Nmap, besides being a powerful port scanner, also has the capability to determine the specific version of a service that is running on a remote host. This feature is known as Service Version Detection. Service version detection enables Nmap to extract valuable information about the specific versions of services and applications that are running on hosts.
To perform service version detection, Nmap sends a series of probes to the target ports. Each probe is designed to stimulate a response from a specific type of service which can then be used to identify the service and its version. Once the responses are received by Nmap, they are compared with a database of service and application signatures to identify the specific versions of services running on the target.
Nmap’s service version detection can provide the users with valuable knowledge about potential vulnerabilities which could be exploited. For example, a service like Apache HTTP Server may be running an older version which is known to have specific security vulnerabilities. By using Nmap’s service version detection, a user can identify the version of Apache running on a host and investigate known vulnerabilities that could potentially be exploited.
Service version detection is done using the “-sV” option in Nmap. Here’s an example:
```
nmap -sV targetHostnameOrIP
```
The output will include a list of all open ports on the target, along with the service type and version running on each.
Service detection is not a trivial task due to the varying behavior of respective services and protocols. Hence, Nmap’s service detection does not just rely on one method, but instead uses several techniques like banner grabbing, NULL probe, Generic catch-all, Probe-response comparison, etc.
It’s important to note that while service version detection can provide valuable knowledge about possible vulnerabilities, it may also increase the scan time and the chance of detection by intrusion detection systems (IDS), as it involves extra network traffic and irregular packets.
For comprehensive and detailed information on Nmap service detection, The Nmap Network Scanning book is a valuable resource, specifically Chapter 7 that focuses on service and application version detection. The official Nmap website and documentation also provide in-depth knowledge on its various features.
References:
1. Lyon, Gordon F. (2009). Nmap Network Scanning: The Official Nmap Project Guide to Network Discovery and Security Scanning. Insecure, p. 131.
2. “Nmap.” Nmap – Free Security Scanner For Network Exploration & Security Audits, nmap.org.
3. “Nmap – Service and Application Version Detection.” Nmap, nmap.org/book/vscan.html
