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Questions tagged [firewalls]

Concerned with software or hardware firewalls

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4answers
5k views

Best way to push data to a client without being blocked by firewall

I'm asking this question here since I think people on this forum probably have the best knowledge of firewalls and routers. Say I'm designing a multi-player game and I want to push data to the client ...
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4answers
26k views

HTTPS firewall rule

Setting up Firewall rule for HTTPS websites on basic stateless packet filter firewall This seems like a stupid question, but how do I set up a firewall rule to allow HTTPS on a basic packet filter ...
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2answers
1k views

Why are simple packet filter firewalls insufficient for the protection of web applications?

I was wondering why exactly are simple packet filter firewalls insufficient for the protection of web applications?
5
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2answers
171 views

Security concerns allowing internet connected server to write on network server

I don't know much about network engineering since I just started becoming a programmer. The situation is, that my company has a web-interface hosted on one of our servers that is connected to the ...
5
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3answers
481 views

What are the security implications of allowing unlimited size cookies?

Our application firewall blocks requests if it detects a cookie is present with a value greater than 1024 characters in size. Are there any exploits involving large cookies? i.e. How much more ...
5
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2answers
1k views

Security risks of leaving open a VPN connection

We have older firewalls that don't allow for scheduling up/down times of VPN connections, and we're working with a client that will need to connect to it at different times each day. What are the ...
5
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2answers
10k views

What's the difference between an application-level and circuit-level gateway?

From Wikipedia, I understand that circuit level gateways look at TCP handshakes to filter illegitimate traffic and that application level gateways somehow filter application specific traffic. But I ...
5
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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
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1answer
2k views

Can a Cisco ASA 5505 block this DDoS attack?

Since more than a week ago, my dedicated server (located in 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 (...
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4answers
2k views

what is a good public available iptables script for ddos mitigation?

what is a good public available iptables script for ddos mitigation?
5
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3answers
2k views

What is the difference between an anti-virus and an IPS?

As I understand it, an intrusion protection system (IPS) detects anomalous behavior, does detection of protocol anomalies, and does signature filtering that blocks malware, DDoS, etc. An antivirus ...
5
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2answers
2k views

Port forwarding with 0.0.0.0, any threat?

I set up on our company's firewall (fortigate100d) a port forwarding to one of our Internal services. As we don't have a static public IP I used 0.0.0.0 as an external IP so the remote users can ...
5
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1answer
16k views

Websocket implication for firewalls

(I've read several questions here about websocket but apparently there's no websocket tag) If I understand correctly websockets are using TCP trafic over port 80. What are the implication, if any, ...
5
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1answer
2k views

Why ESTABLISHED,RELATED for INPUT only?

In many places and tutorials I see people add this line to their iptables: -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT And they do it only and only for "INPUT". What about OUTPUT and ...
5
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1answer
2k views

Firewall rules to block unwanted protocols on given ports

Does somebody has an idea, that what kind of iptables/pf rule must i use to achieve this?: i only want to allow these connections [on the output chain]: on port 53 output only allow udp - dns on ...
5
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3answers
8k views

Should I allow communication on public networks?

I apologize if this is a newb question. Reading this prompt, it appears that I should check Private Networks and uncheck Public Networks. However, Windows defaults to the opposite being checked. Am I ...
5
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3answers
869 views

Does blocking an IP with IP Tables protect you from a DOS (not DDOS) attack?

I am fairly new to network security, and I just learned about the Fail2Ban framework you can use for automated exploit detection/prevention. It says that you can protect yourself from DOS attacks by ...
5
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2answers
3k views

Security of Site-to-Site VPN vs Client VPN

My company provides a service to another firm and connects via VPN several times a day. The service involves accessing an intranet web-based application and copying files from one server to another ...
5
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1answer
1k views

How should I tunnel arbitrary protocol traffic over HTTPS?

I'm posting this question from a moving train! (Ok, maybe that's not so impressive.) This train has an annoying WiFi - it's low-throughput, high-latency, tends to lose packets, and blocks most kinds ...
5
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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 ...
5
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2answers
402 views

Is this a DNS attack?

The following graph shows the UDP DNS queries/sec (blue) and DNS responses/sec (red) of traffic passing a router over the preiod of 4 days. DNS query is a DNS packet with query/response flag set to 0 ...
5
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2answers
8k 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 ...
5
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2answers
1k views

What are the risks associated with relying on IPSec IP Filtering?

When using Windows IPSec for IP filtering whenever a filter is added you need to have a "mirror" rule (by checking the "Mirrored. Match packets..." tickbox). Because IPSec Filtering is not stateful, ...
5
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1answer
194 views

How to eradicate and recover a compromised network

I have a somewhat broad question related to a specific, ongoing threat that I am trying to define and defend against. Right now, I need to rebuild a secure access point for my mobile devices and ...
5
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4answers
2k views

Can websites access computers in LAN/Localhost through browser & how to block them? [duplicate]

Question 1: While browsing internet, can websites execute code through my browser that access websites or services that are hosted on Localhost or LAN? Question 2: Also, can data from intranet ...
5
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1answer
445 views

WAF logs show plaintext password and login in a POST header sent via HTTPS

Scenario I was monitoring some events from our web application firewall (WAF), Imperva SecureSphere, when a weird one appeared. Here is the client's POST request: POST some_url HTTP/1.1 Host: ...
5
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2answers
169 views

How does a firewall software intercept network communication?

I have a basic idea of what a software-based packet filter does, and I'm not sure if it's entirely accurate. Basically, a packet filter is a loadable kernel module that is inserted into the network ...
5
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3answers
17k views

Securing a network attached storage on the internet

I recently purchased a network attached storage for personal file storage and would like my family members to store files on the device from their computers as a remote backup. I'd like to secure ...
5
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0answers
850 views

Firewall in virtual machine

I'm putting my server to use as a file server and a firewall. I'm looking at KVM or Xen VM setup, where file server and firewall get their own VMs and host is just supplying the hardware (so Xen way, ...
4
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3answers
23k views

Best practice to block Dropbox usage

We have users sync their data at company with their home computer. What's the best way to block it? Block *.dropbox.com Find out all dropbox IPs and block IPs. For windows users, deploy GPO to ...
4
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5answers
441 views

Why wasn't the flame malware flagged by firewalls?

Why didn't any firewalls catch the flame malware siphoning out all of that data? I thought there was firewall software that looks for "suspicious" activity?
4
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8answers
104k views

How to block some websites in a small office?

I had a wireless connection in my office with one laptop. Now I bought two more laptops for my employees, and I give them Internet access. I want to block a few websites. My current connection is ...
4
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7answers
148k views

How to effectivily block torrents on my network?

As per the network policy, we have to block all torrent traffic from the network. To do this, I used to block all ports above 1024 on my firewall/proxy devices. But due to this, many other ...
4
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3answers
5k views

is it worth to implement a firewall on a web server you control?

I see the main reasons for a firewall on a web server to be defense in depth and extra cushion for a possible admin error of running an unnecessary daemon. I'm trying to see if I am overlooking ...
4
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4answers
3k views

Can you use two hardware firewalls? [duplicate]

There is a rule that says "don't use/install more than one firewalls on one computer " (software firewalls to be exact) which means if you have a network and it has five computers you can only install/...
4
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3answers
1k views

iptables rule to ban and redirect malicious traffic

I'm running Apache 2 and after analysing the access_log I discovered that my website is visited more than 800 times a day (today 924) from majestic.co.uk bot. The bot use this range of IP addresses: ...
4
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2answers
824 views

What is the background of the Reference Counter Overflow in Microsoft TCP/IP (MS11-083)?

How unique is this bug? Is there a more sophisticated and well-studied attempt behind? Is it accidence? The article below says "continouos stream to UDP". What stream? Just an hour stream of zeros? ...
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2answers
3k views

Blacklisting IP addresses — when should we take action?

I am responsible for securing an AWS environment and am noticing various recon attacks against the environment. We have the option of blocking the IP addresses in our firewall, but the environment is ...
4
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3answers
5k views

why blocking incoming traffic does not block chatting or VOIP

I just recently blocked all incoming traffic(all local ports and all external ips) in my windows 7 firewall and I understand that will not stop me from accessing websites as browsing needs outbound ...
4
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2answers
11k views

How can the nmap tool be used to evade a firewall/IDS?

Some techniques are used to secure the operating system against network attacks e.g.: firewalls, antivirus software, an IDS like SNORT, etc. To take advantage of the nmap tool, is it possible to ...
4
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3answers
245 views

Can firewalls get affected by the traffic they process

Does such attack exist? Forgive my wild imagination but is it possible for a hacker to pretend/try to communicate with a service on the server and when the firewall examines the traffic it get's ...
4
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3answers
545 views

The safest way to circumventing Iran's Internet censorship

We usually buy services like VPN, SOCKS, Kerio [Kerio Connect?]... to circumvent Iran's Internet censorship policy. Recently, one of the shops started selling [one of] Kerio's products, for which I do ...
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3answers
5k views

How do I configure nmap to verify my firewall is performing stateful packet inspection?

As part of a compliance audit, I need to run a routine scan that verifies that our firewalls are performing stateful packet inspection on incoming packets. I have a dedicated server outside our ...
4
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4answers
8k views

Are firewalls required if using a VPN [closed]

If you are using a VPN to transmit data from router to router, do you still need a firewall? I am using a VPN Server to encapsulate data from one cisco router to another. Do I need to have a firewall ...
4
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3answers
1k views

Servers: Why a separate device for a firewall, aside from reduction in IP spoofing or increase in performance

Why should the firewall be outside the server, excepting these two items Take the performance impact of noise off of the server. Add a physical layer between devices so they can be on separate ...
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2answers
9k views

using html5 websockets to bypass firewall TCP policy

I've read that html5 enables opening tcp sockets from the client side in its "websocket" feature. Firewalls as I recollect may be configured to block tcp connections initiated from "the outside" by ...
4
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2answers
1k views

Configure Linux to allow network activity based on binary?

On Windows, rules can be added to the firewall to allow/deny network traffic based on which binary is sending/receiving the data. Can this be done on a Linux box, and if not, why not? Is it a bad ...
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2answers
7k views

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 ...
4
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1answer
2k views

How SSH Deep Inspection works?

I just saw an option in Fortinet NGFW regarding, SSH Deep Inspection. So my question is how Deep inspection or whatever can inspect or find any malicious activity on encrypted packets?
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2answers
3k views

If nmap reports a port is open, does that ALSO mean a service is listening on the port?

I have a Thompson TG585v7 router/firewall whose firewall is configured to FORWARD several ports to a computer X54 within the LAN. These ports are in the range 1024 through to 2500 That X54 ...