Security Basics mailing list archives
RE: Securing DNS Server
From: "Steven Schullo" <sschullo () attbi com>
Date: Wed, 6 Nov 2002 10:36:13 -0600
Naman, Unless this DMZ DNS system will provide name lookups for public clients, you only need to ensure your public to DMZ gateway/firewall/router will allow outbound syn connections and inbound ack connections to the DMZ DNS box. This will effectively limit any public system from establishing a connection to the DMZ DNS box and will allow outbound resolutions. You can further limit communications by enabling traffic on port 53 TCP/UDP and upper level ports (1024 and up). If this system will be providing name lookups for public clients, you will have to open up UDP/TCP 53 inbound as well. This will open you up to potential DNS attacks. Best practice dictates that the DMZ DNS box be completely separate from internal DNS. IF this is the case, the DNS table should be somewhat basic and easy to recreate. This box should have root hints on it or forwarders set up for non-authoritative name resolution. Hope this helps. Steven L. Schullo, CISSP, MCSE, CCNA (469) 855-3228 mailto:sschullo () attbi com -----Original Message----- From: Naman Latif [mailto:naman.latif () inamed com] Sent: Monday, November 04, 2002 2:59 PM To: Michael Vaughan; security-basics Subject: RE: Securing DNS Server You are right for most of your assumptions. We do have an internal DNS server, which is Primary for all the users. No user has access to the DMZ DNS Server. Also the Internal DNS server is NOT accessible from outside. However the internal DNS server has the DMZ DNS server as its forwarder. So if an internal user query cannot be resolved by the internal DNS server, it is forwarded to the DMZ DNS Server.This is where my questions is, 1. If the DMZ DNS server needs to contact some external (root)server for resolving the query, then how do I control that ? Regards \\ Naman
-----Original Message----- From: Michael Vaughan [mailto:list () predator-hunter com] Sent: Monday, November 04, 2002 12:50 PM To: Naman Latif; 'security-basics' Subject: RE: Securing DNS Server -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Folks, If I am not mistaken, the DNS server in the DMZ should be a SECONDARY IE: a non-writable database. Furthermore, the DNS server on your internal network should be the primary giving ONLY appropriate information regarding the location of external services. IE: not allowing DNS zone transfers except from specific servers...etc. Essentially, the external DMZ server services external requests for resolving services offered in the DMZ ONLY and the internal DNS server (Primary) offers services to internal clients for resolving outside sites & services. My question is why would you be allowing ANY outgoing connections from your DMZ DNS server to external root servers other than what is on your site? If you have other services located at other locations...you can add those to the DNS manually or through zone transfer. I would propose that the DMZ DNS server should ONLY resolve your DMZ services and no one else's. IE: Why would I want someone using my DNS server externally to resolve yahoo? Basically I am saying that if the service can not be resolved externally to your site(s) then it should fail. Your internal DNS server would service all of your internal clients and would not be accessible from external sources period. There are notable exceptions depending on your requirements but am I missing the point of your question? I am assuming you have a DMZ and you are in NO WAY allowing anyone to connect to your internal network directly. Is that correct? - -Michael Vaughan mvaughan () predator-hunter com http://www.predator-hunter.com The information contained in this message may contain privileged and confidential information and is intended only for the internal company use of the individual or entity named above. If the reader of this message is not the intended recipient, or the employee or agent responsible to deliver it to the intended recipient, you are hereby notified that any examination, distribution or copying of this communication is strictly prohibited. Furthermore, any and all recipients of this message are prohibited from engaging in the unauthorized dissemination of the information contained herein to person(s) outside the company. If you have received this communication in error, please notify sender immediately. - -----Original Message----- From: Naman Latif [mailto:naman.latif () inamed com] Sent: Friday, November 01, 2002 7:31 PM To: security-basics Subject: Securing DNS Server Hi, I am trying to restrict Access to our DNS Server from Outside using a Cisco IOS Firewall. Initially we only had Port 53 Access to this Server from outside. But it turned out that when our DNS Server has to query a root name server, it sends out a UDP query with a random higher (>1023) source port number, which means that I will have to open >1023 Ports access to this server from outside. In this situtation How do I protect my DNS server from outside attacks on higher port numbers ? Is there a range of Source Port numbers that a BIND DNS server would use, when querying outside servers ? -----BEGIN PGP SIGNATURE----- Version: PGP 7.0.4 iQA/AwUBPcbdZuqV6OTyHFF7EQJoPgCgxyxV0964WY3BFQAuj6VxxzXpZ3QAoKNc zjic3/Q9TAzAe8FYYqGSt66i =oLS0 -----END PGP SIGNATURE-----
Current thread:
- Securing DNS Server Naman Latif (Nov 04)
- RE: Securing DNS Server Michael Vaughan (Nov 05)
- RE: Securing DNS Server Daniel Miessler (Nov 05)
- Re: Securing DNS Server Bennett Todd (Nov 08)
- <Possible follow-ups>
- RE: Securing DNS Server Naman Latif (Nov 05)
- RE: Securing DNS Server Steven Schullo (Nov 06)
- RE: Securing DNS Server Mustafa Baig (Nov 06)
- RE: Securing DNS Server Naman Latif (Nov 06)
- Re: Securing DNS Server Bennett Todd (Nov 06)