Questions tagged [tcp]

Transmission Control Protocol (TCP) is a transport layer protocol that provides a connection-oriented data stream service with guaranteed, in-order delivery.

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Setting the CWR TCP Flag in a Hping Command

I am trying to set the CWR flag when doing a hping command to another machine. I can set all the other flags, (Eg -S, -F etc) but I can't find any example of the CWR flag. I've checked Man Pages and ...
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Suricata TCP/UDP reassembled stream [on hold]

I want to obtain reassembled stream payload for both TCP and UDP in Suricata. How can i obtain stream data by manipulating the source code? Which methods/classes in the source can provide me the ...
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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 ...
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Is TCP Sequence Bruteforcing dangerous nowadays?

I was reading about TCP sequence prediction which is described as almost impossible on all updated Operating System nowadays. The total amount of possible sequence numbers is 2^32-1 which, if we try ...
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firewall behaviour

If a client connects to a server he will start listening for the response on some random high port number. The client then expects any packet destined for that port to be a valid answer. Or does he ...
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4answers
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Add SSL on top of existing TCP connection

This may sound as basic question for some but I have never done such thing. Imagine I basically have simple TCP client implemented on C# (e.g. TCPClient class) and simple TCP server implemented using ...
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DNS and sometimes TCP packet are being sent out upon disconnecting and connecting wifi connection [on hold]

I am monitoring my network interface and noticed that I can reproduce a behavior where some cryptic DNS packets are being sent out as well as TCP sometimes, without me opening any browser or ...
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TCP Sack panic proof of concept?

For the vulnerability called TCP SACK panic([1], [2], [3], and many more): is there a proof of concept code out there that can be used to test vulnerability status and effectiveness of remedies? [1] ...
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Secure preshared key 2 way authentication

I have the following setup: A server and a client will be connected over tcp. The server and client both have access to the preshared secret key. When the client connects to the server, the client and ...
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Whether the `resets received for embryonic SYN_RECV sockets` and `invalid SYN cookies received` shows attacks there?

In my CentOS, I use netstat -s to check my CDN node server network summary. [root@hkk10 ~]# netstat -s Ip: 26529370 total packets received 6121 with invalid addresses 0 forwarded 0 ...
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Encrypt and Authenticate localhost-traffic?

I have some app-components on the same machine but in different languages which need to communicate. I am using socket communication over localhost to do so. The data transferred is confidential. ...
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Intercept TCP traffic using Python

Situation: I am trying to intercept TCP (not HTTP) traffic on a Windows machine using Python. I am posting this question as most answers I was able to find teaches how to sniff traffic. Normal ...
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Can I blindly trust 127.0.0.1?

On my system (Ubuntu Server 18.04, if that matters) I have two servers. They are behind a Nginx reverse proxy (i.e. accessing service.mywebsite.com internaly proxies the request to 127.0.0.1:...
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What ports are okay to be open on a macbook pro?

When I do a network scan for open ports on my MacBook Pro, I can see the following open TCP ports below. Are these 'standard' open port for a personal computer of this type? Should I be concerned? ...
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Pros and cons of disabling TCP timestamps

So, lynis informs me that I should unset net.ipv4.tcp_timestamps. I know that's a bad thing because an attacker could figure out which updates that require restarting the machine I haven't applied, or ...
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Weird attack making my server CPU super high

I noticed that my server CPU is super high and the reason is grep "A" command After a deep look, that what I've found in my active internet connections list (netstat -tupn) tcp 0 0 ...
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Tor relay on port 9001 TCP

I executed netstat -t on my linux terminal and noticied a tor relay running on port 9001. I've search about the IP address of relay on shodan and got a result that address is from Russia, after that i ...
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Connection changes after waking from sleep

On Debian, Linux, I am using netstat to monitor connections. After waking my system from sleep, I noticed a change in one of the connections, using port 6667 for irssi (identified by PID). I like to ...
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What are the risks of exposing the Docker for Windows daemon on localhost?

A developer running Docker for Windows needs to enable the option "Expose daemon on tcp://localhost:2375 without TLS" in Docker setting > General tab. There is a warning: Exposing daemon on TCP ...
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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 ...
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NMAP - Closed vs Filtered

A lot of people seem to ask this question, as there are a bunch of posts about it; however I feel like none truly answer the question (that I have found). I want to understand why NMAP decides to ...
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Any Known countermeasures against clock skew fingerprinting?

I know lots of websites that do clock skew fingerprinting using tcp timestamps. I know how to disable timestamps but i want to know techniques that can be used to counter clock skew fingerprinting. I ...
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Router Security Log Shows Many Blocked TCP Connections

When checking my router tonight I looked at its security log. I saw thousands of blocked tcp traffic. Why are these considered security events? The log shows many blocked tcp incoming request from ...
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Sniffing TCP packets using Wireshark

I am trying to reverse engineer a decoder. To do so I need to sniff the packets that the decoder receives from an Android application installed on my phone, this application is what controls the ...
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1answer
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TCP Hijacking and conflicting data handling on the OS level

Assuming I perform a TCP hijacking attack, by having access to the wire on which packets are being transmitted. In practice, the party to which I'm sending the hijack packet is going to receive the ...
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Question about hping3, TCP and ngrok

I have set up a experimental setup which consists of: Windows PC with ethernet cable; Arduino shield (connected to Windows machine with USB) with LTE connectivity sending data using TCP/IP to ngrok; ...
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How to set reverse tcp connection when doing pentesting in VMs?

msfconsole is a cool opensource pentesting tool from metasploit. Once the exploit is valid, we can set payload to the victim. For persistent connection, we may need meterpreter. But we often test ...
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Honeypot detection: How is TCP/IP implemented on honeypots?

I'm currently studying how to do honeypot detection and was wondering if a possible lead is to analyse how honeypots implement their TCP/IP protocol. I've been looking through the source code for a ...
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Can a hacker hack into port 80?

We normally say port 80 is firewall friendly. But can a hacker just hack into port 80 via TCP or UDP? Or is Port 80 by default not always open? It waits for the host to initiate a connection via ...
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228 views

Websocket connection spoofing

I have a websocket server, where client credentials get validated upon connecting and are never bothered again, since connections are stored in memory. I was wondering, a TCP connection is basically ...
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132 views

Determine victim of port scan's OS

I am taking part in a practice sandbox, and have a pcap file in Wireshark: with the traffic depicting a Vertical Port Scan. Is there anyway to find out the "victim"'s Operating System? The packets are ...
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What do DoS/ DDoS TCP SYN Floods and Layer 7/HTTP floods look like on a firewall log?

I am looking for some examples of log files for DoS or DDoS attacks that show a SYN Flood or a HTTP/Layer 7 Flood. I have had a google, but can't seem to find anything. Would the incoming packet ...
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Any limitaion of clnt_call() in RPC communication?

I have a RPC server and RPC client. Am generating a secure key on client side using TPM1.2 chip. When i run my program for few times everything works fine. But When i run for many times then key is ...
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Confirming a tcp connection is encrypted not just encoded? [duplicate]

This is a follow up of this question. The accpeted answer suggest using tcpdump -A -c 200 but leaves up the crucial part on how to distinguish whether the data is encrypted and not encoded. What I'm ...
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239 views

XMAS Scan vs Inverse TCP

Whats the difference between a XMAS Tree scan and an Inverse TCP scan using the FIN, URG, and PSH flags? Are they the same thing? XMAS Tree scans are designed to manipulate the PSH, URG and FIN flags ...
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Black-box fuzzing a TCP Port running an unknown applicaiton

I'm looking for any guidance around testing a service I've found running on a target server. I'm doing a 'black-box' pen-test and the company is one of those 'I-don't-want-to-tell-you-anything' types ...
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OSSEC, what is it telling me about port changes?

I've been diving into OSSEC for the last couple of months, but I feel unclear on one of it's alerts. I've provided the alert below. The main difference I see in previous output and current output is ...
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28 views

Why do processes on servers have socket types associated to the port number? [closed]

Why do some servers have TCP/UDP alongside the port they're listening to. To my understanding TCP and UDP are socket layers, they're methods of determining how the traffic is being sent over the ...
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OS fingerprinting via TCP

I have searched online about this topic and the only information I got is that TCP SYN/ACK can be used to know the type of the target OS. If that is true, I don't understand how this occurs? Does TCP ...
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2answers
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Nmap not following redirect when using “http-title” script

I am trying to scan a bunch of IPs for their http-title. Now the problem I have is that nmap pretty much never follows any redirects. Usually the title I want is behind that redirect though. For ...
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IOT secure data transfer

I have a question about a monitoring software architecture. Think about 50 different locations in different cities. Assume that these locations are small plants. In every location there are ...
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Is it possible to send HTTP packet via spoofed IP?

I have the following PHP code that writes accepted to a file named text.txt only if the IP is equal to 127.0.0.1 (loopback). If the IP doesn't match it writes denied. <?php $file = fopen('text.txt'...
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1answer
615 views

How to pass a localhost check for an incoming request?

I'm trying to send a request to an http server hosted on a machine. The http server is in C# and drops any packets that are not from localhost: public void Request(HttpListenerContext context) { ...
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TCP protocol Denial-of-service attack [closed]

There are different types of DDoS attacks. As defined by TechTarget, Network-centric or volumetric attacks overload a targeted resource by consuming available bandwidth with packet floods. Protocol ...
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1answer
108 views

MQTT without TLS - prevent publish messages from unauthenticated devices

I have an use case where I'm not able to use MQTTS/TLS due to constraint on devices. Our plan is to perform authentication during MQTT CONNECT, passing a JWT token as a password. If I understand ...
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2answers
762 views

Beginner > Medium > Advanced Books/Guides/Tutorials on TCP/IP [closed]

I am a long time web developer looking to get into infosec. I was hoping to get guidance on material from a beginner's stance on TCP/IP and hopefully "networks". I realise the massive generalisation ...
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SegmentSmack exploit

I am studying about SegmentSmack vulnerability. As far as I understood, the vulnerability is due to the fact the reordering the packets in the out-of-order buffer is a very CPU intensive operation. So ...
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1answer
636 views

Injecting a TCP packet into existing connection

let's see a scheme: and I would like to consider two cases: All IP addresses are public, a cloud is symbol for the Inernet. The first one The H has an established TCP connection: C = (210.10.10....
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How can Insertion attack ever work and fool an IDS on a TCP connection?

An IDS can accept a packet that an end-system rejects. An IDS that does this makes the mistake of believing that the end-system has accepted and processed the packet when it actually hasn't. An ...
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1answer
447 views

Could an attacker spoof a whitelisted IP to access the network?

There is a network that is protected with a firewall and only one IP is whitelisted. Assuming the attacker knows the whitelisted IP, what would prevent an attacker from sending traffic via a spoofed ...