Skip to main content

Raymii.org Raymii.org Logo

Quis custodiet ipsos custodes?
Home | About | All pages | Cluster Status | RSS Feed

Hide or determine BIND version number

Published: 08-05-2013 | Author: Remy van Elst | Text only version of this article


❗ This post is over eleven years old. It may no longer be up to date. Opinions may have changed.

The BIND nameserver (and many others) return their version number when queried a special DNS query. This gives exposure and that is most of the time a bad thing. This tutorial shows you how to query DNS servers for their version and how to stop/change your own BIND server version exposure.

Recently I removed all Google Ads from this site due to their invasive tracking, as well as Google Analytics. Please, if you found this content useful, consider a small donation using any of the options below:

I'm developing an open source monitoring app called Leaf Node Monitoring, for windows, linux & android. Go check it out!

Consider sponsoring me on Github. It means the world to me if you show your appreciation and you'll help pay the server costs.

You can also sponsor me by getting a Digital Ocean VPS. With this referral link you'll get $200 credit for 60 days. Spend $25 after your credit expires and I'll get $25!

Chaos Query

The following DIG and NSLOOKUP queries will show the version of BIND:

A home router queried with DIG:

dig @192.168.1.1 version.bind txt chaos
;; ANSWER SECTION:
version.bind.       0   CH  TXT "dnsmasq-2.47"

A Microsoft DNS server queried with nslookup:

nslookup -type=txt -class=chaos version.bind ns1.metaregistrar.nl
Server:         ns1.metaregistrar.nl
Address:        81.4.97.217#53

version.bind    text = "Served by PowerDNS - http://www.powerdns.com"

What is chaos or CH class you ask? It is/was a network technology, see the wikipedia page for more info.. There is also the HS class, that stands for Hesiod.

Hide it in BIND

When running a BIND nameserver, edit your /etc/bind/named.conf.options file (or the config file where you have your options) and add the following option:

options {
    [...]
    version "Not supported";
}

You can of course put whatever you like in there, for example you can spoof a Microsoft DNS server:

version "Microsoft DNS 6.0.6100 (2AEF76E)";

Or like TransIP does, make it look like your own DNS software:

dig @ns1.transip.nl version.bind txt chaos

;; ANSWER SECTION:
version.bind.       86400   CH  TXT "TransDNS 2.1.1"

Make sure to reload/restart your BIND servers after the change. Do note that you need BIND 8.2 or later for this option to work.

db.bind zone

You can also add a .bind zone, this way your queries will also be logged and you can block possible attempts.

/etc/bind/named.conf.local:

view "chaos" CH {
  match-clients { any; };
  zone "bind" CH {
      type master;
      file "db.bind";
      allow-update { none; };
  };
};

/etc/bind/db.bind:

$TTL    3600
@       86400       CH   SOA     localhost. root.localhost. ( 
                    2013050801      ; serial 
                    3600            ; refresh 
                    3600            ; retry 
                    604800          ; expiry 
                    86400 )         ; minimum 
;  
@                   CH  NS  localhost.

version             CH  TXT "Microsoft DNS 6.0.6100 (2AEF76E)" 
authors             CH  TXT "Raymii.org"

However this gets complicated very fast, you need to wrap all your other zones in views as well:

view "default" IN {
  match-clients { any; };
  [...]
};

So it's better to use the above options file.

Tags: bind , dns , dnsmasq , exposure , named , tutorials , version