9.1 Telnet Session Negotiation

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Telnet session negotiation (TSN) is the simplest way to determine a remote OS. All it requires is that you telnet to the server. It is surprising how many systems have telnet running for no reason. Worse, many networks respond with a banner that gives the exact OS version! Although this method is not elegant, it is nevertheless effective. TSN should be the first thing you check in fingerprinting.

It is worth noting that this weakness is rampant among software makers and is not limited to operating systems. For example, NTMail, a popular POP3 mail server from Gordano, returns the exact version of the software to anyone passing by on the Internet. Simply telnet to the default POP3 port (port 110) on a server running NTMail, and you learn the exact version (and even the owner's key!). This access was provided so that Gordano could troubleshoot and also track piracy of their software. However, with the information it provides, a cracker can do a quick search for exploits for that version (such as the denial-of-service vulnerability affecting early versions of NTMail) and attack with ease. TSN is a classic method, but it is becoming less effective as administrators are learning to turn off their banners (except in programs such as NTMail, where you can't).

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Security Warrior
Security Warrior
ISBN: 0596005458
EAN: 2147483647
Year: 2004
Pages: 211

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