Home arrow Site Administration arrow Page 3 - Webserver Security (Part I)

Dumping a zone using nslookup - Administration

This first article in a two-part series deals with tools to find security holes in webservers and workstations. Some of the topics covered are: port scanning, finding NFS security holes, and using lsof.

  1. Webserver Security (Part I)
  2. The server offers services it was not intended to
  3. Dumping a zone using nslookup
  4. Other Helpful Tools
  5. rpcinfo query to www.example.server
  6. Remote SNMP queries
By: Kristian Kohntopp
Rating: starstarstarstarstar / 2
April 19, 2000

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To get a listing of all known hosts in a domain you could run nmap scan against the complete network containing the server of interest. Alternatively you could look into the DNS and see what the server operator has published about his domain.

Using the example.server domain again:
# nslookup
< set type=ns
< www.example.server.
Server:  ns.provider.net
origin = ns.example.server
mail addr = postmaster.ns.example.server
serial = 2000032201
refresh = 10800 (3H)
retry   = 3600 (1H)
expire  = 604800 (1W)
minimum ttl = 86400 (1D)
< server ns.example.server
Default Server:  ns.example.server
< ls example.server.
$ORIGIN example.server.
@                       1D IN A
wwwtest                 1D IN A
news                    1D IN A
localhost               1D IN A
listserv                1D IN A
igate                   1D IN A
The "set type=ns" (Nameserver) command instructs nslookup to ask only for information about the nameserver of a domain. Our query for "www.example.server." will then return all nameservers for that host, in this case only a single server, "ns.example.server."

We now use the command "server ns.example.server" to direct all further queries directly to that server. With "ls example.server." we ask that particular server for a complete listing of the zone "example.server". We receive a listing of all hostnames and ip numbers published by the operator of example.server.

A better-configured BIND8 allows us to limit zone transfers to known secondary name servers. "ls" commands from arbitrary hosts will be blocked and logged. If a domain has multiple nameservers it is often worthwile to try all of them: While the primary server is often secured, the secondaries are not and will happily list the zone for you.

Security conscious network operators run their internal DNS from a different server than their Internet setup. There is no need to tell the world which machines are running in your offices and how they are named. It is completely sufficient to publish the names and addresses of your production machines.

>>> More Site Administration Articles          >>> More By Kristian Kohntopp

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