Other systems will blank out various pieces some will send back 0 for the current time, for example. If this script is used in conjunction with version detection it can augment the standard nmap version detection information with data that this script has discovered.
Retrieving the name and operating system of a server is a vital step in targeting an attack against it, and this script makes that retrieval easy. Even on systems using a simple counter starting at zero, the counter eventually overflows and wraps around.
With a 1, Hz counter increment rate, the counter resets to zero roughly every 50 days. So a host that has been up for days will appear to have been up only two days. Even with these caveats, the uptime guess is accurate much of the time for most operating systems, so it is printed when available, but only in verbose mode.
The line is also omitted if Nmap cannot discern the timestamp increment rate or it seems suspicious like a year uptime. A side effect of one of the OS detection tests allows Nmap to compute how many routers are between it and a target host. The distance is zero when you are scanning localhost, and one for a machine on the same network segment. Each additional router on the path adds one to the hop count. The Network Distance line is not printed in this example, since Nmap omits the line when it cannot be computed no reply to the relevant probe.
In other words, you can make a full connection to those systems and send but not receive data while spoofing a different IP address. The target's logs will show the spoofed IP, and you can take advantage of any trust relationship between them. This attack was all the rage in the mid-nineties when people commonly used rlogin to allow logins to their account without any password from trusted IP addresses. Kevin Mitnick is alleged to have used this attack to break into Tsutomu Shimomura's computers in December The good news is that hardly anyone uses rlogin anymore, and many operating systems have been fixed to use unpredictable initial sequence numbers as proposed by RFC For these reasons, this line is only printed in verbose mode.
Sadly, many vendors still ship vulnerable operating systems and devices. Even the fixed ones often vary in implementation, which leaves them valuable for OS detection purposes. The class describes the ISN generation algorithm used by the target, and difficulty is a rough estimate of how hard the system makes blind IP spoofing 0 is the easiest. The parenthesized comment is based on the difficulty index and ranges from Trivial joke to Easy , Medium , Formidable , Worthy challenge , and finally Good luck!
While the rlogin family is mostly a relic of the past, clever attackers can still find effective uses for blind TCP spoofing.
For example, it allows for spoofed HTTP requests. The spoofing allows attackers to hide their identity, frame someone else, or exploit IP address restrictions. Many systems unwittingly give away sensitive information about their traffic levels based on how they generate the lowly bit ID field in IP packets. This field describes the ID generation algorithm that Nmap was able to discern.
Note that many systems use a different IP ID space for each host they communicate with. Sometimes on a network it is beneficial to know the Operating System OS of a machine. Accessing a system is easier when you know the OS because you can specifically search the Internet for known security holes in the OS. Granted, security holes are usually patched quickly, but you need to know when a security hole exists.
Scanning your own network to detect the OS types can help you to see what a hacker will be able to see about your network. The database is used when doing OS detection, but it is not automatically updated. The easiest way to manage an update is first to look at the database version number. Open the file in a text editor and the version number is usually listed on the second line. The database version for this file is Joined Apr 11, Messages Reaction score Credits 4, Thanks, Jarret B -- a very good tutorial, for me!
Here is a link that explains how nmap can perform OS detection and the appropriate command syntax. You might find the p0f utility useful for this sort of thing. No OS detection is performed when not using root user, no traceroute either. Yes you will be able to perform -A scan, but only with service discovery, just as you would with -sV flag. Do you have a reference or a source that backs up the claim that "No OS detection is performed when not using root user"?
This is the whole point of the question. Add a comment. Active Oldest Votes. Improve this answer. Lucian Nitescu Lucian Nitescu 1, 9 9 silver badges 23 23 bronze badges. OP asks explicitly for methods that work without admin privileges. I don't know why OP does, but this does not answer the question. My intention to find the OS type without using admin privileges and any passwords. DragonlordDrake DragonlordDrake 2 2 bronze badges.
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