Hardening the BIND v8 DNS Server

boran.com/security/sp/bind_hardening8.html

boran.com/dns
Sean Boran

March 07, 2001 - This paper presents the risks posed by an insecure DNS server and walks through compiling, installing, configuring and optionally, chroot'ing BIND 8. The test environment is Solaris 2.5, 2.6, 7 and 8. Many configuration and troubleshooting tips are provided, along with up-to-date references on BIND and alternatives for NT, Linux and Solaris.

Italian readers: please note that this article has also been translated into Italian [9].

Update: Mar. 30, 2001

NOTE that Bind9 is discussed in another paper bind9_20010430.html.

  1. Introduction: Why bother? What risks does an insecure BIND pose?
  2. Install and Configure BIND: compile, install, create DNS data, start BIND.
  3. Chroot'ing BIND: Create chroot jail, copy BIND to jail, start BIND.
  4. Troubleshooting
  5. Configuration Notes
  6. Footnotes
  7. References


Introduction

Your Domain Name Service is the road sign to your systems on the Internet. No matter how secure and robust your Web, mail and other servers are, compromised and corrupted DNS systems can prevent customers and legitimate users from ever reaching you. DNS, like many of the older protocols, was developed at a time when the Internet was a kinder, gentler place and was meant to provide a simple and unlimited way to provide information about what computers you have to anyone else. Obviously, the model of the Internet has changed, and changes to BIND (Berkeley Internet Name Domain software, the most common implementation of DNS), along with widely accepted configuration guidelines, have improved our ability to lock down DNS.

BIND [1] is the most frequently used DNS server and maintained by the ISC. It is also known as "named", since this is the name of the actual daemon itself. BIND has a long history, is a core tool for most Internet sites. As with many applications exposed to the increasingly hostile Internet environment, security weaknesses have been discovered in BIND. There are three  major versions:

  1. v4 was bundled with most UNIX systems up to around 1998. It has been abandoned by most vendors, except, interestingly, OpenBSD. The OpenBSD crew audited and corrected v4 and found v8 to be overly complex, thus preferring to stick with what they trust, even if v4 doesn't have all the bells and whistles of v8/v9.
  2. v8 is the current versions used by most sites. This article provides a step-by-step guide for version 8 (e.g. 8.2.3).
  3. v9 is a major new version: a complete re-write, free, but commercially sponsored. It has lots of new features (which is nice, but a security concern). v9 reached production status in October 2000 and the current stable version is v9.1.1.

    The ISC recommends that BIND v9 be used, which is a complete rewrite of the BIND server. Personally, I've been reluctant to go to v9, since it's a complete rewrite and one would expect quite a few bugs in such a scenario. It is now several months old, however, and did not suffer from the new weaknesses published in of January 2001 (which is a good sign).

    In March/April of 2001 I took the plunge and setup several v9 servers. It worked out quite well and a new article has been published separately [10]. I'll be focussing updates on the new v9 article in the future.


Why Bother? What Risks Does an Insecure BIND Pose?

So what, you say? Yet another program with security problems? There are so many problems in so many applications these days, it's just not possible to keep up with all these advisories and patches. Do we really have to worry about DNS too? Well, a compromised DNS server can pose some interesting risks:

  1. An attacker can gain much interesting information if zone tranfers are allowed: the entire list of hosts and routers with IP addresses, names and possible even comments indicating location, names etc.
  2. Denial of service: If all your Internet DNS servers go down,
  3. Loss of integrity: If an attacker can change the DNS data or spoof other sites into believing false data (this is known as DNS poisoning), it gets very dangerous:


So What Needs to Be Done?

BIND weakness may be addressed with several prevention measures, but detection and reaction shouldn't be forgotten either:

  1. Resource isolation: Use a dedicated, hardened server for Internet DNS, don't share with other services, and especially do not allow user logins. Minimal services/users means reducing the amount of software running and hence the amount exposed to network attacks. Separation prevents other services or users possibly using local weakness in the system to attack BIND.
  2. Redundancy: Install a secondary on a different Internet connection (foreign branch of your company, another ISP, etc.). If your site dies, at least other sites won't think you "cease to exist"; they just think you're "not available," so tPhat emails, for example, won't get lost be will be queued (typically up to four days).
  3. Use the latest version (i.e. 8.2.3 or 9.1 or later).
  4. Access control: Restrict zone transfers to minimize the amount of information on your networks available to attackers. Consider using transaction signatures. Consider restricting/not allowing recursive queries.
  5. Run BIND with minimum privileges: as a non-root user, with a tight umask.
  6. More resource isolation: Run BIND in a "chroot" jail, so it is much more difficult for a compromised bind daemon to damage the operating system or compromise other services.
  7. Configure BIND not to report it's version number (see below). Some people don't believe in hiding the version number, as it is "security by obscurity," but I maintain that it at least helps against the script kiddies who are roaming the net looking for obvious targets. Defending against the pros is a different matter.
  8. Detection: Monitor logs for unusual activity and the system for unauthorized changes with an integrity checker.
  9. Keep an eye on relevant advisories, make sure your are notified of future BIND problems in a timely manner.

The procedure in this paper concentrates only on measures 4), 5) and 6), which should help to protect a server against possible future weakness in BIND. This procedure has been tested on several production systems: a secondary on Solaris 2.5 + 2.8, a primary on Solaris 2.6 + 2.7.


Install and Configure BIND

It is assumed that Solaris is up and running and appropriately hardened and that the BIND delivered with Solaris is disabled. If you have not yet hardened Solaris, check out the YASSP tool first [7]. This section runs through:

  1. Compiling BIND on a master host, since you probably don't have (or shouldn't have) a compiler on the hardened DNS server.
  2. Copying and installing BIND on the DNS server.
  3. Setting up DNS data files.
  4. Running BIND.


1. Compiling BIND (on a host with a compiler).

Download the distribution [1], and extract it to a subdirectory and compile. This can be done as any user.
Note: It is recommended that "GNU make" be installed first, so that the installation to a temporary directory below works correctly.

cd src;
make clean;
make depend && make;

Now change to the root account, install to a temporary directory, and create a tarball:

su - root
# allow group, but not world access
umask 027
make install DESTDIR=/tmp
cd /tmp/usr/local
tar cf - * | compress > bind_dist.tar.Z


2. Copy and install BIND on the DNS server

Create a user and group account for BIND:

echo "named:x:20000:20000:BIND DNS daemon:/tmp:/bin/false" >> /etc/passwd
echo "named:NP:6445::::::"  >> /etc/shadow
echo "named::20000:" >> /etc/group

Don't allow the BIND account to use ftp:

echo "named" >> /etc/ftpusers

Copy bind_dist.tar.Z to /usr/local on the DNS server and extract into /usr/local:

zcat bind_dist.tar.Z | tar xvf -

Set up file permissions:

cd /var; mkdir named
chown -R root:named named
chmod 770 named

touch /var/run/named.pid;
chown named:named /var/run/named.pid;

chmod 755 /usr/local /usr/local/bin /usr/local/sbin /usr/local/etc

chown root:named /usr/local/bin/{dig,dnsquery,nslookup,nsupdate,host};

chmod 755 /usr/local/bin/ /usr/local/bin/{dig,dnsquery,nslookup,nsupdate,host};

chown root:named /usr/local/sbin/{dnskeygen,irpd,named,named-bootconf,named-xfer,ndc};

chmod 755 /usr/local/sbin/{dnskeygen, irpd,named,named-bootconf,named-xfer,ndc};

Optionally, you can rename the default DNS binaries installed on the system, so that they are not used by accident, and leave a reminder.

cd /usr/sbin;
mv nslookup nslookup.old
mv nsupdate nsupdate.old
mv in.named in.named.old
mv named-bootconf named-bootconf.old
mv named-xfer named-xfer.old
touch NAMED_NOW_IN_USR_SBIN

Add /usr/local/sbin to the root PATH in /.cshrc or /.profile.


3. Setting up DNS data files

cd /usr/local/etc
vi named.conf
chown root:named named.conf
chmod 640 named.conf

So what do you put in named.conf? Have a look at the examples provided in [2]. The file consists of options, logging, ACL, server and Zone sections. Some of the directives are:

After setting up named.conf, the files containing the DNS records have to be set up on primaries (in /var/named in our example); these are automatically downloaded by secondaries.


4. Running BIND

Check the console and syslog (daemonlog) for errors, e.g.

tail -f local0log | grep "named"

Start BIND:

/usr/local/sbin/named -u named

Configure automatic starting on boot
In /etc/init.d/inetsvc, change the DNS startup lines to:

# Start the BIND DNS server:
if [ -f /usr/local/sbin/named -a -f /usr/local/etc/named.conf ]; then
  echo "Starting BIND domain name server."
  /usr/local/sbin/named -u named;

Before moving on to the next stage, BIND should be working well, with no errors in the logs. See also the troubleshooting section.


Chroot'ing BIND

This process has three steps: create a general chroot jail, install BIND into the jail, start and test the chroot'ed BIND.

Set up a general chroot environment

BIND is now up and running, but we want to tighten security further by forcing it to run in a chroot environment (also called a jail or padded cell: Basically, restrict the files visible to BIND to a subdirectory within the file system). See also footnote [2] for a discussion of chroot environments.

We will now walk through the steps for setting up the chroot environment, copying over the BIND files, starting BIND and troubleshooting. These steps chroot the entire BIND program, not just using BIND's "-t" feature (see Note 1).

The following steps assume use of the C-Shell. We start by setting a variable for the chroot environment (jail) location, and setting umask so that all files copied can be read by both groups and world. These commands are designed to be copied and pasted.

1. Set source and destination directories

csh
set jail='/home/dns';
umask 022;

2. Set up empty directories and links:

mkdir $jail;
cd $jail;
mkdir -p {dev,opt,usr,var,etc};
mkdir -p var/{run,log,named} usr/{local,lib};
mkdir -p usr/share/lib/zoneinfo;

3. Setup /etc

cp /etc/{syslog.conf,netconfig,nsswitch.conf,resolv.conf,TIMEZONE} $jail/etc

4. Create a user and group account within chroot and for the whole system. BIND will run under this account.

echo "named:x:20000:20000:BIND DNS daemon:/tmp:/bin/false" >> /etc/passwd
echo "named:x:20000:20000:BIND DNS daemon:/tmp:/bin/false" > $jail/etc/passwd

echo "named:NP:6445::::::"  >> /etc/shadow
echo "named:NP:6445::::::"  > $jail/etc/shadow

echo "named::20000:" >> /etc/group
echo "named::20000:" > $jail/etc/group

5. Set up libraries:

Use ldd to see what shared object libraries named and named-xfer rely on:

ldd /usr/local/sbin/named /usr/local/sbin/named-xfer

Copy the files listed by ldd, for example for Solaris 2.6/7:

cp -p /usr/lib/libnsl.so.1 \
/usr/lib/libsocket.so.1 /usr/lib/libc.so.1 \
/usr/lib/libdl.so.1 /usr/lib/libmp.so.2 $jail/usr/lib

On Solaris 2.5:

cp -p /usr/lib/libnsl.so.1\
/usr/lib/libsocket.so.1 /usr/lib/libc.so.1\
/usr/lib/libdl.so.1 /usr/lib/libmp.so.1 /usr/lib/libw.so.1\
/usr/lib/libintl.so.1 $jail/usr/lib

Experience has shown the following are also needed for Solaris 2.5/6/7:

cp /usr/lib/ld.so.1 /usr/lib/nss_files.so.1 $jail/usr/lib

And with v8.2.3 on Solaris 8:

cp /usr/lib/libl.so.1 $jail/usr/lib

("Experience" means that first attempts didn't work, but by running BIND with truss, one could see what libraries were being sought after.)

6. Copy over Timezone files (I use MET, here in Europe):

mkdir -p $jail/usr/share/lib/zoneinfo;
cp -p /usr/share/lib/zoneinfo/MET $jail/usr/share/lib/zoneinfo/MET

7. Set up devices for communication, console, syslog, etc.

cd $jail/dev
mknod tcp c 11 42
mknod udp c 11 41
mknod log c 21 5
mknod null c 13 2
mknod zero c 13 12
chgrp sys null zero
chmod 666 null
mknod conslog c 21 0
mknod syscon c 0 0
chmod 620 syscon
chgrp tty syscon
chgrp sys conslog

Copying BIND to the Jail

We assume bind was already in /usr/local, so copy the BIND files over from there:

cd $jail;
mkdir -p usr/local/{bin,lib,sbin,bind,etc}
cd $jail/usr/local/sbin;
(cd /usr/local/sbin; tar cf - dnskeygen named* irpd ndc ) |tar xvf -
cd $jail/usr/local/bin;
(cd /usr/local/bin; tar cf - dnsquery dig host nslookup nsupdate) |tar xvf -
cd $jail/usr/local;
cp /usr/local/etc/named.conf etc;
(cd /usr/local; tar cf - bind) |tar xvf -

Your DNS data can be located in several directories; here we present two examples. The location is specified in named.conf.

1. Data in /etc/named

mkdir -p $jail/etc/named;  cd $jail/etc/named;
chgrp named $jail/etc/named;
(cd /etc/named; tar cf - * ) | tar xvf -

For secondaries, allow named to create data files:
chmod 770 $jail/etc/named;

2. or DNS data in /var/named (my preference)

mkdir -p $jail/var/named;  cd $jail/var/named;
chgrp named $jail/var/named;
(cd /var/named; tar cf - * ) | tar xvf -

Set Jail permissions

Next, set permissions on files, so that root owns files and named can read all files and write some files. And, disable any SUID/SGID files.
The PID file is put in /var/run and not /usr/local, because we don't want the named user to be able to write to /usr/local/etc (and hence named.conf). The location of the PID file is specified in named.conf.

jail=/home/dns
cd $jail

# remove group write from var
chmod -R g-w var;
# remove all write access to opt and usr
chmod -R a-w opt usr

# For secondaries, allow named to create data files:
chown -R root:named $jail/var/named;
chmod 770 $jail/var/named;

# For primaries, allow named to read, but not write data files:
chown -R root:named $jail/var/named;
chmod 750 $jail/var/named;
chmod -R go-w $jail/var/named;

# Create empty log and pid files:
touch var/log/all.log var/run/named.pid;
chown named:named var/log/all.log var/run/named.pid;

# Allow named user/group to write logs and pid files:
chgrp -R named $jail/var/log $jail/var/run;
chmod 770 $jail/var/run $jail/var/log
chmod -R o-rwx $jail/var/run $jail/var/log

# Allow named to access BIND config file:
chgrp named $jail/usr/local/etc;
chown root:named $jail/usr/local/etc/named.conf;
chmod 640 $jail/usr/local/etc/named.conf;
chmod 750 $jail/usr/local/etc;

# Remove SUID or SGID bits, if any exist:
find . -type f -exec chmod ug-s {} \;

See footnote [8] for an example of an "ls -alR" on a production DNS primary.

Edit DNS config file: if the PID or data location has changed from your original installation, then $jail/usr/local/etc/named.conf needs to be adapted (see also the section BIND Configuration Notes).

 


Starting BIND

The chroot environment is set up and BIND is installed, so the current (non-chroot'ed) BIND can be stopped and the new one started.

  1. Set up a tail on the (syslog) logs, to watch BIND activity:
    tail -f local0log | grep server1 The logs may be in /var/adm/messages or on a remote server, depending on your /etc/syslog.conf configuration. In this example, a centralized server collects logs and we look for messages from server1 (my test server).
  2. Stop the existing BIND...
    On Solaris 2.7: kill `pgrep named`
    On Solaris 2.5/6: ps -ef |grep named   then kill the appropriate PID.
  3. Start BIND chroot'ed:
    /usr/sbin/chroot /home/dns /usr/local/sbin/named -u named
  4. Check for errors:
        • in the syslog log
        • do nslookups
        • make sure the secondary can do zone transfers
        • send a HUP signal to named, to ensure that it reloads configuration correctly.
        • Check the domains using the IP-Plus tool [4].
  5. If everything still looks good, change the /etc/rc2.d/S72inetsvc (or equivalent startup file) entries for starting BIND to something like this:

    if [ -f /home/dns/usr/local/sbin/named -a -f /home/dns/usr/local/etc/named.conf ]; then
    /usr/sbin/chroot /home/dns /usr/local/sbin/named -u named;
    echo "Started chroot'ed BIND domain name server."
    fi


Troubleshooting

If you have a problem, a few tips:


Known Problems

rather than:

/usr/sbin/chroot /home/dns /usr/local/sbin/named -u named

One reader (J. S. Townsley) had similar problems, so he replaced ndc with a script:

#!/bin/sh

case "$1" in

  start)

    /etc/rc.d/init.d/named start;

    ;;

  stop)

    /etc/rc.d/init.d/named stop;

    ;;

  restart)

    /etc/rc.d/init.d/named restart;

    ;;

  *)

    /usr/sbin/chroot /chroot/named /usr/sbin/ndc $1

esac


Configuration Notes


Note 1: BIND's Built-in chroot

BIND 8 had its own chroot function, which works by giving named an option "-t" which points to the chroot jail, for example "named -t /home/dns." When BIND starts up, it chroot's to the jail, after processing command line options and before it starts to answer queries. By compiling BIND and installing directly into the jail, all the bind programs will be correctly in place. Since BIND chroot's after reading user/group information, it doesn't need the other /etc and /usr/lib files noted above.

If BIND is set up as described above, it can still be started using this method, for example,
/home/dns/usr/local/sbin/named -t /home/dns -u named

This method is simpler than the general chroot method below, but it does have the disadvantage that we rely on the BIND code to be executed before the chroot is bug-free. Also, a general chroot can be used to "jail" other programs too.
For the moment, I'll continue using the general chroot method described below, and update this article as problems are found/solved. See also the Known Problems section.


Note 2: The BIND Configuration File

The following is an example named.conf with many comments to explain individual features. The file consists of an options section, ACL and server definitions, and Zone data.

acl "trusted-nameservers" {
  localhost;
  193.A.B.C; // my secondary
  193.A.B.D; // another secondary
  X.A.A.A;   // ISP
  X.Y.Z.X;   // NIC for your country                                                    
};

options {        
  directory "/var/named";                       /* /etc/named is also common */
  //forward only;
  // for Internal DNS servers, forward all unknown queries to external servers:
  //forwarders { 193.a.b.c; 193.a.b.d; };
  /* If there is a firewall between you and nameservers you want
   * to talk to, you might need to uncomment the query-source
   * directive below.  Previous versions of BIND always asked
   * questions using port 53, but BIND 8.1 uses an unprivileged
   * port by default.
   */
  query-source address * port 53;
  pid-file "/var/run/named.pid";
  check-names master warn;                  /* default. */
  datasize 20M;
  stacksize 30M;
  statistics-interval 1440; // stats once per day is enough
  transfer-format many-answers; // faster transfers
  version "DNS server"; // hide BIND version

  // The following will restrict transfers for all zones, if enabled:
  // allow-transfer { trusted-nameservers; };
  recursion yes;          // default

  //allow-query { 193.a.b.c/24; };
};
controls { unix "/var/run/ndc" perm 0600 owner 20000 group 20000; };

logging {
  channel syslog_errors {
    // Syslog logging: typically daemon, if we choose local1,
    // some message still go to daemon (bug), so we leave daemon for now .
    syslog daemon;
    //syslog local1; severity info;
  };
  channel file_log {
    file "/var/named/debug.log" versions 3 size 10m; // limit size + count
    severity dynamic; // catch debug messages
    print-category no; // Category unneeded in debug file?
    print-severity yes; print-time yes;
  }
  category default {
    syslog_errors;            // you can log to as many channels
    //default_syslog;          // by default goes to daemon in syslog
  };
  // ignore all "lame server" errors (only do this if none of the lame
  // servers belong to you; otherwise, fix them)
  category lame-servers{ null; };
  //category statistics { null; }; // We don't need stats for this server

  // enable for testing/debugging:
  //category default { file_log; syslog_errors; };
  //category panic { file_log; };
  //category packet { file_log; };
  //category eventlib { file_log; };
  //other categories; queries, cname, config, load, notify, parser,
  //response-checks, security, statistics, update, xfer-in, xfer-out
};

// Example definition of a Primary
zone "mytestdomain.com" {
  type master;
  file "mytestdomain.com";
  allow-query    { any; };      // no restriction on queries
  allow-update   { none; };    // don't allow dynamic updates
  allow-transfer { trusted-nameservers; }; // restrict zone transfers
};

// Example definition of a secondary
zone "mytestdomain2.com" {
  type slave;
  file "mytestdomain2.com";
  masters          { A.B.C-D };  // IP address of the primary
  allow-query    { any; };
  allow-update   { none; };
  allow-transfer { trusted-nameservers; };
};

// if you get servers giving bad data, ignore them with:
//server 10.0.0.2 { bogus yes; };

// this is the main file for the domain name server. Each line gives
// the file where is stored the name table for a particular domain.
// named.root can be downloaded from ftp.rs.internic.net/domain

zone "." {
  type hint;
  file "named.root";
};

zone "0.0.127.in-addr.arpa" {
  type master;
  file "db.127.0.0";
};


Note 3: TSIG, Transaction Signatures

BIND provides some new security features in its latest release. Here we examine one: the use of TSIG (transaction signatures) to authenticate zone transfers.

Zone transfers are usually limited to a list of IP addresses (via the ACL mechanism) which correspond to specific DNS servers for a zone. Since only IP addresses are used, this mechanism is open to IP spoofing. BIND 8.2 and later allow authentication and verification of zone data. A key is configured on primary and secondary name servers and used to sign messages exchanged between the servers. It's important that the server times are synchronized. If the transfer is not authenticated with the correct key, no zone transfer may take place.

Let's look at an example where we use TSIG to restrict the zone transfers between a DNS primary "prim" (IP address 10.1.1.2) and DNS slave secondary "sec1" (IP address 10.1.2.2).

a) Generate an MD5 key, which will be used as a shared secret between the DNS servers. The "dnskeygen" tool is used. The key is written to a file.

# /usr/local/sbin/dnskeygen -H 128 -h -n prim-sec1.
Generating 128 bit HMAC-MD5 Key for prim-sec1.
Generated 128 bit Key for prim-sec1. id=0 alg=157 flags=513 

# cat Kprim-sec1.+157+00000.private

Private-key-format: v1.2

Algorithm: 157 (HMAC)

Key: bFs2bXnLTYTI7r0WJv7HMA==

b) Create an identical key entry on both servers in named.conf:

key prim-sec1 {

	algorithm hmac-md5;

	secret "bFs2bXnLTYTI7r0WJv7HMA==";

};

c) Add an ACL on both servers to limit transfers to specific hosts, for example:

acl "my-nameservers" {

	localhost;

	10.1.1.2;

	10.1.2.2;

};

d) For each host in the ACL, tell the BIND which key to use (do this for each server), for example on the primary:

server 10.1.2.2 {

  transfer-format many-answers;

  keys { prim-sec1 ; };

};

zone "mytestdomain.com" {

  type master;

  file "mytestdomain.hosts";

  allow-query    { any; };

  allow-update   { none; };

  allow-transfer { my-nameservers; };

}

d) Restart both named servers (send a HUP signal), then check the (syslog) logs for errors.

Testing if it works:

So it's really not difficult to significantly increase the security of your zone transfers. It is important that the file permissions on named.conf be restrictive so that it cannot be read by everyone on a system. The secret string used in the key must remain secret.


Note 4: More tips

allow-recursion { 193.a.b.c/24; };

To stop recursion completely (e.g. on a deligate server), set the option:

recursion no;

In the same vein, bind can be prevented from automatically resolving name server names in NS or RDATA records by setting the option:

fetch-glue no;


Footnotes

  1. BIND Home Page - http://www.isc.org/products/BIND
  2. How to Break Out of a chroot() Jail - http://www.bpfh.net/simes/computing/chroot-break.html
    Creating a Basic Padded Cell - http://www.sunworld.com/swol-01-1999/swol-01-security.html
  4. IP-Plus provides a tool for remotely checking your DNS configuration - http://www.ip-plus.net/tools/dns_check_set-en.html
    Note: to get correct results, allow zone transfer to the IP address 164.128.36.54.
  5. DNS and BIND, 3rd Edition, Paul Albitz & Cricke Liu, published by O'Reilly & Associates.
    A great reference work.
  6. RFC2845: Secret Key Transaction Authentication for DNS (TSIG) - community.roxen.com/developers/idocs/rfc/rfc2845.html
  7. YASSP Solaris Hardening Tool - http://www.yassp.org
  8. An example of an "ls -alR" on a production chroot'ed DNS primary, to show what the file permissions should look like - http://www.boran.com/security/sp/solaris/bind_perms.txt
  9. This article has been translated into Italian by Michel Morelli
    Rafforzare il DNS server BIND
    http://www.ziobudda.net/Recensioni/vedi_recensione.php?ff=7
  10. Running the BIND9 DNS Server securely
    A newer follow-on to this article
    bind9_20010430.html


References

Solaris

Linux:

Other BIND articles

General DNS articles

BIND 9 is hot off the press:

Bind for NT links:

Dents, an alternative DNS server, still in alpha - http://www.dents.org

djbdns is a collection of Domain Name System tools, http://cr.yp.to/djbdns.html, that includes several components:

Acknowledgments

Useful tips were also provided by FOCUS-SUN@SECURITYFOCUS.COM members, including C.M. Wong, Eric Jon Rostetter, J. S. Townsley, Wyman Eric Miles, and Colin Stefani. Fabrice Bacchella pointed out how to use BIND's inbuilt chroot function. See also the archive of Focus-Sun messages. Thanks also to Stephane Grundschober, Kurt Seifried, Matthias Andree and Jason Chan.

About the Author

Seán Boran is an IT security consultant based in Switzerland and the author of the online IT Security Cookbook. He has over 4 years experience managing DNS servers.

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Changes to this article (Doc ID 192, coverstory20001002.html)

02.Jul.00   sb Chroot BIND 8 and publish in the Solaris Digest
10.Sep.00 sb TSIG tested and publish in the Solaris Digest
29.Sep.00 sb Complete rewrite to general Installing & hardening BIND document. Published.
06.Oct.00 sb Minor formatting, note on dig vs. nslookup, link to Bindv9 interview, delete sentance on Bind9 root exploit, it is not true.
13.Nov.00 sb Add note on hiding version information.
14.Dec.00 sb Improvements after feedback and secondary problems. Publish.
08.Jan'00 sb Add link to ripe Guide. Reorganise references. See changes in Green in www.boran.com/security/sp/changelog/bind_hardening_01feb2001.html
08.Mar'01 sb Note on GNU make, Set Jail permissions
30.Mar'01 Add into note on different BIND versions.
04.May.'01 Refer to new BIND9 article
07.Aug'01 Change /usr/ucb/chown to /usr/bin/chown