Questions tagged [ports]

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

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76
votes
9answers
20k views

Is it theoretically possible to deploy backdoors on ports higher than 65535?

Assuming you were able to modify the OS/firmware/device for server/client to send and listen on ports higher than 65535, could it be possible to plant a backdoor and have it listen on, say, port 70000?...
46
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5answers
15k views

Should I close port 80 forever and ever since the 2018 Google-indicated web-security initiatives?

I often establish Ubuntu-LAMP environments on which I host a few Drupal web applications that I myself own (I don't provide any hosting services and never done so in the past). Whenever I establish ...
36
votes
4answers
36k 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 ...
36
votes
2answers
42k 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 ...
33
votes
1answer
7k views

I have found ports on my Samsung smart tv running a display service. What can I do with it? [closed]

I have a Samsung Smart TV running Tizen OS, and out of curiosity I scanned it with Nmap. I found multiple open ports. One of those ports is running a "display" service. Does this mean it can cast its ...
29
votes
5answers
10k 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 ...
29
votes
4answers
19k 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 ...
28
votes
9answers
17k views

Is it safer to use a port other than 21 for FTP?

Usually (as far as I know), FTP uses port 21. Since this port is used for FTP so often, is it safer to use another port? My guess is that if someone with malicious intentions tries to break FTP ...
27
votes
1answer
4k views

Why is it better to use ports 20 and 53 as source ports when portscanning?

I read that if a server is inside a DMZ behind a stateless firewall, it is a good idea to use ports 20 and 53 as source ports when conducting port scanning. Why is this a good idea? I guess the ...
25
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3answers
5k views

How wise is it to use a tool for portspoofing at your server to confuse attackers?

I came across this tool recently https://github.com/drk1wi/portspoof How efficient will it be to use it to confuse hackers doing port scanning? If it's actually going to be pretty efficient, why ...
22
votes
2answers
46k 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 ...
20
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6answers
36k 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 ...
16
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2answers
84k 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 ...
14
votes
2answers
6k 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 ...
13
votes
7answers
18k 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 ...
13
votes
4answers
14k 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 ...
12
votes
2answers
3k views

Tons of vulnerabilities are found on tcp/0 port using vulnerability scanners

Performed credentialed Vulnerability scan on linux/Unix servers by Nessus and thousand of vulnerability came out of port tcp/0. How could a IANA reserved port(tcp/0) handle traffic? Are those ...
10
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2answers
18k 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?
10
votes
1answer
8k 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. ...
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 ...
8
votes
2answers
3k 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 ...
8
votes
6answers
14k 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? ...
8
votes
4answers
23k 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 5000/...
8
votes
2answers
20k 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 ...
8
votes
1answer
2k views

Nmap - Intense vs Quick result

I inherited a small network and currently am assessing its security performance. I started port scanning a host (lets call it Weirdo) in that small network and from my perspective, it seems that that ...
8
votes
1answer
7k views

Connection to ports 2000 and 5060 successful despite filtering

I run my own (Ubuntu based) router and have iptables configured to drop all incoming packets by default. To my surprise, running an nmap scan (from the WAN side) shows two open ports related to VOIP: ...
8
votes
3answers
1k 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 ...
7
votes
1answer
5k views

What are non-standard ports and protocols [closed]

I am new to the security field and reading about how to check if an application is secure. One of the checks involves finding out if the app uses non-standard security ports and protocols. However, ...
7
votes
1answer
711 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
2answers
4k 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 ...
7
votes
2answers
3k 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 ...
7
votes
2answers
5k 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 ...
7
votes
1answer
17k views

Why are some ports reported as closed by nmap?

I was scanning a machine from inside the same LAN which is running and up to date Windows XP Home Edition which I suspect may be running some malware. The target machine has an up to date antivirus ...
7
votes
3answers
6k views

Nessus Port scan Vs NMAP Port scan

My objective is to find network vulnerabilities. I have used Nessus and NMAP both for vulnerability scan. I have to verify if I can use only "Nessus" rather than using "NMAP". According to my ...
7
votes
1answer
2k 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 ...
6
votes
4answers
18k views

Is there a nmap command to get the top # most common ports?

I understand nmap by default scans the top 1k 'most common' ports (-F reduces to 100) I understand it gets these 'most common' ports based on the nmap-services file, specifically the frequency (3rd ...
6
votes
6answers
30k 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 ...
6
votes
2answers
13k 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" ...
6
votes
1answer
3k 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 ...
6
votes
3answers
6k 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 ...
6
votes
3answers
8k 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 3389/...
6
votes
1answer
57 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 ...
6
votes
2answers
6k views

Using Nmap to Scan Port Forwarding?

I have enabled port forwarding on my router to do some testing with Nmap. The internal IP address 10.0.0.10 on port 4245 is being sent to my public IP address on port 4245. I can access this with x.x....
5
votes
2answers
6k 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 ...
5
votes
3answers
2k 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
2answers
5k 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. ...
5
votes
3answers
20k 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 ...
5
votes
1answer
634 views

Hardening/Security considerations for torrent clients

I am running Synology's DSM torrent client on a NAS. As I have to (?) open and forward one UDP port for DHT and another one (UDP/TCP) for data transmission I am exposing myself to threats originating ...
5
votes
2answers
1k views

Samba open ports, not being filtered

nmap scan of my ubuntu computer, output when ran with -sV: 139/tcp open netbios-ssn Samba smbd 3.X (workgroup: MEDIAPC) 445/tcp open netbios-ssn Samba smbd 3.X (workgroup: MEDIAPC)...
5
votes
1answer
3k 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 ...