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Old 07-11-2005, 05:45 PM   #1
Registered: Jun 2003
Location: SoCal
Distribution: CentOS
Posts: 465

Rep: Reputation: 30
open squid proxy

My ISP emailed me saying that people are accessing an open proxy on my network and are using it to send mass spam. How do I lock down my squid proxy so that internet users can not use my proxy server? I am using suse 9.3 to run my squid proxy. I'm not sure if suse handles its security different than iptables (SuSEFilewall2?).

My proxy server is sitting behind a hardware router with nat and all of the logs on my router look fine. Very few incoming and outgoing connections. Bascially its setup like:

DSL -> Router -> Squid Proxy/Gateway -> LAN

Any incoming connections to my proxy should be picked up by my routers logs right? Is it possible my ISP is making a mistake?

Last edited by msound; 07-11-2005 at 06:23 PM.
Old 07-11-2005, 06:50 PM   #2
Senior Member
Registered: Feb 2003
Location: The Real Washington
Distribution: Debian, Android
Posts: 1,819

Rep: Reputation: 46
First and most importantly, get it off the Internet until you get it fixed. Second, look in your squid.conf for the following entry

# TAG: http_port
# Usage: port
# hostnameort
# The socket addresses where Squid will listen for HTTP client
# requests. You may specify multiple socket addresses.
# There are three forms: port alone, hostname with port, and
# IP address with port. If you specify a hostname or IP
# address, then Squid binds the socket to that specific
# address. This replaces the old 'tcp_incoming_address'
# option. Most likely, you do not need to bind to a specific
# address, so you can use the port number alone.
# The default port number is 3128.
# If you are running Squid in accelerator mode, then you
# probably want to listen on port 80 also, or instead.
# The -a command line option will override the *first* port
# number listed here. That option will NOT override an IP
# address, however.
# You may specify multiple socket addresses on multiple lines.
# If you run Squid on a dual-homed machine with an internal
# and an external interface then we recommend you to specify the
# internal addressort in http_port. This way Squid will only be
# visible on the internal address.
# http_port 3128

Change the 3128 above to <yourinternalip>:3128

Squid by default listens to all interfaces. This is horrible for security. Set it to listen only on your internal ip, so that requests cannot originate from the web. Install sarg or squint to get a good look at who is using your squid proxy and for what.

Second, check your firewall. Go here for starters and run ShieldsUp

Do a scan for common ports and see if your port 3128 is open. If so, your firewall needs serious work..

Also, if they are using you to send spam, it is likely not squid that is the problem. You may have a mail server like Postfix, Exim, or Sendmail listening on your external interface as well. If you are not trying to run a mail server, for gods sake, shut them off.. You ISP is being nice, I have seen several people have their connections cut off with very little notice because of this. If you don't have a mail server running, look to your windows boxes. They may have trojan spam servers installed.

Last edited by Pcghost; 07-11-2005 at 06:55 PM.
Old 07-11-2005, 07:12 PM   #3
Registered: Jun 2003
Location: SoCal
Distribution: CentOS
Posts: 465

Original Poster
Rep: Reputation: 30
false alarm!

I called my ISP and they said that the incident happened on Friday at 12:36PM. That was the time we were servicing a laptop that had been infected with some kind of virus that was launching a DoS attack on another server. We immediately disconnected the laptop's network connection and removed the virus so it was a very isolated incident.

Everythings fine now thought and my ISP assured me that our broadband service would not be suspended ::sigh of relief::

Last edited by msound; 07-11-2005 at 07:23 PM.


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