Questions tagged [denial-of-service]
A denial-of-service (DoS) attack is an attempt to deny service to legitimate users by sending extreme amounts of requests to a server.
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Will iptables INPUT chain apply to packets forwarded through OpenVPN?
I have forwarded some ports from an internet facing machine to my home server using the NAT table and PREROUTING chain in iptables. The NAT destination IP is on my OpenVPN VPN.
I want to protect ...
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29 views
I disallowed use of proxy capability on Ubuntu Apache 2 web server. How can I check it?
A few weeks ago I put up a web server that runs as as virtual host handled by Apache 2 on my Ubuntu box. I started having a problem where the web site would get sluggish. Then soon after that it got ...
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52 views
How to allow only 100 half open SYN connections
I'm running Ubuntu and want to allow only 100 waiting SYN connections at a given time,
and drop the rest.
How can I configure iptables to implement this rule?
Or sysctl config to allow only 100, and ...
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45 views
High CPU load on SYN flood
When being under SYN flood attack, my CPU reach to 100% in no time by the kernel proccess named ksoftirqd,
I tried so many mitigations but none solve the problem.
This is my sysctl configurations ...
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1answer
195 views
Increased traffic - Server probed by bots?
Since December 24 my server experiences increased resource consumption. Additionally the Nginx server seems to be unstable which causes several errors.
The CPU usage used to average at around 5%. But ...
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1answer
86 views
Using wget to download from site with DDos protection
When trying to load pages with wget I have the following error:
$ wget --user-agent="Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1)" "https://www.cruisersforum.com/forums/&...
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122 views
Reverse Proxy UDP from VPS to Dedicated Box?
I'm quite new when it comes to network administration so I've got some questions that I'm seeking answers for...
I have rented a Dedicated Server from hetzner.com in order to host 2 game servers and a ...
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21 views
DNS Server is flooded with localhost resolution
I have a public DNS server and can be accessible by anyone. Recently we have been flooded with thousands of DNS queries trying to resolve a "localhost" such as these:
Is this supposed to be intended ...
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1answer
72 views
Send packet to a machine behind router
Context
I'm learning how the internet works, and I am trying to send a TCP packet from my VPS to my computer.
My VPS has a specific public IP address so I can easily send from my computer to my VPS. ...
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2answers
2k views
limit max UDP bandwidth per IP using iptables?
'm using a VPS to host a VPN for DDoS protection, but I've been wanting to find a way to rate-limit UDP traffic per IP to prevent UDP floods. I'm looking for something to only allow X MBPS of traffic ...
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1answer
298 views
Blocking DNS amplification attacks on ipv6 with iptables
I'm running a small Pi-Hole DNS server on my VPS, and I have the following iptables rules enabled to stop the DNS ANY amplification attack:
*raw
-A PREROUTING -p udp --dport 53 -m string --from 40 --...
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1answer
154 views
Cloudflare 525 error code and port scan
Today, Cloudflare return code 525 for some https connections.
And I see many connections in iftop on the origin server. This connections - port scan.
I used iptables, and block all packets, not from ...
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1answer
37 views
This IP was already used for a trial - spaming admin email
I use amazon lightsail and I get a lot of generated emails saying:
"The IP .... was already used for a trial license on 2019-03-13"
Where the IP changes to different IPs. The emails are from my cron ...
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0answers
24 views
Turning off network during Incoming DDOS
Sometimes on a server of mine, there is unsolicited incoming traffic (mix of random ports & random protocols beyond tcp/udp/icmp also) which starts peaking at 1 to 2 GBit/s while the outgoing ...
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95 views
How to block fake IP adresses?
on my webserver I find in the apache-logfiles:
[Wed Jan 09 16:29:10.660069 2019] [:error] [pid 11705] [client 66.249.66.66:39066] script '/var/www/fairtragen/7327991037366506690.php' not found or ...
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1answer
643 views
Block requests in lighttpd made with HTTP/1.0 and only allow HTTP/1.1
I have a lighttpd web server that delivers PHP-generated webpages. This server is currently facing a lot of traffic due to a DDoS bot attack, and I am looking for a way to block or mitigate some of ...
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2answers
2k views
What happens to your connection / modem when you are DDoSed and how can you prevent it? [closed]
I want to learn more about how DDoS and DoS attacks affect the network and how you can prevent them. I know how they 'work' and why the network is overloaded but I still dont know if a router / ...
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1answer
56 views
Being ddos-ed or my VPS has been compromised?
VPS bandwidth was suspended due to over usage.
Didn't really promote my website at all cus it is still under development.
Installed IFTOP and below is what I have captured.
Any advice is greatly ...
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60 views
One machine on network switch seems to be killing network for others - Hacked?
I have been trying to setup a new headless Ubuntu server and I have been having all sorts of issues with crashes and server no longer being available. I initially thought that these were hardware ...
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2answers
64 views
Checking if a router is online or offline?
Recently I've been receiving ddos attacks to my router, for educational purposes, I want to know how the attacker is finding out when my router has been ddosed.
They said they are doing something to ...
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0answers
56 views
Data security in server at home
I am a beginner linux user, and am planning on provisionally opening a game server on a machine I have at home. In addition to the possible DDoS attacks that may occur on this server (the server will ...
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1answer
778 views
Make Game Server DDoS-Protected
I'm a real noob in "server discussions".
Im running game servers on Debian 8 but the datacenter doesn't provide physical firewall, So Im looking for a way to make my servers ddos protected, I did ...
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1answer
43 views
How to generate normal web traffic for DDoS Testbed to compute the false positive rate?
I'm implementing an algorithm to detect HTTP GET Flooding Attacks. I have used Bonesi as a bonet traffic generator to launch attack traffic. However, I need a real trace of a normal web traffic (or ...
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1answer
2k views
TP-Link DoS protection blocks Bonjour
We have an Apple-centric office and as such we rely on Bonjour (mDNS) for auto-discovery of things like printers, AirPlay targets, and pseudo-servers (e.g. exchanging files between desktop computers).
...
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55 views
Having too many ADPM and ICMP log in router admin panel
Recently, I feel that the speed of network became too slow. And I open router admin panel and have a look at the log messages. I found that there are many messages contains word "ADPM" and "ICMP", I ...
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1answer
232 views
Designing a custom small DDoS detection and defense sytem [closed]
Am very new to the topic so I would like some guidance where to get started.
What I want is, some tools to programmatically observe network traffic and preform some actions on the traffic. I don't ...
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2answers
5k views
Trying to understand anti TCP SYN flood attack IPTables rule
I’m currenlty working on a university assignment. I’m learning about firewalls and I need to configure IPTables on a Ubuntu machine to prevent a TCP SYN flood attack.
I understand that this type of ...
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1answer
6k views
What happens if the router is ddosed?
I don't know what happens if a router gets DDOS'ed? Does it brick it self or it just disables its ip? And if the ip disables its just easy fix by power cycling the router to get a new ip and getting ...
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1answer
71 views
Is there a way i can protect myself from DDOS attacks?
I got my IP spoofed somehow and how? Its because i visited a site which has a ip grabber and then a redirect to the site and my router is ADB and it has firewall but i don't think it won't help so i ...
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1answer
506 views
Am I under a DDoS attack?
OK, so here's some info:
Fedora23 running in VirtualBox on a Windows 7 Host.
Public-facing router has no DMZ, but port forwarding from 2325 (external) to 1194 (internal) and the internal static IP.
...
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1answer
4k views
Does Transmission Bittorrent client use UDP?
I am running a Transmission Bittorent server to upload various Linux ISOs.
I am currently being flooded by UDP packets. I mean the DoS protection in the Archer C5 home router and it blocks parts of ...
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1answer
3k views
I can access websites through the web browser, but I can not ping them or interact in various other ways
as of around two weeks ago I've been having really weird interactions with the Internet that I can't explain, but please keep reading. I've tried looking for the issue myself and haven't found ...
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1answer
61 views
How can I bridge my router to my Linux OS?
I am getting ddosed a bit so I want to send all my router traffic to my Linux OS as a somewhat mitigation. How to send my router traffic to my machine?
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1answer
989 views
Implementing fail2ban the correct way
I have a Django web app where people write comments and upvote/downvote others' comments. The webserver is gunicorn + nginx (reverse proxy). The db is postgresql. The db and web app reside in two ...
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1answer
2k views
Invalid URI in request and apache stopps working
Today our apache stopped working, he did not crash but stopped to response.
The only error i can see in the error_log is this:
[Thu Feb 11 10:00:05.245233 2016] [core:error] [pid 7496] [client 169....
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2answers
2k views
How virtual machines will be effected from DDoS attack on same physical server?
I mean let's suppose that there is a large DDoS attack to a virtual machine which is running on a physical server with other 10 virtual machines, how the other virtual machines will be effected from ...
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1answer
138 views
Firefox 43: Uploading to Youtube results in DoS behaviour
I've been trying to upload a video to my channel today, only to notice that Firefox starts using 100% CPU time on a single core and then suddenly, I and everyone in my household can't connect to the ...
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1answer
734 views
DOS attacks using cmd and protection against them
After finding someones ip you can easily send pings to them to make DOS attacks. Me and my friend tried to make a defense against them and wanted to know how a low level attacker can send this DOS ...
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2answers
68 views
Questions Regarding DoS
I have a few questions i still haven`t been able to get an answer to.
If someone DoS you, do it affect all computers connected to the router or just the computer that is being attacked? For example: ...
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1answer
209 views
Webserver accessible only from CloudFlare?
I wan't to avoid getting DDoSed as much as possible i can, so i thought if it's possible to set my web server to communicate only through CloudFlare. Any request from another source will be rejected, ...
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3answers
17k views
How ping a server which has ICMP blocked
I'm trying to ping a server which has ICMP blocked with normal ping. It's showing:
Request timed out
Is there any other method to ping it?
9
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1answer
5k views
What is a safe ping frequency without it being considered a DDoS attack?
I am trying to chart the uptime of a server by regularly pinging it and Google and then comparing the ping times. I want to keep doing this over a period of—let’s say—a week.
I am sending a set of 5 ...
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1answer
2k views
My home IP (supposedly) was involved in a DDoS attack
There did not seem to be any SO community dedicated to computer security, so I'll ask here...
As the title implies, my home IP (supposedly) was involved in a DDoS attack.
I got a phone call from a ...
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2answers
202 views
Is it possible that I have caused a DoS to my son's tablets
I have three Internet connections at home, they are not connected to each other in any possible way, they are from three different ISPs
FTTC #1 , the white modem and the black and white router
FTTC #...
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3answers
2k views
Will the maximum speed of a network card reduce the impact of an incoming DDoS attack?
I’m wondering if the maximum speed of a network card would reduce the chances of a DDoS affecting a home-hosted website.
In this scenario, I’m hosting my website from an Android Tablet where the ...
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1answer
145 views
DDoS/botnet or what's going on, cloudflare.com?
This is small output from tcpdump -i re1 'port 25':
14:00:10.732034 IP cf-190-93-254-113.cloudflare.com.http > MY_IP.smtp: S 4234708404:4234708404(0) win 8192 <mss 1412,nop,wscale 8,nop,nop,...
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1answer
2k views
DDOS on port 443?
Recently my friend asked me whether his network is secure because he is setting up a game server on port XXX.
I opened up Nmap on my linux machine and found port 443 opened. I tried to access
https:...
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0answers
392 views
Configure Router for better DDoS protection Actiontec MI424WR
So for the past month, my server has been attacked by script-kiddies three times. The server is mainly used as a minecraft server. I am getting worried that this is becoming an outbreak as many of ...
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32 views
How can I efficiently filter Dos packets? [duplicate]
I have recently been the victim of some Dos attacks.
The facts : I received a very high amount of packets saturating my connection and preventing me from accessing the Internet during one hour (...
0
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1answer
511 views
Compromised Debian server sending DDOS attack
I have a server online that apparently has been compromised and it sends DDOS attacks to another ip. The system is a debian 7 server, hosting a few wordpress, joomla websites, and airtime to host a ...
