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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Does TCP/IP protocol offer a reliable way of determining who the actual sender was?

So I'm just poking around the TCP/IP protocol using a Ruby library called PacketFu, and it seems to me that in each packet, it is possible to set all of the following Source IP Destination IP Source ...
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4answers
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What security mechanisms are used in BGP and why do they fail?

I just read about Indosat trying to take over the Internet by mistake. I read on a Polish infosec-related website that most of their announced routes failed to propagate, but some of them reach the ...
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How does “traceroute over TCP” work, what are the risks, and how can it be mitigated?

There is a utility called tcptraceroute, and this enhancement called intrace that is used just like a standard traceroute, but it works over TCP. How is the syn flag in TCP used to achieve ...
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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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Is it possible to pass TCP handshake with spoofed IP address?

Little time ago, me and my friends argued if TCP handshake can be passed with a spoofed IP address. Assume I have a https web server that allows only admin's IP numbers. Can anyone connect that web ...
11
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Does HTTPS encryption on a site prevent the NSA from knowing you visited its domain / the URL?

The reason I ask whether HTTPS protects the metadata of your Internet activity from a wiretapping entity on the backbone like the NSA or not, is the following scenario: Say I am browsing the ...
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6answers
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Is blocking UDP and TCP sufficient to prevent unwanted network activity?

I want to be 100% sure that my machine only connects where and when I want it to. If I use a firewall that blocks all UDP and TCP packets but those that I explicitly allow to pass, can I be 100% sure ...
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How can I explain to the client that rfc2385 TCP MD5 Checksums can't be turned on for linux webservers?

I've had a long running conversation with a client where they perform a Rapid7 security scan which then warns about TCP MD5 checksums missing on port 80. This is what I think I know: RFC 2385 was ...
8
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Once established, are sockets on localhost secure?

Once a TCP socket has been established on localhost, and a connection made using accept, is it possible for a non-privileged user to intercept or modify bytes sent over this connection, or can this ...
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Spoof IP adress after a TCP handshake

I know it is not possible to perform a successful TCP Handshake with a spoofed IP-Address. However I wonder: Is it possible to spoof the IP once a TCP handshake was performed successfully? For ...
7
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TCP Sequence Prediction and it's prominence in modern systems/networks

I have a question regarding your experience of TCP Sequence Prediction that I am hoping someone could help with. I am aware of how TCP Sequence Prediction works and how the connection can be hijacked ...
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138 views

Why do ISPs allow faked source IP addresses?

Ok so apparently you can specify a source IP when doing a SYN request or something. Besides just asking why in the world that would even be allowed, I will move past that because I want to understand ...
7
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170 views

If two programs on the same machine communicate through TCP, can it be seen from the outside?

Assume there are two programs running on the same computer at the same time. The computer is connected to a LAN. The two programs communicate via a TCP socket, and the socket is opened using the IP ...
6
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1answer
180 views

Are there any situations when one can only mount a passive MITM?

This came up while discussing Web & insecure HTTP - Using RSA for encrypting passwords on the client side Is there any such situation possible when requesting an HTTP page where an attacker is ...
6
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3answers
81 views

Can a TCP connection be terminated by an attacker if SSL/TLS has been used to protect data in the TCP segment?

I understand that SSL/TLS is built on top of TCP. That is after a TCP connection is established, an SSL handshake can be started. When it is completed, all communication will be encrypted and ...
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How could a SYN flood affect a home router

I was curious how a DoS attack would affect a home router. In particular, I'm interested in how a SYN flood would affect a home router. The reason I'm interested is due to a Cisco document I read. ...
5
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How are ACK storms created and what's a good mitigation strategy for them?

The context is network based load balancers. It would be nice if someone could explain how TCP ACK storms are generated in real life and practical mitigation strategies for them. Edit: Clarification ...
5
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465 views

Can you sniff traffic to ip address from outside of your network?

I am not sure what it is called or even if it is possible but here is the scenario I am curious about: I login to a site that does not use SSL/TLS to do some work (unfortunately I must use this site ...
5
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1answer
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Retrieving client certificate using Tcpdump results in zero length certificate

I am trying to proxy a mobile app (with Fiddler), which sends a client certificate to the server it connects to. I would think that capturing traffic with Tcpdump, retrieving the client certificate ...
4
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1answer
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Why is the server returning 3 SYN + ACK packets during a SYN scan?

When you do a SYN scan against a opened TCP port (not filtered by Firewall), the server normally returns 3 SYN + ACK packets. So, why 3 of that? The target server is a Linux machine if relevanted ...
4
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3answers
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Secure communication between two applications on the same system

I'm writing a software which is divided into two separate stand-alone pieces. One is a service like application that handles all the logics, the other one is a GUI application that just works as a ...
4
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2answers
104 views

Is encryption possible for simplex (one-directional) TCP/IP, and if so, how?

As explained in the TCP/IP Guide, it is possible to configure TCP/IP to operate in simplex mode and this mode is utilized, among other things, in communication from satellites. One consideration with ...
4
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1answer
270 views

Do concurrent connections to an HTTPS website perform separate SSL handshakes?

I know that most browsers nowadays support around 6 concurrent TCP sessions per hostname, to perform multiple requests at the same time. For sites which utilise SSL, is there a separate handshake ...
4
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1answer
413 views

Security implications for two applications communicating with TCP/IP on localhost

Considering this for the local loopback connection: - It is implemented entirely within the operating system's networking software and passes no packets to any network interface controller. If ...
4
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1answer
218 views

Block this DDoS attack

since more than a week my dedicated server (located at ovh.com) has been under TCP SYN (I think) attack, ovh don't care about it but this attack is killing my server with a high CPU load (permanent ...
4
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1answer
289 views

Explain the last part of how Mitnick hacked Tsutomu Shimomura with an IP sequence attack

I was reading up on why TCP ISNs need to be randomized, which led me to this write up by Tsutomu Shimomura. I understood how IP address spoofing and predicting the ISN helped the attacker establish a ...
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3answers
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Multiple SSL connections in a single HTTPS web request

I set up Apache2 with SSL and tried to request the default Apache2 web page ("It works!") using https://[IP_ADDRESS]. The Chrome developer tool shows that only one HTTP connection is established, ...
4
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1answer
158 views

Protect password/authenticating during transit over (insecure) TCP socket for a game

Background I am designing a multi-player game with a single server that handles multiple worlds. Each player logs into the server initially before requesting which world to join. The server has a ...
4
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1answer
226 views

Why does my web server receive so many TCP resets from some clients?

I run a web server and log connections that are dropped. Occasionally, I get a burst of TCP RST packets from some of my clients, like this: Feb 11 11:56:29 SRC=1.2.3.4 TTL=57 SPT=38383 DPT=80 ...
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186 views

Malware / vulnerability that uses or causes malformed IP or TCP Headers

I'm curious if there are any examples of malformed IP or TCP headers (for example, checksums that don't match, reserved bits that aren't zero, or poor header length numbers) used by malware, or that ...
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Stopping DDOS TCP SYN and UDP flood attacks

I would like to know if it's possible to stop a TCP SYN OR ICMP Flood attacks if these attacks are detected at time. What is the most accurate process to filter these addresses if the only way is to ...
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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 ...
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903 views

TCP versus UDP resilience to DDoS

I am building a service that I can implement equally well with either TCP or UDP. If I use TCP, I expose vulnerability to SYN flood and other attacks on TCP protocol. If I use UDP, it will be harder ...
3
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3answers
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FIN Attack- What is this type of attack really?

I just wanted to know what exactly is the FIN attack. I know about the FIN flag that is used to indicated the closing of a connection via TCP. But what exactly is FIN attack?
3
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2answers
106 views

Should I block outbound TCP RST (on closed ports)?

I have a range of inbound TCP ports open on the firewall, but usually closed on the host machine. I see a handful of unknown connection attempts each day, for which the server returns TCP RST. I ...
3
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1answer
127 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 ...
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2answers
265 views

Authenticating AD user over TCP socket

I have a server that communicates with clients over a .NET socket. I want the server to authenticate the connection in an SSO kind of style by checking that the current user is in a certain group. ...
3
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1answer
377 views

How is the TLS protected against length field of the header being modified?

I know this question looks very silly, but, it has been bothering me for a while and I am unable to come up with an answer by myself. So, here it goes.. Packets in the TLS protocol consist of a 5 ...
3
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1answer
499 views

Is it possible to force client use TCP instead UDP for DNS queries?

Assume I am managing a firewall between DNS server and clients. Is there any way to force clients use TCP rather than UDP, so we can prevent DNS spoof types of DDoS attacks?
3
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1answer
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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 ...
3
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1answer
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Expose web service in a secure manner

Requirement I have a web service I need to expose on the DMZ for external communication. The web service communicates directly with a critical database that sits on an internal net. Current ...
3
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2answers
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When should I drop a packet with ICMP type 3, code 9 or 10, TCP RST, or TCP ACK?

This answer says there are a few ways of dealing with a blocked packet at a firewall: At each of these levels a 1st IP packet (and any other protocol packet as an ESP or AH packet) might receive ...
3
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1answer
834 views

What is DDOS TCP KILL?

I've recently been introduced to Kali Linux's webkiller tool, located in the websploit category. It works on the concept of Tcpkill. I don't understand how the DoS attack with Tcpkill works. Can ...
3
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1answer
132 views

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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3answers
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Is there an alternative to TCP/IP that encrypts end-to-end?

If there was a communication protocol that encrypts at the very low-level, this would solve the problem of wiretapping entirely and for all.
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Firewall & TCP Traffic

I have a question regarding network firewalls and TCP traffic. When a firewall rule is set to block either inbound traffic, outbound traffic, or both on a port, does that only apply to initial ...
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2answers
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Any way to circumvent a 'filtered' response on NMap?

I know that a filtered response on NMap means that the firewall dropped the packets or that NMap just didn't receive a response, but is there any way to circumvent this? Is it possible that the ...
2
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2answers
230 views

Protecting against GCHQ port scans: How does TCP stealth work?

Today I read the first time about a draft of TCP Stealth which should serve as a protection against GCHQ and NSA vulnerability scanning(Source: https://en.wikipedia.org/wiki/TCP_Stealth): The ...
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2answers
198 views

Does NTP leak local system time?

As I understand the paper An Improved Clock-skew Measurement Technique for Revealing Hidden Services (6/23 = pdf page 3), it implies that a NTP client leaks the system's local time because of TCP ...
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2answers
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Sending Syslog/SNMP information over the internet using standard UDP port 514

I'm looking into monitoring a Windows VPS by sending Syslog messages to a Synology NAS, which can generate email alerts and such. I also would like to use SNMP to generate health stats, and see trends ...