Questions tagged [firewalls]

Concerned with software or hardware firewalls

Filter by
Sorted by
Tagged with
98
votes
4answers
151k views

Is it a bad idea for a firewall to block ICMP?

This question was inspired by this answer which states in part: The generic firewall manifest file finishes off by dropping everything I didn't otherwise allow (besides ICMP. Don't turn off ICMP). ...
97
votes
5answers
30k views

Someone is trying to brute-force(?) my private mail server… very… slowly… and with changing IPs

This has been going on for about 1-2 days now: heinzi@guybrush:~$ less /var/log/mail.log | grep '^Nov 27 .* postfix/submission.* warning' [...] Nov 27 03:36:16 guybrush postfix/submission/smtpd[7523]:...
85
votes
5answers
92k views

Should SSL be terminated at a load balancer?

When hosting a cluster of web application servers it’s common to have a reverse proxy (HAProxy, Nginx, F5, etc.) in between the cluster and the public internet to load balance traffic among app ...
81
votes
10answers
104k views

Why do people tell me not to use VLANs for security?

I have a network, where a have a couple of VLANS. There is a firewall between the 2 VLANs. I am using HP Procurve switches and have made sure that switch-to-switch links accept tagged frames only and ...
74
votes
5answers
35k views

What techniques do advanced firewalls use to protect againt DoS/DDoS?

It is hard to protect a server against Denial of Service attacks, DoS/DDoS. The two simple ways I can think of is to use a server with much resources (e.g. CPU and memory), and to build the server ...
72
votes
8answers
13k views

If we are behind a firewall, do we still need to patch/fix vulnerabilities?

I have recently joined a security focused community in my organisation. Many of our products are deployed in the intranet (on-premise) nothing in the public cloud. So, the internal portals can be ...
68
votes
5answers
10k views

Advised to block all traffic to/from specific IP addresses

My CFO received an email from a director at a financial institution advising that all traffic (inbound and outbound) from certain IP addresses should be blocked at the firewall. The director at the ...
61
votes
9answers
12k views

How do you explain to experts that a database server should not reside in the DMZ?

Our security experts, database administrators, network team and infrastructure team are all saying it's OK to have the database server located in the DMZ along with the HTTP server and middle-ware ...
58
votes
10answers
112k views

Why block outgoing network traffic with a firewall?

In terms of a home network, is there any reason to set up a router firewall so that all outgoing ports are blocked, and then open specific ports for things such as HTTP, HTTPS, etc. Given that every ...
43
votes
5answers
53k views

With IPv6 do we need to use NAT any more?

I'm wondering how to use NAT with IPv6. Seems that you don't even need it any more. So what exactly is the concept behind firewall configurations in IPv6 environments?
40
votes
7answers
30k views

Are two firewalls better than one?

Let's say that our first firewall has some vulnerability and a malicious person is able to exploit it. If there's a second firewall after it, he/she should be able to stop the attack, right? Also, ...
39
votes
7answers
14k views

Port Knocking is it a good idea?

Normally for a server I like to lock down SSH and other non-public service to only be accessible by certain IP addresses. However this is not always practical if the business doesn’t have static IP ...
37
votes
6answers
229k views

Difference between IDS and IPS and Firewall

The differences between an IDS and a firewall are that the latter prevents malicious traffic, whereas the IDS: Passive IDS: the IDS only reports that there was an intrusion. Active IDS: the IDS also ...
35
votes
4answers
35k 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 ...
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
7answers
97k views

How to bypass tcpwrapped with nmap scan

I'd a scan task and I faced following result Host is up (0.032s latency). Scanned at 2012-10-25 16:06:38 AST for 856s PORT STATE SERVICE VERSION 1/tcp open tcpwrapped 3/tcp open ...
28
votes
3answers
8k views

Is it practical to pre-blacklist certain GeoIP regions?

In recent events, a server I've been managing with has been under a few attacks, a risk you take when hosting a web-server. The firewall has been set up properly to only allow connections through the ...
26
votes
8answers
6k views

How to respond to a SSH brute force attack on a single VPS?

I logged onto my VPS this morning to find millions of failed login attempts for the root user and other users that don't even exist. I took the below measures to try and obfuscate the attackers ...
25
votes
12answers
64k views

Public DMZ network architecture

Years ago, when I was a student, a network security professor taught me in a class what a DMZ is. The architecture he used in his slides was similar to this one: Now that I got employed, my boss, a ...
25
votes
6answers
7k views

What is the difference between $200 and $1,000+ Firewalls?

Instead of asking about the pros and cons of specific hardware, I thought I would ask a broader question: What are the differences between really expensive and inexpensive firewalls? What extra ...
24
votes
9answers
27k views

How important is NAT as a security layer?

I've signed on to help a department move buildings and upgrade their dated infrastructure. This department has about 40 employees, 25 desktops, an old Novell server, and a handful of laboratory ...
24
votes
2answers
2k views

What does the Juniper backdoor actually allow an attacker to do?

The Juniper ScreenOS backdoor recently discovered provides administrative access to these firewalls, but in terms of access to valuable data can it actually provide an attacker with anything useful ...
24
votes
4answers
82k views

Windows Firewall - how to block inbound for all .exe files in a folder

In Windows Firewall with Advanced Settings I can create a rule which blocks all inbound or outbound traffic for particular program by pointing to its .exe file. The problem is that this program has ...
23
votes
3answers
7k views

This company is telling me that I need a firewall. Do I? [duplicate]

Do I need to buy a firewall? The website networksecure247.com is trying to sell me one. They call and say that "alerts" keep coming up on my network. I have a 2013 Dell computer, and the firewall from ...
23
votes
7answers
4k views

How can I publish data from a private network without adding a bidirectional link to another network

I was just wondering how I could build a private network where it is physically impossible to gain access from outside but still have the option to publish data to some remote server. As an example: ...
23
votes
5answers
4k views

To firewall or not to firewall?

There's recently been some discussion (to be generous) about the pros and cons of having a firewall deployed in front of servers. The con mainly being that it's a point of failure in case of a DDoS. ...
23
votes
2answers
10k views

Reject IP packets with an ICMP error, or just drop them?

Consider an internet-facing host (the outer firewall). What should be done with undesired traffic: just drop it, or send back an ICMP error such as port unreachable? (In Linux terms: iptables -P DROP ...
22
votes
5answers
5k views

Neural networks & anomaly detection

Neural networks, with their ability to learn behavioural patterns from arbitrary data, seem like a natural way to deal with intrusion detection. There are many academic papers on the topic which ...
22
votes
1answer
6k views

What is a Web Application Firewall?

What is a Web Application Firewall (WAF) and what are some of the things to look for in an effective one? Why would you deploy a WAF instead of just an IPS?
21
votes
4answers
30k views

How are spoofed packets detected?

My assumption: When a firewall is configured to drop spoofed packets, it tries to ping (not necessarily ICMP) the source IP and sees if it belongs to a real host or if it's up, and if not, it drops ...
21
votes
5answers
14k views

Do you detect/react to DNS tunnelling?

I've just seen a talk about tunnelling TCP/IP over DNS requests, because port 53 UDP is usually open and unfiltered. What techniques exist to detect and block such tunnels, and have you ever seen that ...
20
votes
6answers
39k views

What is the best practice for placing database servers in secure network topologies

I have a classic DMZ architecture: My webserver is placed in the DMZ. The webserver needs to communicate with a database server. This database server is the most critical component of my network as ...
19
votes
8answers
5k views

A destructive force can always leak information through HTTP packets. Should I bother configuring outbound rules on my firewall?

I know my way around firewalls, but I am in no way a security expert. And recently, I am wondering how to effectively configure the outbound rules of any company's firewall. For the question's sake, ...
19
votes
4answers
4k views

Detect non HTTP packets using port 80

We are currently doing port whitelisting on our firewalls which is working well but this of course does not prevent the implementation of side channels or the misuse of these ports for other purposes. ...
19
votes
2answers
336k views

What are the TCP/UDP ports used by torrent applications?

I want to block torrent traffic on my network because it is utilizing too much bandwidth and disrupted my network traffic. What port range should I use and what protocol TCP or UDP?
19
votes
4answers
3k views

ESET warns: Skype attempting to communicate with unknown remote computer

I am frequently getting warnings from my ESET firewall, like that pictured below, that Skype is attempting to communicate over SSL with a remote computer that has an untrusted certificate: The remote ...
19
votes
2answers
37k views

Wireless client isolation - how does it work, and can it be bypassed?

Many SOHO routers these days support a feature called "wireless client isolation", or similar. What this is supposed to do, in principle, is to limit the connectivity between wireless clients ...
17
votes
6answers
10k views

How does a network admin block the reverse SSH in company?

Given firewall inbound: all are blocked outbound: allow port 80, 443 Problem colleagues are still able to ssh to home device by port 80/443, and establish a reverse ssh tunnel from company to home, ...
17
votes
6answers
5k views

Does it add anything to restrict IP address?

I have an https website that is protected by a login form (username + password). Does it add anything, protection wise, if I put this website behind a firewall that only allow certain IP address?
17
votes
3answers
26k views

Proxy vs. Firewall

I understand that very simply put a proxy is a sort of 'man in the middle' allowing/denying access to certain services/resources. Strictly in terms of security (I mean here privacy, parental control ...
17
votes
2answers
18k views

Why is Windows Explorer making external connections?

McAfee is seeing Windows Explorer (explorer.exe) establishing connections to external IPs: Also verified with cmd: C:\Windows\system32>tasklist|find "explorer.exe" explorer.exe ...
17
votes
1answer
4k views

Cybersecurity “Airport model”

For the last few months, I have heard about a next generation model of Cybersecurity called the "Airport model." Does anyone have more information about it?
16
votes
4answers
39k views

Tips for a secure iptables config to defend from attacks. (client side!)

Own examples: ############### # KERNEL PARAMETER CONFIGURATION # PREVENT YOU SYSTEM FROM ANSWERING ICMP ECHO REQUESTS echo 1 > /proc/sys/net/ipv4/icmp_echo_ignore_all # DROP ICMP ECHO-REQUEST ...
16
votes
2answers
14k views

Kerberos authentication over the public internet

What are the threats to having the KDC accessible via the internet for remote clients? It's my understanding that the authentication is a challenge/response protocol and that the password is never ...
16
votes
3answers
15k views

Running windows in virtual machine, should I bother with security?

I'm running Windows in a virtual machine on my mac (via Parallels). Should I bother installing antivirus, firewall and using other conventional wisdom practices (like don't open unknown .exe etc)? I ...
16
votes
2answers
14k views

Is it not safe to open MySQL's port to the internet?

The consensus on this Server Fault question seems to be that opening port 3306 for MySQL is more dangerous than using an SSH tunnel to access MySQL. I would think that with strong credentials you ...
16
votes
3answers
6k views

Setup a private VPN for family in China?

I have family in China. During the past weeks their internet connection was severely limited. VPNs such as Astrill and similar weren't working anymore. Is it possible to setup my own VPN (or ...
15
votes
6answers
1k views

Firewall philosophy

I've always been taught/believed that with a corporate firewall, you block all outgoing traffic to start, then open up only the holes you need for specific traffic. This makes sense to me from both ...
15
votes
1answer
631 views

Should a server be considered compromised simply because a port was open?

Earlier today I received a notification of a security incident at Mandrill. At first I was concerned, but then after I dove into the details I became confused as to why they considered this noteworthy ...
14
votes
5answers
14k views

What kind of attacks against home router's NAT do exist?

I always thought NAT was some kind of a security feature and I still think it is, because if it didn't existed the internet, respectively the clients behind NATs, would be even more insecure, since ...