Official Nmap Project Guide to Network. Discovery and Security Scanning. Gordon "Fyodor" Lyon. From port scanning basics for novices to the type of packet. About this book. Nmap Network Scanning is the official guide to the Nmap Security Scanner. From explaining port scanning basics for novices to detailing. Identifies. UDP. Ports. TCP SYN Scan. -sS. YES. YES. NO. TCP connect() Scan. - sT. NO. YES. NO. FIN Stealth Scan. -sF. YES. YES. NO. Xmas Tree Stealth.

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Get started port scanning with this Nmap tutorial. The installation steps in this guide are for an Ubuntu Linux based system but could be applied with minor. Nmap has a multitude of options and when you first start playing with this excellent tool it can be a bit daunting. In this cheat sheet you will find a. Nmap. Cheat Sheet v! POCKET REFERENCE GUIDE. SANS Institute http:// surlongporetpia.tk Target Specification. IPv4 address: IPv6 address.

Full details of the command and the background can be found on the Sans Institute Blog where it was first posted. Helps in quickly identifying what the HTTP service that is running on the open port. Note the http-enum script is particularly noisy. It is similar to Nikto in that it will attempt to enumerate known paths of web applications and scripts. This will inevitably generated hundreds of HTTP responses in the web server error and access logs.

It will detect the presence of the well known Heartbleed vulnerability in SSL services. Uses ASN, whois and geoip location lookups. Remote Scanning Testing your network perimeter from an external perspective is key when you wish to get the most accurate results. By assessing your exposure from the attackers perspective you can validate firewall rule audits and understand exactly what is allowed into your network. This is the reason we offer a hosted or online version of the Nmap port scanner.

To enable remote scanning easily and effectively because anyone who has played with shodan. Additional Resources The above commands are just a taste of the power of Nmap. As a memory aid, port scan type options are of the form -sC, where C is a prominent character in the scan name, usually the first. The one exception to this is the deprecated FTP bounce scan -b.

By default, Nmap performs a SYN Scan, though it substitutes a connect scan if the user does not have proper privileges to send raw packets requires root access on Unix or if IPv6 targets were specified.

Of the scans listed in this section, unprivileged users can only execute connect and FTP bounce scans. SYN scan is the default and most popular scan option for good reasons. It can be performed quickly, scanning thousands of ports per second on a fast network not hampered by restrictive firewalls. It is also relatively unobtrusive and stealthy since it never completes TCP connections. It also allows clear, reliable differentiation between the open, closed, and filtered states.

This technique is often referred to as half-open scanning, because you don't open a full TCP connection. You send a SYN packet, as if you are going to open a real connection and then wait for a response. If no response is received after several retransmissions, the port is marked as filtered. The port is also marked filtered if an ICMP unreachable error type 3, code 1, 2, 3, 9, 10, or 13 is received. This is the case when a user does not have raw packet privileges or is scanning IPv6 networks.

Instead of writing raw packets as most other scan types do, Nmap asks the underlying operating system to establish a connection with the target machine and port by issuing the connect system call. This is the same high-level system call that web browsers, P2P clients, and most other network-enabled applications use to establish a connection. Rather than read raw packet responses off the wire, Nmap uses this API to obtain status information on each connection attempt.

When SYN scan is available, it is usually a better choice. Nmap has less control over the high level connect call than with raw packets, making it less efficient. The system call completes connections to open target ports rather than performing the half-open reset that SYN scan does.

Not only does this take longer and require more packets to obtain the same information, but target machines are more likely to log the connection. A decent IDS will catch either, but most machines have no such alarm system. Many services on your average Unix system will add a note to syslog, and sometimes a cryptic error message, when Nmap connects and then closes the connection without sending data.

Truly pathetic services crash when this happens, though that is uncommon. An administrator who sees a bunch of connection attempts in her logs from a single system should know that she has been connect scanned. This is a mistake, as exploitable UDP services are quite common and attackers certainly don't ignore the whole protocol. Fortunately, Nmap can help inventory UDP ports.

UDP scan is activated with the -sU option. For some common ports such as 53 and , a protocol-specific payload is sent, but for most ports the packet is empty.. The --data-length option can be used to send a fixed-length random payload to every port.

If an ICMP port unreachable error type 3, code 3 is returned, the port is closed. Other ICMP unreachable errors type 3, codes 1, 2, 9, 10, or 13 mark the port as filtered.

Occasionally, a service will respond with a UDP packet, proving that it is open. If no response is received after retransmissions, the port is classified as open filtered. This means that the port could be open, or perhaps packet filters are blocking the communication.

Version detection -sV can be used to help differentiate the truly open ports from the filtered ones. A big challenge with UDP scanning is doing it quickly. Open and filtered ports rarely send any response, leaving Nmap to time out and then conduct retransmissions just in case the probe or response were lost.

Closed ports are often an even bigger problem. They usually send back an ICMP port unreachable error. ICMP port unreachable messages by default. Linux and Solaris are particularly strict about this. For example, the Linux 2. Nmap detects rate limiting and slows down accordingly to avoid flooding the network with useless packets that the target machine will drop.

Unfortunately, a Linux-style limit of one packet per second makes a 65,port scan take more than 18 hours. Ideas for speeding your UDP scans up include scanning more hosts in parallel, doing a quick scan of just the popular ports first, scanning from behind the firewall, and using --host-timeout to skip slow hosts.

This technique is often referred to as half-open scanning, because you don't open a full SCTP association. You send an INIT chunk, as if you are going to open a real association and then wait for a response. These three scan types even more are possible with the --scanflags option described in the next section exploit a subtle loophole in the TCP RFC [8] to differentiate between open and closed ports.

These three scan types are exactly the same in behavior except for the TCP flags set in probe packets. If a RST packet is received, the port is considered closed, while no response means it is open filtered. The port is marked filtered if an ICMP unreachable error type 3, code 1, 2, 3, 9, 10, or 13 is received. The key advantage to these scan types is that they can sneak through certain non-stateful firewalls and packet filtering routers.

Another advantage is that these scan types are a little more stealthy than even a SYN scan. Don't count on this though-most modern IDS products can be configured to detect them. The big downside is that not all systems follow RFC to the letter.

A number of systems send RST responses to the probes regardless of whether the port is open or not. This causes all of the ports to be labeled closed. This scan does work against most Unix-based systems though.

Another downside of these scans is that they can't distinguish open ports from certain filtered ones, leaving you with the response open filtered. This scan is different than the others discussed so far in that it never determines open or even open filtered ports. It is used to map out firewall rulesets, determining whether they are stateful or not and which ports are filtered.

When scanning unfiltered systems, open and closed ports will both return a RST packet. Nmap then labels them as unfiltered, meaning that they are reachable by the ACK packet, but whether they are open or closed is undetermined. Ports that don't respond, or send certain ICMP error messages back type 3, code 1, 2, 3, 9, 10, or 13 , are labeled filtered. Window scan is exactly the same as ACK scan except that it exploits an implementation detail of certain systems to differentiate open ports from closed ones, rather than always printing unfiltered when a RST is returned.

On some systems, open ports use a positive window size even for RST packets while closed ones have a zero window. So instead of always listing a port as unfiltered when it receives a RST back, Window scan lists the port as open or closed if the TCP Window value in that reset is positive or zero, respectively.

This scan relies on an implementation detail of a minority of systems out on the Internet, so you can't always trust it.

Systems that don't support it will usually return all ports closed. Of course, it is possible that the machine really has no open ports.

If most scanned ports are closed but a few common port numbers such as 22, 25, 53 are filtered, the system is most likely susceptible.


Occasionally, systems will even show the exact opposite behavior. If your scan shows 1, open ports and three closed or filtered ports, then those three may very well be the truly open ones. The Maimon scan is named after its discoverer, Uriel Maimon.. He described the technique in Phrack Magazine issue 49 November Nmap, which included this technique, was released two issues later. However, Uriel noticed that many BSD-derived systems simply drop the packet if the port is open.

Truly advanced Nmap users need not limit themselves to the canned scan types offered. The --scanflags option allows you to design your own scan by specifying arbitrary TCP flags.. Let your creative juices flow, while evading intrusion detection systems. The order these are specified in is irrelevant. That base type tells Nmap how to interpret responses. For example, a SYN scan considers no-response to indicate a filtered port, while a FIN scan treats the same as open filtered.

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Nmap will behave the same way it does for the base scan type, except that it will use the TCP flags you specify instead. If you don't specify a base type, SYN scan is used.

The advantage of this scan type is that it is not as obvious a port scan than an INIT scan. This advanced scan method allows for a truly blind TCP port scan of the target meaning no packets are sent to the target from your real IP address. Instead, a unique side-channel attack exploits predictable IP fragmentation ID sequence generation on the zombie host to glean information about the open ports on the target.

IDS systems will display the scan as coming from the zombie machine you specify which must be up and meet certain criteria. Besides being extraordinarily stealthy due to its blind nature , this scan type permits mapping out IP-based trust relationships between machines.

The port listing shows open ports from the perspective of the zombie host. So you can try scanning a target using various zombies that you think might be trusted. You can add a colon followed by a port number to the zombie host if you wish to probe a particular port on the zombie for IP ID changes.

Otherwise Nmap will use the port it uses by default for TCP pings Yet it still uses the -p option to select scanned protocol numbers, reports its results within the normal port table format, and even uses the same underlying scan engine as the true port scanning methods.

So it is close enough to a port scan that it belongs here. Besides being useful in its own right, protocol scan demonstrates the power of open-source software. While the fundamental idea is pretty simple, I had not thought to add it nor received any requests for such functionality. Then in the summer of , Gerhard Rieger. I incorporated that patch into the Nmap tree and released a new version the next day. Few pieces of commercial software have users enthusiastic enough to design and contribute their own improvements!

Protocol scan works in a similar fashion to UDP scan. Instead of iterating through the port number field of a UDP packet, it sends IP packet headers and iterates through the eight-bit IP protocol field. The headers are usually empty, containing no data and not even the proper header for the claimed protocol.

A proper protocol header for those is included since some systems won't send them otherwise and because Nmap already has functions to create them.

If Nmap receives any response in any protocol from the target host, Nmap marks that protocol as open. An ICMP protocol unreachable error type 3, code 2 causes the protocol to be marked as closed Other ICMP unreachable errors type 3, code 1, 3, 9, 10, or 13 cause the protocol to be marked filtered though they prove that ICMP is open at the same time. If no response is received after retransmissions, the protocol is marked open filtered -b FTP relay host FTP bounce scan.

This allows a user to connect to one FTP server, then ask that files be sent to a third-party server. Such a feature is ripe for abuse on many levels, so most servers have ceased supporting it. One of the abuses this feature allows is causing the FTP server to port scan other hosts. Simply ask the FTP server to send a file to each interesting port of a target host in turn.

The error message will describe whether the port is open or not. This is a good way to bypass firewalls because organizational FTP servers are often placed where they have more access to other internal hosts than any old Internet host would.

Nmap supports FTP bounce scan with the -b option. It takes an argument of the form username:password server:port. As with a normal URL, you may omit username:password, in which case anonymous login credentials user: anonymous password:-wwwuser are used. The port number and preceding colon may be omitted as well, in which case the default FTP port 21 on server is used.

This vulnerability was widespread in when Nmap was released, but has largely been fixed. Vulnerable servers are still around, so it is worth trying when all else fails. If bypassing a firewall is your goal, scan the target network for port 21 or even for any FTP services if you scan all ports with version detection and use the ftp-bounce. NSE script. Nmap will tell you whether the host is vulnerable or not. If you are just trying to cover your tracks, you don't need to and, in fact, shouldn't limit yourself to hosts on the target network.

Before you go scanning random Internet addresses for vulnerable FTP servers, consider that sysadmins may not appreciate you abusing their servers in this way. Port Specification And Scan Order In addition to all of the scan methods discussed previously, Nmap offers options for specifying which ports are scanned and whether the scan order is randomized or sequential.

By default, Nmap scans the most common 1, ports for each protocol. This option specifies which ports you want to scan and overrides the default. Individual port numbers are OK, as are ranges separated by a hyphen e. So you can specify -p- to scan ports from 1 through Scanning port zero. For IP protocol scanning -sO , this option specifies the protocol numbers you wish to scan for The qualifier lasts until you specify another qualifier.

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If no protocol qualifier is given, the port numbers are added to all protocol lists. Ports can also be specified by name according to what the port is referred to in the nmap-services.

Be careful about shell expansions and quote the argument to -p if unsure. Ranges of ports can be surrounded by square brackets to indicate ports inside that range that appear in nmap-services. For example, the following will scan all ports in nmap-services equal to or below -p [].

Be careful with shell expansions and quote the argument to -p if unsure. Specifies that you wish to scan fewer ports than the default. Normally Nmap scans the most common 1, ports for each scanned protocol. With -F, this is reduced to Nmap needs an nmap-services file with frequency information in order to know which ports are the most common. If port frequency information isn't available, perhaps because of the use of a custom nmap-services file, -F means to scan only ports that are named in the services file normally Nmap scans all named ports plus ports By default, Nmap randomizes the scanned port order except that certain commonly accessible ports are moved near the beginning for efficiency reasons.

This randomization is normally desirable, but you can specify -r for sequential sorted from lowest to highest port scanning instead. Using its nmap-services. This lookup is usually accurate-the vast majority of daemons listening on TCP port 25 are, in fact, mail servers.

However, you should not bet your security on this! People can and do run services on strange ports.. When doing vulnerability assessments or even simple network inventories of your companies or clients, you really want to know which mail and DNS servers and versions are running. Having an accurate version number helps dramatically in determining which exploits a server is vulnerable to. Version detection helps you obtain this information.

The nmap-service-probes. Nmap tries to determine the service protocol e. Of course, most services don't provide all of this information. Some UDP ports are left in the open filtered state after a UDP port scan is unable to determine whether the port is open or filtered.

Version detection will try to elicit a response from these ports just as it does with open ports , and change the state to open if it succeeds. Note that the Nmap -A option enables version detection among other things. When Nmap receives responses from a service but cannot match them to its database, it prints out a special fingerprint and a URL for you to submit if to if you know for sure what is running on the port.

Please take a couple minutes to make the submission so that your find can benefit everyone. Version detection is enabled and controlled with the following options: -sV Version detection. Enables version detection, as discussed above. Alternatively, you can use -A, which enables version detection among other things. This behavior can be changed by modifying or removing the Exclude directive in nmap-service-probes, or you can specify --allports to scan all ports regardless of any Exclude directive.

When performing a version scan -sV , Nmap sends a series of probes, each of which is assigned a rarity value between one and nine.

The lower-numbered probes are effective against a wide variety of common services, while the higher-numbered ones are rarely useful.

The intensity level specifies which probes should be applied. The higher the number, the more likely it is the service will be correctly identified. However, high intensity scans take longer. The intensity must be between 0 and The default is When a probe is registered to the target port via the nmap-service-probes ports directive, that probe is tried regardless of intensity level.

This ensures that the DNS probes will always be attempted against any open port 53, the SSL probe will be done against , etc. This is a convenience alias for --version-intensity 2.

This light mode makes version scanning much faster, but it is slightly less likely to identify services. An alias for --version-intensity 9, ensuring that every single probe is attempted against each port. This causes Nmap to print out extensive debugging info about what version scanning is doing. It is a subset of what you get with --packet-trace. This method works in conjunction with the various port scan methods of Nmap. Thus you can effectively obtain the same info as rpcinfo -p even if the target's portmapper is behind a firewall or protected by TCP wrappers.

Decoys do not currently work with RPC scan.. This is automatically enabled as part of version scan -sV if you request that. As version detection includes this and is much more comprehensive, -sR is rarely needed. Each fingerprint includes a freeform textual description of the OS, and a classification which provides the vendor name e. Sun , underlying OS e. Solaris , OS generation e.

If Nmap is unable to guess the OS of a machine, and conditions are good e. By doing this you contribute to the pool of operating systems known to Nmap and thus it will be more accurate for everyone. OS detection enables some other tests which make use of information that is gathered during the process anyway. This measures approximately how hard it is to establish a forged TCP connection against the remote host.

It is useful for exploiting source-IP based trust relationships rlogin, firewall filters, etc or for hiding the source of an attack.

This sort of spoofing is rarely performed any more, but many machines are still vulnerable to it. The actual difficulty number is based on statistical sampling and may fluctuate. It is generally better to use the English classification such as "worthy challenge" or "trivial joke". This is only reported in normal output in verbose -v mode. Most machines are in the "incremental" class, which means that they increment the ID field in the IP header for each packet they send.

This makes them vulnerable to several advanced information gathering and spoofing attacks.

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Another bit of extra information enabled by OS detection is a guess at a target's uptime. The guess can be inaccurate due to the timestamp counter not being initialized to zero or the counter overflowing and wrapping around, so it is printed only in verbose mode.

Enables OS detection, as discussed above. Alternatively, you can use -A to enable OS detection along with other things. OS detection is far more effective if at least one open and one closed TCP port are found.

Set this option and Nmap will not even try OS detection against hosts that do not meet this criteria. This can save substantial time, particularly on -Pn scans against many hosts. It only matters when OS detection is requested with -O or -A. When Nmap is unable to detect a perfect OS match, it sometimes offers up near-matches as possibilities. The match has to be very close for Nmap to do this by default. Either of these equivalent options make Nmap guess more aggressively.

Nmap will still tell you when an imperfect match is printed and display its confidence level percentage for each guess.

When Nmap performs OS detection against a target and fails to find a perfect match, it usually repeats the attempt. By default, Nmap tries five times if conditions are favorable for OS fingerprint submission, and twice when conditions aren't so good.


Specifying a lower --max-os-tries value such as 1 speeds Nmap up, though you miss out on retries which could potentially identify the OS. Alternatively, a high value may be set to allow even more retries when conditions are favorable. This is rarely done, except to generate better fingerprints for submission and integration into the Nmap OS database. It allows users to write and share simple scripts using the Lua programming language [11] , Tasks we had in mind when creating the system include network discovery, more sophisticated version detection, vulnerability detection.

NSE can even be used for vulnerability exploitation. To reflect those different uses and to simplify the choice of which scripts to run, each script contains a field associating it with one or more categories. Currently defined categories are auth, default. Scripts are not run in a sandbox and thus could accidentally or maliciously damage your system or invade your privacy.

Never run scripts from third parties unless you trust the authors or have carefully audited the scripts yourself. Performs a script scan using the default set of scripts.

Some of the scripts in this category are considered intrusive and should not be run against a target network without permission. Runs a script scan using the comma-separated list of filenames, script categories, and directories. Each element in the list may also be a Boolean expression describing a more complex set of scripts. Each element is interpreted first as an expression, then as a category, and finally as a file or directory name.

The special argument all makes every script in Nmap's script database eligible to run. The all argument should be used with caution as NSE may contain dangerous scripts including exploits, brute force authentication crackers, and denial of service attacks. File and directory names may be relative or absolute. Absolute names are used directly.

When a directory name is given, Nmap loads every file in the directory whose name ends with. All other files are ignored and directories are not searched recursively.

When a filename is given, it does not have to have the.

When referring to scripts from script. The argument to --script had to be in quotes to protect the wildcard from the shell. More complicated script selection can be done using the and, or, and not operators to build Boolean expressions. The operators have the same precedence [12] as in Lua: not is the highest, followed by and and then or. You can alter precedence by using parentheses. Because expressions contain space characters it is necessary to quote them.

It loads all scripts that are in the default category or the safe category or both. Lets you provide arguments to NSE scripts. To include one of these characters in a string, enclose the string in single or double quotes.

A backslash is only used to escape quotation marks in this special case; in all other cases a backslash is interpreted literally. A table may contain simple string values or more name-value pairs, including nested tables. This option does what --packet-trace does, just one ISO layer higher. If this option is specified all incoming and outgoing communication performed by a script is printed. The displayed information includes the communication protocol, the source, the target and the transmitted data.

Specifying --packet-trace enables script tracing too. It is only necessary to update the database if you have added or removed NSE scripts from the default scripts directory or if you have changed the categories of any script. This option is generally used by itself: nmap --script-updatedb. Timing And Performance One of my highest Nmap development priorities has always been performance. A default scan nmap hostname of a host on my local network takes a fifth of a second. That is barely enough time to blink, but adds up when you are scanning hundreds or thousands of hosts.

Moreover, certain scan options such as UDP scanning and version detection can increase scan times substantially. So can certain firewall configurations, particularly response rate limiting.

While Nmap utilizes parallelism and many advanced algorithms to accelerate these scans, the user has ultimate control over how Nmap runs. Expert users carefully craft Nmap commands to obtain only the information they care about while meeting their time constraints. Techniques for improving scan times include omitting non-critical tests, and upgrading to the latest version of Nmap performance enhancements are made frequently.

Optimizing timing parameters can also make a substantial difference. Those options are listed below. Some options accept a time parameter. This is specified in seconds by default, though you can append 'ms', 's', 'm', or 'h' to the value to specify milliseconds, seconds, minutes, or hours.

So the --host-timeout arguments ms, , s, and 15m all do the same thing. Nmap has the ability to port scan or version scan multiple hosts in parallel.

Nmap does this by dividing the target IP space into groups and then scanning one group at a time. In general, larger groups are more efficient. The downside is that host results can't be provided until the whole group is finished. So if Nmap started out with a group size of 50, the user would not receive any reports except for the updates offered in verbose mode until the first 50 hosts are completed. By default, Nmap takes a compromise approach to this conflict. It starts out with a group size as low as five so the first results come quickly and then increases the groupsize to as high as The exact default numbers depend on the options given.

When a maximum group size is specified with --max-hostgroup, Nmap will never exceed that size. Specify a minimum size with --min-hostgroup and Nmap will try to keep group sizes above that level. Nmap may have to use smaller groups than you specify if there are not enough target hosts left on a given interface to fulfill the specified minimum.

Both may be set to keep the group size within a specific range, though this is rarely desired.

These options do not have an effect during the host discovery phase of a scan. This includes plain ping scans -sn. Host discovery always works in large groups of hosts to improve speed and accuracy. The primary use of these options is to specify a large minimum group size so that the full scan runs more quickly. A common choice is to scan a network in Class C sized chunks.And if it gets a response back, Nmap doesn't even need to worry about the IP-based ping packets since it already knows the host is up.

Step 1a: Host Discovery with well knows ports nmap -PS,80,88,,,,,,, -T4 -oA hostdiscovery The lack of response could also mean that a packet filter dropped the probe or any response it elicited.

The higher the number, the more likely it is the service will be correctly identified. Repeatability Zenmap's command profiles make it easy to run the exact same scan more than once.

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