Script `dns-cache-snoop`

Script types: portrule
Categories: intrusive, discovery
Download: https://svn.nmap.org/nmap/scripts/dns-cache-snoop.nse

Script Summary

Performs DNS cache snooping against a DNS server.

There are two modes of operation, controlled by the dns-cache-snoop.mode script argument. In nonrecursive mode (the default), queries are sent to the server with the RD (recursion desired) flag set to 0. The server should respond positively to these only if it has the domain cached. In timed mode, the mean and standard deviation response times for a cached domain are calculated by sampling the resolution of a name (www.google.com) several times. Then, each domain is resolved and the time taken compared to the mean. If it is less than one standard deviation over the mean, it is considered cached. The timed mode inserts entries in the cache and can only be used reliably once.

The default list of domains to check consists of the top 50 most popular sites, each site being listed twice, once with "www." and once without. Use the dns-cache-snoop.domains script argument to use a different list.

Script Arguments

dns-cache-snoop.mode: which of two supported snooping methods to use. nonrecursive, the default, checks if the server returns results for non-recursive queries. Some servers may disable this. timed measures the difference in time taken to resolve cached and non-cached hosts. This mode will pollute the DNS cache and can only be used once reliably.
dns-cache-snoop.domains: an array of domain to check in place of the default list.

Example Usage

nmap -sU -p 53 --script dns-cache-snoop.nse --script-args 'dns-cache-snoop.mode=timed,dns-cache-snoop.domains={host1,host2,host3}' <target>

Script Output

PORT   STATE SERVICE REASON
53/udp open  domain  udp-response
| dns-cache-snoop: 10 of 100 tested domains are cached.
| www.google.com
| facebook.com
| www.facebook.com
| www.youtube.com
| yahoo.com
| twitter.com
| www.twitter.com
| www.google.com.hk
| www.google.co.uk
|_www.linkedin.com

Requires

Author:

Eugene V. Alexeev