Nmap dns-cache-snoop NSE Script


This page contains detailed information about how to use the dns-cache-snoop NSE script. For list of all NSE scripts, visit the Nmap NSE Library.

Select:
Overview
Error Messages

Script Overview

Script source code: https://github.com/nmap/nmap/tree/master/scripts/dns-cache-snoop.nse
Script categories: intrusive, discovery
Target service / protocol: dns, udp
Target network port(s): 53
List of CVEs: -

Script Description

The dns-cache-snoop.nse script 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.

Dns-cache-snoop NSE Script Arguments

This is a full list of arguments supported by the dns-cache-snoop.nse script:

dns-cache-snoop.domains

An array of domain to check in place of the default list.

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.

- - -
To use these script arguments, add them to the Nmap command line using the --script-args arg1=value,[arg2=value,..] syntax. For example:

nmap --script=dns-cache-snoop --script-args dns-cache-snoop.domains=value,dns-cache-snoop.mode=value <target>

Dns-cache-snoop NSE Script Example Usage

Here's an example of how to use the dns-cache-snoop.nse script:

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

Dns-cache-snoop NSE Script Example Output

Here's a sample output from the dns-cache-snoop.nse script:

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

Dns-cache-snoop NSE Script Example XML Output

There is no sample XML output for this module. However, by providing the -oX <file> option, Nmap will produce a XML output and save it in the file.xml file.

Author

  • Eugene V. Alexeev

References

See Also

Related NSE scripts to the dns-cache-snoop.nse script:

Visit Nmap NSE Library for more scripts.

The dns-cache-snoop.nse script may fail with the following error messages. Check for the possible causes by using the code snippets highlighted below found in the script source code. This can often times help in identifying the root cause of the problem.

Error: "%s" is not a known mode. Use "nonrecursive" or "timed".

Here is a relevant code snippet related to the "Error: "%s" is not a known mode. Use "nonrecursive" or "timed"." error message:

220:	  if mode == "nonrecursive" then
221:	    cached = nonrecursive_mode(host, port, domains)
222:	  elseif mode == "timed" then
223:	    cached = timed_mode(host, port, domains)
224:	  else
225:	    return string.format("Error: "%s" is not a known mode. Use "nonrecursive" or "timed".")
226:	  end
227:	
228:	  if #cached > 0 then
229:	    nmap.set_port_state(host, port, "open")
230:	  end

Version

This page has been created based on Nmap version 7.92.

Go back to menu.