In computer networking a port is a software construct serving as a communications endpoint in a computer's host OS.

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32
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4answers
16k views

Is there any meaning in only allowing port 80 and 443 today?

It's become standard fare for security minded organisations to block everything other than 80 and 443. As a result, more and more applications (other than web browsers) are learning to use these ports ...
27
votes
4answers
4k views

How do you deal with massive port scans?

This morning I was looking through firewall logs and saw there were about 500 packets marked as port scan. The scanning range was from 1000-1200 5000-5200. The IP address is 85.25.217.47 which seems ...
25
votes
4answers
11k views

Dangers of opening up a wide range of ports? (mosh)

Why do we generally configure firewalls to filter out all traffic that we don't specifically allow? Is this just an extra layer of security for defense-in-depth that buys us nothing if we are not ...
17
votes
2answers
23k views

What are the security implications of enabling UPnP in my home router?

I found port forwarding entries in home router that I haven't manually configured. Is that because of UPnP? Are applications simply able to tell the router to forward ports on their own? Are there ...
14
votes
2answers
2k views

What's the diff between blocking a port with a firewall and not starting a service on that port in the first place?

I was considering setting up a software firewall (pf) on my web server and did some research on them. Were I to do it, it'd involve basically blocking connections to all ports except 80, 443, and the ...
11
votes
5answers
3k views

Why do hackers scan for open ports?

So, whenever you hear of the mean little hackers who hack websites you hear of "port scanning". I understand what it is (looking for all open ports / services on a remote machine), however that begs ...
11
votes
2answers
43k views

How do hackers take advantage of open ports as a vector for an attack?

It is widespread knowledge, and therefore a common practice, to close open ports on any machines connected to the internet. If for example, a typical program uses port xyz as it's communication ...
10
votes
4answers
11k views

How to listen to all ports (UDP and TCP) or make them all appear open (linux)

I got an external Debian server. The problem is that my university campus doesn't allow connections to go outside when the port is different than TCP port 22, 80, 443, or UDP port 123. I tested them ...
10
votes
1answer
3k views

ports blocked by firewall and not the server

I was asked this question at an interview and i wasn't sure about the answer. The question was "suppose you were checking the open ports on a particular webserver which was behind a firewall, how ...
9
votes
1answer
7k views

GHOST: which services are vulnerable, ssh, web server?

GHOST (CVE-2015-0235) just popped up. GHOST bug: is there a simple way to test if my system is secure? deals with how to find out if your system is vulnerable. exim is mentioned specifically. ...
7
votes
1answer
569 views

different portscan tools give different results

I have different results as of my open TCP ports. When using nmap -sS 127.0.0.1, I get some 5 usual open ports, but when using osx built-in tool as stroke, I get those 5 ports plus 5 extra ports. How ...
7
votes
6answers
4k views

How to bypass Nmap blockage?

I rent a server, and my provider seems to be blocking nmap. Is there any other tools I could use to test my home network from the outside? Also, does blocking nmap on a network provide any security? ...
7
votes
3answers
153 views

Risk of running services on ports >1024

In a Reddit thread on securing SSH access to a Raspberry Pi, one commenter recommended running SSH on a non-standard port of 8123. Another commenter had this to say on the matter: Don't change ...
6
votes
5answers
5k views

Nmap reporting almost every port as open

I have noticed during some assesments when doing a TCP port scan, Nmap will report almost every port as open for a machine. Using for example nmap -sS -PN -T4 target -p0-65535, over 20,000 ports will ...
6
votes
2answers
838 views

How nmap guesses the operating system?

nmap has the capability to guess the operating system with the option -O. I was highly surprised that it can find the correct kernel or service pack. * How nmap guesses the operating system? * What ...
6
votes
1answer
109 views

Exploring unknown service

I'm fairly new to network stuff and currently exploring a Wi-Fi radio device in my home network. In this process I noticed an open port. 58028/tcp open unknown 1 service unrecognized despite ...
5
votes
2answers
1k views

Is it good practice to manually lock down ports on each host

We have a strong perimeter firewall. Would it make sense to still use IPTables on each host to hard block any and all ports except for the ones that are needed (DNS, 80 for the web server, nagios ...
5
votes
2answers
975 views

Why would a stealth scan attract more attention than a connect scan?

I'm reading an Information Security book and am faced with the question: Why may nmap stealth scans(SYN) attract more attention than simple connect scans(TCP connect())? Why might it be?
5
votes
4answers
12k views

Router Ports open

What ports on my home router should be open, say if I'm only using it for browsing the internet. Right now these four are open, 23/tcp open telnet 53/tcp open domain 80/tcp open http ...
5
votes
2answers
1k views

Detect what is running on an open port?

I have a wireless camera in my network. Running nmap on the camera, I discovered that the port 1010 is open but I could not find what it is used for. I looked in the administration pannel and did not ...
5
votes
1answer
48 views

Safely Experimenting With Sockets

I'm learning about TCP/IP and (Berkeley/UNIX) socket programming. Let's say I have two scenarios: 1) I write two programs in C, a client and a server, and bind them each to a non-well-known port on ...
5
votes
1answer
916 views

Firewalk through a Firewall on our subnet

Having trouble firewalking. I am trying to determine all the open ports on my firewall/gateway. Here is my lab network diagram: (Skip to the bottom of the following explanation for a direct list of ...
5
votes
2answers
4k views

How should an outgoing connection white-list be created?

I see my previous question was closed as duplicate of Why block outgoing network traffic with a firewall?. The answers that everyone agree with mention the value of blocking outgoing connections (to ...
4
votes
3answers
4k views

How to figure out which open ports or services are insecure?

We have around one thousand machines on internet. We do port scanning with nmap, and find many ports open on these machines. Sometime we found administrative website using HTTP instead of HTTPS, we ...
4
votes
2answers
2k views

How helpful is rkhunter?

I have a software firewall implemented on my server, and I have closed all unnecessary ports. I have strong passwords, and I validate user input on my website. With these things already in place, do ...
4
votes
4answers
2k views

How can I scan open ports without being traced back

I would like to scan open ports of a server. But as far as I know, when I try to scan the open ports with something like nmap in shell they would be able to trace me. Is there a way to secure this ...
4
votes
3answers
4k views

Which of these ports are safe to leave open, which are not?

I just ran nMap against my IP address and got the following result: PORT STATE SERVICE 21/tcp open ftp 22/tcp open ssh 23/tcp open telnet 80/tcp open http 443/tcp open https ...
4
votes
3answers
2k views

Is there is a way to lock my USB port over the device physically?

Is there is a way to lock my USB port over the device physically ? For example I am connecting the USB mouse and keyboard on an public computer but I do not want anyone to remove them physically. I ...
4
votes
3answers
13k views

Is it really better to use port 80 or 443 for outgoing traffic in order to bypass user firewall?

I recently created a reverse connection shell in C#. I tested it with some computers and I noticed that some computers connected back correctly and I established connection with them but another ...
4
votes
2answers
4k views

Setup of Kali Linux for reverse shell connections over the internet

I am running Kali Linux as a VM on my Windows machine which is NAT'd behind my company network, if I wish to pen test a website for a client and believe that a reverse shell is possible, what is a ...
3
votes
2answers
837 views

How to force nmap to check all the ports?

I heard that nmap scans for only 1000 most common ports while we do server scan. Is it possible to force nmap to check all the ports for scanning? If yes,How?
3
votes
2answers
2k views

Is my ISP doing a port scan on my computer?

I have been logging incoming connections with iptables for a while and I have been observing the following popping up periodically: 11:45:10 my.com kernel: IPTABLES: SRC=220.255.XX.XXY ...
3
votes
4answers
10k views

Exploiting through a filtered port

I'm doing some pentesting against a machine the lecturer set up in the lab. NMAP shows port 445 to be filtered and Nessus confirms the ms08_067 vulnerability is present on that machine. I tried ...
3
votes
3answers
2k views

Why block network ports?

There was another good question here on why you should block outgoing traffic: Why block outgoing network traffic with a firewall? But I was hoping to get an answer on why it is a good idea to block ...
3
votes
2answers
7k views

If a port is closed how come you can still use it?

What does it actually mean for a port to be closed or stealthed? According to tests I've run all my ports (tested) are stealthed but clearly I can still use the internet. Also are the terms "blocked" ...
3
votes
2answers
2k views

Tools/methods helping to determine application/protocol serving specific port

I do blackbox testing of the server and figured out that there is a bunch of listening ports. I need to determine what services/protocols those ports are used for. What I've tried so far is to use ...
3
votes
2answers
2k views

What is the safest way to ssh to a machine behind a router?

I am thinking about forwarding port 22, to 22 on the machine behind router, but is it safe? Anyone can try to connect to my public IP on port 22 and then indefinitely try to guess user and password. ...
3
votes
2answers
8k views

Port scanning legal or not? [closed]

Is port scanning legal ? In which countries ? my option : I think port scanning is like a short-walk( or a long-walk) in the neighbourhood, just curious about neighbours are up to. I think that ...
3
votes
1answer
2k views

How does OS detection work in practice?

I was wondering how OS detection really works on Nmap. I know it is about to send different tcp probes to see how the target machine responds to them. But what kind of probes would distinguish a ...
3
votes
1answer
157 views

Common attacks when no ports are open

If you have a web server with all ports closed (except, of course, the necessary HTTP) what kind of attacks can an attacker use to hack into the system? Are the only vulnerabilities stuff like ...
3
votes
2answers
147 views

Auditing Existing Socket Connection

Is there any way to interact with a program's socket traffic without installing Winpcap? I understand that the one listening program per port is a restriction regarding TCP/IP, but I guess I'm more ...
3
votes
1answer
129 views

Is it possible to find out what a remote user is trying to do connecting to a closed port?

From my iptables log, I can observe a particular remote IP address trying to connect to my server from port 80 to a private port number: Jul 09 01:24:41 example.com kernel: IPTABLES: IN=eth1 ...
3
votes
1answer
5k views

Is opening both TCP/UDP less secured than just TCP or UDP when needed and why?

If application needs opened port X UDP, or X TCP combination. Is there any potential risk by opening both UDP/TCP as I usually am not sure which one the application uses?
3
votes
2answers
864 views

Scanning multiple subnets with nmap to determine open services & ports

First off, I know nmap's documentation is very powerful and I have been reading through it rather extensively. I will be scanning externally, with permission, to determine ports & services that ...
3
votes
1answer
4k views

Security risk of opening port 111 (rpcbind)?

As far as I understood rpcbind is used for listing active services, and telling the requesting client where to send the RPC request. If a host listens on port 111, one can use rpcinfo to get program ...
3
votes
2answers
715 views

How to practically detect current system net traffic?

I know that some viruses or trojans can install rootkits or bootkits to change system's normal behaviour; AFAIK for example filter queries for running processes or even hide active TCP ports. My ...
3
votes
2answers
15k views

Does portforwarding present a risk to anonymity?

AirVPN by default has all ports closed but allows port-forwarding. I think this is required for P2P. Is this a threat to anonymity (e.g. would the person at the other end of the P2P transmission know ...
3
votes
1answer
461 views

What do Msgsrvr and Scientia-ssdb do?

I'm having a task in a computer security class in school where I'm supposed to scan a host for open ports in order to find out what services are being run there. I have found out (among other things) ...
3
votes
2answers
69 views

All ports are unfiltered

I'm currently studying a peneteration/hacking course. I am trying to use nmap against a target to find all the ports that are filtered. I thought if I used an ACK-scan nmap would give me all the ...
3
votes
1answer
216 views

Can the windows Remote Procedure Call subsystem be modified from the default without causing Windows 8/8.1/10 to break?

This is a question that personally as a security professional has bugged me for a long time. So, a default Windows installation, from XP up to 10, typically has a few services listening on the ...