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Hide DNS Software Version

Sometimes a new vulnerability is found in DNS software and script kiddies are scanning the Internet to exploit unpatched systems. It’s a best practice to hide software version on your DNS servers, although this is not a real protection it just makes a little harder to find your servers via scanning.

Use dig command to find which version is running on your name servers:

$ dig +short @ns1.example.com version.bind txt chaos
"9.8.2rc1-RedHat-9.8.2-0.23.rc1.el6_5.1"

Bind

To hide version in when using Bind, open named.conf configuration file using your favorite editor, go to options section and set a custom version string using version option.

Example:

// /etc/named.conf
options {
  // Hide bind version
  version "unknown";
};

Restart the server (use bind9 instead of named on systems based on Debian):

$ sudo service named restart
Stopping named: .                                          [  OK  ]
Starting named:                                            [  OK  ]

Verify that server is returning new version string:

$ dig +short @ns1.example.com version.bind txt chaos
"unknown"

Knot

Edit knot.conf and set version parameter in system section to off:

system {
  # Used for answer to CH TXT 'version.server' or 'version.bind'
  version off;
}

Restart the server to apply changes:

$ sudo service knot restart
Stopping knot: .                                          [  OK  ]
Starting knot:                                            [  OK  ]

MyDNS

TODO

NSD

Edit nsd.conf configuration file and set hide-version parameter to yes in server section.

server:
  # /etc/nsd/nsd.conf
  # Don't answer VERSION.BIND and VERSION.SERVER CHAOS class queries
  hide-version: yes

Restart NSD server:

$ sudo service nsd restart
Stopping nsd:                                              [  OK  ]
Starting nsd:                                              [  OK  ]

PowerDNS

Edit /etc/pdns/pdns.conf and set version-string to anonymous then restart PowerDNS server.

version-string=anonymous

TinyDNS

TinyDNS doesn’t expose version.

Microsoft DNS

To control how the server responds to version query, use dnscmd command with EnableVersionQuery parameter. Possible values:

  • 0x00000000 (DNS_VERSION_QUERY_OFF) No version information will be returned.
  • 0x00000001 (DNS_VERSION_QUERY_FULL) The server responds with major operating system version, minor operating system version, and operating system revision.
  • 0x00000002 (DNS_VERSION_QUERY_MINIMAL) The server responds with major operating system version and minor operating system version.

Example:

dnscmd /config /EnableVersionQuery 0

On Windows Server 2008 and Windows Server 2008 R2, the default value is 0x00000001. On Windows Server 2012 and Windows Server 2012 R2, the default value is 0x00000000.

YADIFA

Yadifa version can be hidden setting version in main section:

<main>
  version "not disclosed"
</main>

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