 07:02:17 PM
11-30-2014
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 
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
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.
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
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 DEBIAN
proxychains
proxychains(1) proxychains(1) NAME
ProxyChains - redirect connections through proxy servers SYNTAX
proxychains <program> DESCRIPTION
This program forces any tcp connection made by any given tcp client to follow through proxy (or proxy chain). It is a kind of proxifier. It acts like sockscap / premeo / eborder driver (intercepts TCP calls). This version (2.0) supports SOCKS4, SOCKS5 and HTTP CONNECT proxy servers. Auth-types: socks - "user/pass" , http - "basic". When to use it ? 1) When the only way to get "outside" from your LAN is through proxy server. 2) When you are behind restrictive firewall which filters outgoing connections to some ports. 3) When you want to use two (or more) proxies in chain: like: your_host <--> proxy1 <--> proxy2 <--> target_host 4) When you want to "proxify" some programs with no proxy support built-in (like telnet). 5) When you dont want to pay for eBorder / premeo socks driver :) Some cool features: * This program can mix different proxy types in the same chain like: your_host <-->socks5 <--> http <--> socks4 <--> http <--> target_host * Different chaining options supported like: take random proxy from the list. or : chain proxies in exact order or : chain proxies in dynamic order (smart exclude dead proxies from chain) *You can use it with any TCP client application, even network scanners. yes, yes - you can make portscan via proxy (or chained proxies) for example with Nmap scanner by fyodor (www.insecure.org/nmap). proxychains nmap -sT -PO -p 80 -iR (find some webservers through proxy) NOTE: to run suid/sgid programs(like ssh) through proxychains you have to be root FILES
proxychains looks for config file in following order: ./proxychains.conf $(HOME)/.proxychains/proxychains.conf /etc/proxychains.conf see more in /etc/proxychains.conf EXAMPLES
To run this program the standard way type: proxychains telnet targethost.com in this example it will run telnet through proxy(or chained proxies) specified by proxychains.conf COPYING
proxychains is distributed under the GNU General Public License. (GPL 2.0 or greater). AUTHORS
Net Creature, Proxy Labs <http://proxychains.sourceforge.net> <Net Creature> 2.0 proxychains(1)