This is a text-only version of the following page on https://raymii.org:
---
Title : Hide or determine BIND version number
Author : Remy van Elst
Date : 08-05-2013
URL : https://raymii.org/s/tutorials/Get_DNS_server_version_and_hide_it_in_BIND.html
Format : Markdown/HTML
---
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.
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### 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.][2]. There is also the [HS class, that stands for
Hesiod.][3]
### 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.
[1]: https://www.digitalocean.com/?refcode=7435ae6b8212
[2]: https://en.wikipedia.org/wiki/Chaosnet
[3]: https://en.wikipedia.org/wiki/Hesiod_(name_service)
---
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