Security Basics mailing list archives
RE: how to block connections running on non-default ports
From: "AMOL" <amol.sable () capsilon com>
Date: Mon, 22 Aug 2005 14:53:26 +0530
Hi Niranjan, Nice question! Any IDS in inline mode, or Firewall will block the packets as per the rules defined for blocking/allowing. Generally,Port 80-HTTP and 443-HTTPS are among the most common ports in the "allowed" ones. And yes; your Firewall doesn't know more than source (IP:PORT) destination (IP:PORT) and state (if you have an option of a stateful inspection of packets).
From your scenario it looks like you have a packet filter Firewall.A
firewall implemented with the Packet Filters work at Network Layer of ISO/OSI stack. Hence it cant stop telnet connection to the server listening on "allowed" port. Similar is the case for Inline IDS. But as a security measure you can make sure that hosts on your network are NOT practicing things like: running telnet server on port 443. Strictly. And you can implement ALG (or simply enable it if its already present)option in your Firewall. A firewall implemented with the Application Layer Gateways(ALG) work at the Application Layer of ISO/OSI stack. Hope this may help a little. Regards --Amol. -----Original Message----- From: Niranjan S Patil [mailto:niranjan.patil () gmail com] Sent: Monday, August 15, 2005 9:06 PM To: security-basics () securityfocus com Subject: how to block connections running on non-default ports Hi list, I recently noticed that our corporate IDS could not block some of connections that are seemingly unauthorised. I launched a telnet connection to a remote server on Internet on port 23 and it was successfully blocked by our firewall. I change the listening port of the telnet server to 443 and launched another telnet connection on port 443. Neither our firewall or IDS was able to block this connection. Aren't IDS supposed to block such masqueraded connections, i.e., protocols with non-default ports. I have less knowledge on IDS, but isn't it simple for them to check packet headers and block/filter if they are not on right protocol/port? Is this normal with all IDS? Any help is appreciated. -- Regards, Niranjan S Patil
Current thread:
- how to block connections running on non-default ports Niranjan S Patil (Aug 16)
- RE: how to block connections running on non-default ports Burton Strauss (Aug 22)
- RE: how to block connections running on non-default ports AMOL (Aug 22)
- RE: how to block connections running on non-default ports James Scott-Brown (Aug 22)
- <Possible follow-ups>
- RE: how to block connections running on non-default ports Smith, Ryan (Aug 22)
- RE: how to block connections running on non-default ports Roger A. Grimes (Aug 22)
- RE: how to block connections running on non-default ports abretten (Aug 23)
- Re: RE: how to block connections running on non-default ports nospam_securityfocuscom (Aug 23)