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I would like to know that how vulnerability scanners identify the version of services running on the target after identifying the service by the port number.

  • Do you mean banner grabbing? – jarryd Jan 27 '18 at 20:58
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How Fingerprinting works

For every service fingerprinting would be done differently, generally, it works by finding differences between the implementations, and using them to detect the version of the software, I have included a few simple examples:

SSH

If you run the following command:

nc HOST 22

You can see that the first thing that a server sends is a string identifying it's version, such as:

SSH-2.0-OpenSSH_7.2p2 Ubuntu-4ubuntu2.4

From this you can get the version

HTTP

If you run the following command:

curl -v URL > /dev/null

You can see that the server sends many headers, one of which is likely to look like this:

< Server: cloudflare

This can show you the server if it has not been changed, and possibly the plugins running also

Wordpress

Looking at the feed available at /feed/ gives an xml file with the following tag:

<generator>https://wordpress.org/?v=4.9.2</generator>

If this is disabled then differences in the readme can be used to detect the version instead

  • short answer is: the service tells you what version it is – schroeder Jan 27 '18 at 17:43
  • @jrtapsell Thank you so much for the detailed answer. – hanzalah Feb 1 '18 at 15:47

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