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Questions tagged [iptables]

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An application that allows a user to configure the tables provided by the Linux firewall. iptables is succeeded by nftables as of 2014.

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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 ...
20
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2answers
1k views

Fully transparent proxy

By default, mitmproxy will use its own local IP address for its server-side connections. What I want instead is mitmproxy to use the client’s IP address for server-side connections. The following ...
16
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4answers
40k 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 ...
12
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1answer
24k views

Is it safe to disable connection tracking in iptables?

While reading about NOTRACK target of raw table in iptables, I encountered an article suggesting that for certain traffic you could (or even should) disable connection tracking. The two examples were: ...
11
votes
1answer
3k views

Has a remote rogue DNS client managed to slip through the first iptables rule of a Linux DNS server?

Ubuntu 20.04 iptables 1.8.4-1 I experienced a situation where a remote system seemed to be able to slip through the first iptables rule of a Linux server located behind a NAT router: -A INPUT -s <...
9
votes
1answer
8k 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
2answers
24k views

Test firewall rules (Linux)

I have a question about how to test the firewall rules. To be more specific, for academic purpose I have to set up a machine which will accept all kind of packets o a specific interface. I added an ...
8
votes
1answer
3k 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 ...
7
votes
4answers
2k views

SIP UDP request breaking through iptables

I have been investigating a few instances recently where SIP UDP traffic has been somehow evading the ruleset defined in iptables leading me to suspect that there is a hole in our rules so i'm looking ...
6
votes
5answers
2k views

Firewall demo - iptables

I have to make a demonstration about firewalls in my class as a student(university). It should be implemented using iptables on Linux. I am reading all the theories around them but I can't figure out ...
6
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2answers
5k views

How web application firewalls protect application from DDoS attacks?

How to protect a web application from DDoS by the implementation of Web Application firewalls? How effective is this method?
6
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1answer
223 views

System-Level Network Security (Packet Classification and etc.) - SELinux and Libnftnl

I read that Libnftnl is a userspace library providing a low-level netlink programming interface to the in-kernel nf_tables subsystem and it uses NFTables. Since it's a kernel related topic, at the ...
5
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1answer
2k views

ARP spoofing with Scapy. How does Scapy reroute traffic?

Background: I understand that in order to ARP spoof a victim in a network using Scapy, we need to send ARP reply packets to the victim and the gateway router with the correct destination and Source ...
5
votes
2answers
4k views

What are the security implications of net.ipv4.conf.eth0.route_localnet=1 / route_localnet?

sudo sysctl -w net.ipv4.conf.eth0.route_localnet=1 What are the security implications of route_localnet?
5
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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
997 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
votes
1answer
649 views

SSL MITM on the WAN side of my router

Hi I would like to try to sniff a typical CWMP conversation that my router does to his Auto Configuration Server (see TR-069 crash course: https://www.iol.unh.edu/sites/default/files/knowledgebase/...
5
votes
1answer
1k views

How to prevent ARP poisoning with hostapd and iptables?

I have a raspberry pi and hostapd and iptables are running on my pi. However iptables cannot block the wifi clients from communicating with each other, thus I cannot prevent them from sending out ARP ...
4
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5answers
3k views

How can I block bots that consistently hit the same URLs?

I am getting slammed hard by bots, and I am not sure how to stop them without blocking my legitimate traffic. I created some iptables rules that say, if X connections in X seconds, block, but that ...
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
votes
2answers
8k views

Benefits of REJECT over DROP on a single PC

Recently I learned about the difference between DROP and REJECT in a firewall. I understand that REJECT is better because it closes the connection immediately instead of waiting for timeout as DROP ...
4
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2answers
1k views

Executing arbitrary commands through iptables-restore input

During a pentest I found a way to add arbitrary iptables firewall rules to a server. These rules get applied by way of the iptables-restore command, and I've been wondering whether there is any way to ...
4
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1answer
523 views

SSL Strip on Fedora24

I want to perform a MITM attack on my own network, and followed several tutorials on how to use sslstrip, iptables and arpspoof. But every time I perform the attack, I lose the connection on the ...
4
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4answers
1k views

Find out what Linux software is trying to phone home

I have seen some suspicious outbound communications blocked on my VPS, which hosts a small experimental Web site, and want to find out which application is making the attempt. The server is running ...
3
votes
3answers
956 views

Make OSSEC ban ip on remote firewall

I am deploying OSSEC architecture agent-server mode. I want the server to ban ip not only on agent but also on a remote firewall (dedicated iptables server). I've seached on the OSSEC's ...
3
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2answers
3k views

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 DST=192.168.1....
3
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1answer
525 views

What are the requirements to sniff UDP packets in a Wireless Ad-Hoc network?

In a wireless Ad-Hoc network, I have two computers which communicates in UDP together from 192.168.1.3 to 192.168.1.5 I have a third computer (192.168.1.6) which wants to listen to the packets which ...
3
votes
2answers
1k views

Firewall egress filtering / quick whitelisting

Suppose your Aunt or Uncle is easily fooled by phishing attempts and their computer has multiple root kits and key loggers running. Assume their computing habits will never change. Looking at his ...
3
votes
1answer
255 views

Blocking all incoming traffic, will it still accept a response from a request I initiated?

I am a 'newbie' when it comes to firewalls, but I am trying to launch some machines that will connect to Facebook's Graphs API. I only want these machines to contact Facebook and nothing else. By this ...
3
votes
2answers
6k views

How to configure iptables for must open ports?

On my machine there are web services which can be accessed from any PC connected to the same network segment (WiFi for example). I want to use IPtables on the machine to prevent any web services from ...
3
votes
2answers
340 views

Can ipopts be used to circumvent a pf or iptables firewall source IP based blocking?

Can one use ipopts, and in particular IP source routing, to circumvent source-based blocking in pf or iptables? For example, with OpenBSD's pf: block in all # default deny block out all pass in on ...
3
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2answers
1k 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
votes
1answer
174 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 MAC=xx:...
3
votes
1answer
2k views

ufw, system-config-firewall-tui, or firewalld vs iptables

Is there any advantage (other than usability) to using ufw, system-config-firewall-tui, or firewalld rather than just using iptables? My understanding is that these other programs just simplify ...
3
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1answer
2k views

Setting up a fake AP - problem with iptables and DNS server

Im trying to set up a fake AP using aircrack-ng suite, DHCP server & iptables. After creating the fake AP: airmon-ng start wlan1 airbase-ng -c 11 -e "freewifi" wlan1mon running iptables ...
3
votes
2answers
853 views

Dedicated OS vs Debian for SOHO Firewall? [closed]

I want to set up a firewall for a small office. I have a server on which I can install an OS of my choice. I was thinking of trying pfSense but ran into some testing problems and tried IPFIre (Linux ...
3
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1answer
3k views

IPtables Linux Firewall and IPsec traffic

Can iptables filter out incoming datagrams that are IPSec-tunneled packets going to port 25?
3
votes
1answer
120 views

Which IPTables chains should I log from a security perspective

So far I've always been logging the INPUT and OUTPUT chains because I only used iptables as host firewall. Now I'm configuring network firewall which uses iptables, but I don't know whether I should ...
3
votes
1answer
3k views

Networking in Qubes OS [closed]

I've started recently to use Qubes OS and I want to set up a virtual IDS and IPS in separate VMs, but I can't figure out how the communications between different VMs works here. Each VM should be ...
3
votes
1answer
840 views

How to prevent ICMP redirection produced by a man-in-the-middle

How can I prevent my route to be redirected with redirecting ICMP packets from a man-in-the-middle? I am specifically looking to avoid someone using ettercap with the -M icmp option. From man ...
3
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0answers
167 views

Experimenting with SSLStrip+ on the same machine

I am trying to play around to understand how SSLStrip+ works by: $ cat /proc/sys/net/ipv4/ip_forward 1 $ sudo iptables --flush $ sudo iptables --flush -t nat $ sudo iptables -t nat -A PREROUTING -p ...
2
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2answers
2k views

Why can't iptables drop arp requests

I was trying to hide my laptop from my phone's network scan app. The app is using arp requests to find devices on the network. I tried everything on iptables. It doesn't work, even if i set all the ...
2
votes
2answers
6k views

IPTables default security rules for a gateway/router?

On a router such as dd-wrt or tomato, what would be some default iptables rules? I am asking for rules on a router/gateway - For example; blocking SYN flood attacks, or XMAS attacks. The basic ...
2
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2answers
438 views

Are there “LAN IPs” on the internet?

I have a home-made web application and thought that an easy way to secure it's administration interface would be to simply reject all IPs that arent from 192.168... Is this viable? is it possible for ...
2
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3answers
2k views

iptables: plaintext password protection

I'd like to find a way to block or restrict my access to the web-pages where my password is sent as a plaintext on the internet. Let's assume if I have the same password for all web-pages, is it ...
2
votes
2answers
127 views

How are my iptables rules circumvented?

I'm using ufw on a debian server and apparently an attacker is able to circumvent the filtering rules. ufw uses iptables. The server host http and mail services, and has an ssh port. I use a non-...
2
votes
2answers
4k views

MAC filtering the internet traffic?

I was trying to build a firewall where in the access to my LAN from internet should be allowed only if it matches the predefined MAC address of the device i.e,. MAC filtering, but later i found out ...
2
votes
2answers
1k views

Limit Packets Per Second

Since last week I have been seeing something fishy and it seems to be worsening. I tried many firewalls and they seem to be useless. I blocked all unwanted ports and only few ports are open so I found ...
2
votes
1answer
530 views

Port Knocking using only Iptables/netfilter

I am using the following iptables rules for port knocking. Everything works well, but it open the port for just a second and then close it. So how to improve this script to accept connection for a 30 ...
2
votes
4answers
5k views

Logging server compromised (IptabLes and IptabLex)

I am trying to figure out how it was compromised. They installed IptabLes and IptabLex in /boot. They also added /etc/init.d/IptabLes and /etc/init.d/IptabLex which simply call the respective /boot ...

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