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DNS Security Policy

• Introduction

• Common Requirements

• Intranet DNS Configuration Requirements

• Internet DNS Configurations Requirements

• Webliography

Introduction

If  DNS data is compromised, attackers can gain information about corporate network that can be used to compromise other services. For example, attackers can harm corporate in the following ways:

• By using zone transfer, attackers can retrieve a list of all the hosts and their IP addresses in corporate network.
• By using denial-of-service attacks on DNS, attackers can prevent e-mail from being delivered to and from your network, disable most commerce applications, redirect all Web server queries to non-existent server, etc.
• If attackers can change your zone data, they can set up fake Web servers, or cause all SMTP e-mail to be redirected to their servers.

The risk of an attack against a DNS server varies depending on the level of exposure to the Internet. For a DNS server in a private network that uses a private namespace, a private addressing scheme, and an effective firewall, the risk of attack is lower and the possibility of discovering the intruder is greater. For a DNS server that is exposed to the Internet, the risk is higher.

That means that required DNS security should be different between Intranet and Internet, althouth they should have a common core.

Common Requirements

1. Solaris should be used as an OS.  Only versions of Solaris 9 release 09/04 (final release of Solaris 9) or Solaris 10 releases 01/06 or higher are allowed

2. Bind 9.3 or higher are the only versions allowed. Bind 8 should be eliminated by 2006.

3. Bind should be complied using Sun Studio 11 compiler.

4. Each authoritative DNS server (master and slaves) should be implemented on a standalone Solaris server that runs only bind.

5. Sharing DNS with other services on a server is explicitly prohibited (with the exception of strong authentication clients). For example, running Web server or other externally accessible diamonds are prohibited. DNS servers should not act as NTP servers unless Solaris 10 is used and each services uses a separate zone.

6. Bind should be installed in chrooted environment or by creating an RBAC role (for example dnsuser).

7. Bind should run as a non-root user

8. Internal Firewall should be installed on the server.  IP filter is acceptable.

9. Only ssh access should be allowed to the server. No telnet or ftp assess should be allowed.

10. Only Secure ID authenticated users are allowed on the server.  No application or user accounts without strong authentication are allowed. That explicitly includes all  non-SNMP monitoring tools that use telnet or other insecure protocols.

11. SNMP requests should be controlled by firewall.

12. Solaris should be hardened as a bastion firewall. Stack protection should be enabled.

13. The DNS servers should have their clocks synchronized via NTP.  For this purpose, servers and their internal firewalls should allow the DNS servers to be NTP clients. 

14. All attempts at intrusion or other compromise should be  logged, and all such logs from all DNS servers should be send to central LOGHOST.  DNS Servers should log in GMT to facilitate log comparison.

15. Each DNS server should keep statistics on the amount and types of queries received/answered on a daily basis. These          statistics must be made available to security team on daily basys by email or other suitable protocols.            
     

Intranet DNS Configuration Requirements

Corporate  intranet should be configured as private DNS address space (intranet space). Intranet DNS servers security policy includes the following characteristics:

1. DNS servers permit zone transfers to only servers and workstations with static IP. 
2. DNS servers use static IP addresses in 10 network.
3. All Internet name resolution is performed by using proxy servers and gateways.
4. Secondary DNS servers should be installed only on segments that are accessible via at least  two different routers (no "single chokepoint segments")

Internet DNS Configurations Requirements

Security policy includes the following characteristics:

1. Recursion should be disabled on all DNS servers.
2. All DNS servers should limit zone transfers to explicitly specified set of IP addresses. 

Webliography

***** [PDF] Securing an Internet Name Server CERT paper based on Cricket Liu presentation

Domain name system (DNS) servers translate names suitable for use by people (such as www.example.com) into network addresses (e.g., 192.168.4.22) suitable for use by computers. There are a number of different name server software packages available today. Berkeley Internet Name Domain (BIND), produced by the Internet Software Consortium (http://www.isc.org), is the most widely deployed name server package, and is available on a wide variety of platforms. Other popular DNS packages include Microsoft DNS and djbdns. The goal of this document is to discuss general name server security. However, in order to provide useful examples we have chosen to focus on BIND since it is the most commonly used software for DNS servers. Risks to name servers Name servers exposed to the Internet are subject to a wide variety of attacks:

• Attacks against the name server software may allow an intruder to compromise the server and take control of the host. This often leads to further compromise of the network.
• Denial of service attacks, even one directed at a single DNS server, may affect an entire network by preventing users from translating hostnames into the necessary IP addresses.
• Spoofing attacks that try to induce your name server to cache false resource records, and could lead unsuspecting users to unsavory sites.
• Information leakage from a seemingly innocent zone transfer could expose internal network topology information that can be used to plan further attacks.

 A name server could even be an unwitting participant in attacks on other sites. While it is important for network administrators to secure any host connected to the Internet, they must give name servers special consideration due to the important role they play. The purpose of this document is to outline some common steps that can be taken to secure an Internet Name Server from various types of attacks. Run a new version of your name server software As with any piece of software, name server software evolves with each release. Virtually all older name servers have widely known vulnerabilities that can be exploited. Vulnerabilities that appear in one version are usually fixed in subsequent releases. While running the newest version of your name server software doesn’t guarantee your server’s security, it minimizes the possibility of exploitation. When upgrading, be sure to read the release notes to understand what has been fixed and what has been changed in the software. Upgrading the name server to a new version may require that changes be made to the configuration in order to provide the expected performance or to take advantage of new features.

Secure BIND Template By Rob Thomas

Chroot-BIND HOWTO By Scott Wunsch

August 11, 2005: Draft NIST Special Publication 800-81, Secure Domain Name System (DNS) Deployment Guide

Adobe .pdf file (654 KB)

NIST SP 800-81, Secure Domain Name System (DNS) Deployment Guide, is now available for public comments. The document provides deployment guidelines for securing the Domain Name System (DNS) in an enterprise. The security objectives for each DNS component are developed through analysis of threats and secure deployment guidelines are provided through combination of configuration options and checklists. The deployment guidelines cover Internet Engineering Task Force's (IETF) Request for Comments (RFCs) 4033, 4034, 4035 and 3833 (collectively called the DNSSEC specifications) as well as RFCs 2845 and 3007 (collectively called the TSIG specifications). Comments should be submitted to 800-81comments@nist.gov with "Comments on Public Draft SP 800-81" in the subject line. The comment period closes at 5:00 EST (US and Canada) on September 29th, 2005. Comment period is now CLOSED.

rfc4033

The Domain Name System Security Extensions (DNSSEC) add data origin  authentication and data integrity to the Domain Name System.  This    document introduces these extensions and describes their capabilities and limitations.  This document also discusses the services that the    DNS security extensions do and do not provide.  Last, this document    describes the interrelationships between the documents that collectively describe DNSSEC.