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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Lots of failed authentication requests from all over the world on brand new GGL cloud SFTP server

I created my first public server - an SFTP server hosted on google cloud. I was checking the auth log during the 2nd day of testing and noticed that I'm getting 4-10 hits from random people every ...
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Ping-attack on a server?

Ok, following might be a stupid question but since I'm really new to hacking and cyber security stuff and I'm just thinking about how an attack on a website might look like, I'm gonna ask this: What ...
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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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3 votes
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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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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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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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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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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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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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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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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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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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Simple ICMP DoS attack example with cmd on Windows 10 crashing the attacker's computer?

I had to make a simple batch file as an assignment in which I had to attack another PC on the same network by a ICMP DoS attack and analyze the traffic using Wire-Shark. Here the code which I used: ...
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3 votes
1 answer
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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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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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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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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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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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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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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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9 votes
3 answers
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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?
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9 votes
1 answer
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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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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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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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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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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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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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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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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 (...
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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 ...
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