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Network Penetration conducted a survey at the start of 2003 to check the status of the UK's DNS infrastructure. The second scan of the year has just been completed and the results are much more positive. There are however still some serious holes in major areas...Here is a look at what was tested, the results, some sample zone transfers and recommendations.

What Was Tested

During each scan only one test was performed against each domain:

A full zone transfer (axfr) against the first authoritive DNS server assigned to that domain.

A zone transfer consists of copying the contents of a zone file from a DNS server. This normally occurs when a secondary DNS server wishes to replicate the information for a zone from a primary DNS server for purposes of backup/redundancy. A zone file consists of all the information about that zone such as the IP address of a web server or mail server or possibly the hostname and IP of a firewall. Much of the information is open to request such as what email server is used for that domain, but other records such as the IP address and domain name of the firewall should not be open.

First and second level zones generally do not contain IP addresses of firewalls and such like, but they do contain huge lists of every subdomain. Take for example the zone file for the co.uk domain, it would contain every domain with a co.uk extension.

Example Zone Transfers

All the transfers were conducted using free online tools provided by demon.net

EXAMPLE 1: Secured Domain

A zone transfer from the .biz domain returns in a timeout and no information is returned.

EXAMPLE 2: Secured Domain

Where as when trying to zone transfer .mil a connection refused is returned.

Domain: mil.
Primary Nameserver: G.ROOT-SERVERS.NET
E-mail Contact: HOSTMASTER@NIC.mil 

/www/cgi-bin/demon/external/bin/dig @G.ROOT-SERVERS.NET mil. axfr 

; <<>> DiG 2.1 <<>> @G.ROOT-SERVERS.NET mil. axfr ; (1 server found)
;; Received 0 records.
;; FROM: nu7www.demon.net to SERVER: 192.112.36.4 ;; WHEN: Tue Aug 12 01:08:14 2003 

EXAMPLE 3: Unsecure Domain

An unsecured domain however such as fake.com would return the following:

Domain: fake.com.
Primary Nameserver: ns1.fakehosting.com E-mail Contact: admin@fakehosting.com 

/www/cgi-bin/demon/external/bin/dig @ns1.fakehosting.com fake.com. axfr 

; <<>> DiG 2.1 <<>> @ns1.netincomehost.com fake.com. axfr ; (1 server found)
fake.com.3600SOAns1.fakehosting.com. admin.fakehosting.com. ( 
        10; serial
        3600; refresh (1 hour)
        600; retry (10 mins)
        1209600; expire (14 days)
        3600 ); minimum (1 hour)

        fake.com. 3600 A        1.2.3.4
        fake.com. 3600 NS       ns1.fakehosting.com
        fake.com. 3600 NS       ns2.fakehosting.com
        fake.com. 3600 MX10     smtp.fake.com.

        webmail.fake.com. 3600 CNAME webmail.freemail.com.
        cisco.fake.com. 3600 A  1.2.3.1
        fw1.fake.com. 3600 A    1.2.3.2
        snort.fake.com. 3600 A  1.2.3.3
        www.fake.com. 3600 A    1.2.3.4
        ftp.fake.com. 3600 A    1.2.3.5
        pdc.fake.com. 3600 A    1.2.3.6

        fake.com. 3600 SOA      ns1.fakehosting.com admin.fakehosting.com. (
                10; serial
                3600; refresh (1 hour)
                600; retry (10 mins)
                1209600; expire (14 days)
                3600 ); minimum (1 hour)

;; Received 10 records.
;; FROM: nu7www.demon.net to SERVER: 64.42.224.9 ;; WHEN: Mon Aug 11 23:20:47 2003 

The fictitious zone file for fake.com shows a whole range of possible targets that a hacker could use to quickly map a network without having to send hardly any packets to the network.

The information regarding the top and second level domains are not being published due to the possibility of them being exploited at some point in the future.

Results for UK DNS Infrastructure

At the start of the year nearly all the second level domains in the UK allowed a zone transfer, but now its only sections of the government lagging behind.

Domain          Transfer Possible    Number of Records    Notes
                Jan 03   August 03   Jan 03  August 03

uk              Yes      yes         220     248
ac.uk           no       no          -       -
bl.uk           Yes      no          1892    -
co.uk           no       no          -       -
gov.uk          yes      no          5       -
govt.uk         no       no          -       -
ltd.uk          yes      no          26723   -            Over 1 Mb
me.uk           yes      no          57329   -            Over 1 Mb
mod.uk          yes      yes         1484    1729
net.uk          yes      no          1298    -
nls.uk          yes      no          438     -
org.uk          yes      no          422265  -            Over 20 Mb
plc.uk          yes      no          3646    -
police.uk       yes      yes         234     241
sch.uk          yes      no          71360   -            Over 1 Mb

The only test performed against each server was a full zone transfer; some returned the full zone file while others such as gov.uk only returned a partial zone file.

In total 15 domains were tested, 3 passed the test with transfers not possible at the start of the year compared to 12 in August — 20% at the start of the year and 80% in August. Can the UK score a 100% by the end of the year and lock down all their DNS servers? One would like to think so.

After sending an early copy of this report to various domain administrators, Network Penetration received a response from Jay Daley, Director of IT at Nominet UK.

"It is our policy that .uk is not closed to zone transfers though all of the second level domains (SLDs) that we manage are. There are a large number of people who pull the .uk zone to allow their nameservers fast repudiation of non-existent SLDs (e.g. when someone types in xxx.com.uk by accident)."

The two remaining zones mod.uk and police.uk may be open for a specific reason unknown to Network Penetration at this time but upon initial inspection they appear to be unsecured DNS servers. One possible reason is that zone transfers are extremely useful for debugging problems with domain name servers.

The information provided in this report does not necessarily mean that each domain was unsecured/secured but merely gives a rough guide to the state of the UK's DNS infrastructure.

Recommendations

Zone files contain lots of crucial information that a hacker or terrorist could use to attack a nations infrastructure due to zone files containing information on a networks design and also highlighting key nodes within a networks infrastructure. Zone transfers should be blocked and not allowed from untrusted hosts such as those from the general public. Disallowing zone transfers from hosts other than your backup DNS servers, still allow hostnames to be resolved.

By Steve Jones. Visit the blog maintained by Steve Jones here.

Related topics: DNS, Domain Names