Denial of service attack, is an attempt through some means to make a computer or network resource unavailable.

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DDOS Mitigation Services [duplicate]

Over the past week we have been a victim of two seperate ddos attacks varying in scale. The last one was very large and very hard to mitigate. We are looking at solutions from veriSign and Akamai ...
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2answers
210 views

CentOS Server keeps grinding to a halt, then comes back up

CentOS 5.2 LAMP server The server slows down to a point where no services are responding. After a few minutes, it comes back and is running well. The server keeps doing this cycle, what could be ...
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3answers
389 views

Somebody eating all our bandwidth, what should I do?

OK, this is frustrating, my site got thousands of page views/connections in the last 3 days and finally we ran out of monthly bandwidth. We bought more bandwidth and closed the site for maintenance. ...
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1answer
1k views

Protecting against UDP flood

One of my servers is being flooded with udp packets on random ports. 12:11:54.190442 IP 182.48.38.227.60173 > localhost.51523: UDP, length 1 12:11:54.190447 IP 182.48.38.227.60173 > ...
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3answers
186 views

Apache relaying to prevent DoS

I've been wondering, is there a technology that relays (slows down) responses to a given IP according to the rate It makes requests? E.g I have an apache server with a "heavy" API service that I want ...
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2answers
132 views

In what way am I more likely to be DDoS'd? Via http or other ports? [duplicate]

I am writing a web service that has a lot of vicious competitors. Vicious as in: people have been getting DDoS'd within hours of setting up shop in this arena. The service will consist of: a ...
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2answers
793 views

Is my server being used as a proxy or is a DOS underway? Lots of traffic in my apache log

I have a slice with a hosting provider that has a basic lamp stack setup. I was checking my apache logs today and I'm getting total random (it seems) request to my apache server. For instance, here ...
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1answer
87 views

Can't figure out this attack, getting botnets and something else

About two months ago a site of mine started getting some sort of attack, and after further investigation I found it to be botnet zombies and something else which I can't figure out. My site is not ...
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2answers
145 views

defend dos attack

my website is crippled due to simple request from many ranges of ips, tens of thousands or more request per second. Is there a way to defend this kind of attack? Is there a way to trace back to the ...
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1answer
147 views

Is it normal to collapse VPS CPU with this script?

This is the script, it comes with mod_evasive: #!/usr/bin/perl #test.pl: small script to test mod_dosevasive's effectiveness use IO::Socket; use strict; for(0..100) { my($response); ...
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1answer
2k views

nginx: Prevent DoS by limiting worker processes/connections

If I limit my nginx worker processes to 1 and allow for 500 connections, what happens if I exceed this limit? Does the server return a 503 Service Unavailable? Basically, I'm trying to secure my ...
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2answers
1k views

Apache SSL Renogotiation (thc-ssl-dos)

Looking at thc-ssl-dos, it only affects SSL enabled web sites with renegotiations enabled. I have been checking a few servers and have the following questions; First; renegotiations are disabled by ...
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2answers
3k views

Kernel Printk: xx message suppressed

Hi I have a watchguard firewall, and I lost access to the firewall before xmas, therefore I visited the site, upgraded the firewall to the latest firmware but unfortunatly, I am now having similar ...
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2answers
116 views

Resolving a prolonged DDoS [duplicate]

I've been totally unable to use my server for the last couple of days. I've been contacting the owners of the IP's who are attacking me but its an uphill battle. Since I don't know who is doing the ...
2
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1answer
544 views

DoS - Apache threads hanging when not receiving TCP ACKs after sending HTTP response

In summary, I had a case where all Apache threads were hung because all of them were waiting for a TCP ACK from clients after having sent the HTTP page, and because of that, the Apache threads were ...
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1answer
338 views

Wich module to defend my apache server?

Well I find this 3 apache modules (mod_evasive, mod_qos, mod_security) but I want to know wich is better to defend my server from a Denial-of-service attack? Server version: Apache/2.2.17 (Win32) ...
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2answers
203 views

How do I locate a process on Debian Linux that is creating a large amount of network traffic? [duplicate]

Possible Duplicate: My server's been hacked EMERGENCY We have a remote Linux (Debian) server, which is, apparently, being used as a platform to commit a DoS attack. We have been warned ...
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4answers
1k views

Tomcat denial of service

The last two days our Tomcat 5.5 Linux-based webserver has been broken down within minutes by starting thousands of downloads and stopping them. Some request paths in the access log end with a ...
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1answer
378 views

Apache's built-in anti-dos mechanism by returning code 403?

In the process of learning more about how to survive simple DoS attack for my Apache server, I found some script to initiate attack on my own server and I notice that Apache returns error code 403 ...
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2answers
864 views

iptables rate-limit module problem

I am using iptables' rate-limit module to prevent DoS attack (I know it cannot stop a full scale DDoS but at least it can help with smaller attacks). In my rules I have something like: ...
2
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1answer
386 views

Where can I find DoS attack simulator [closed]

I am taking a Security module and my project team intend to study DoS attacks by simulating them to better understand the mechanism, the damage and preventing mechanism, etc... Could someone please ...
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2answers
229 views

iptables logs but doesn't drop packets

I am trying to create some simple iptables DOS protection rules for my web server. I was doing testing on the following rules: iptables -N LOGDROP > /dev/null 2> /dev/null iptables -F LOGDROP ...
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5answers
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Ec2 Denial of Service: Securing cloud based website from DOS attack

How can I prep up my website infrastructure running on an EC2 instance against DOS attacks? I run apache with nginx as reverse proxy
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695 views

Windows Server 2008 Denial of Service Detection

We have a Windows 2008 server that hosts a file share in which a SQL server database is stored and accessed from another SQL server on the same network. Periodically, the database become inaccessible ...
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2answers
848 views

DDoS Attacks on Game Servers [duplicate]

We run a fairly large game server hosting company with about 60 machines running Server 2008, and DDoS attacks something we have been dealing with for a long time. Unfortunately, due to the prices of ...
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444 views

Detecting DOS attack

On one of our systems we see many requests that take 75 seconds. Under low traffic responses are ca 0.3 seconds. What I am wondering is if someone is trying to keep connections open in order to ...
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484 views

Fail2ban advice on banning IP's and HTTP

I've recently installed fail2ban as a way of keeping one of our web servers secure from SSH attacks and HTTP attacks. At the moment I'm getting a lot of ssh attacks but fail2ban are banning and then ...
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1answer
2k views

Logging Timeout'd Request in Apache 2.X

I am migrating some applications from Apache 1.3 to 2.2. We used to run some tests where attacker opens some HTTP connection to our server, and do nothing. Apache 1.3 would log the following 408 ...
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678 views

what should be limit to use for IPTABLE rate limiting for a webserver

I see on my webserver some logs as follows 203.252.157.98 - :25:02 "GET //phpmyadmin/ HTTP/1.1" 404 393 "-" "Made by ZmEu @ WhiteHat Team - www.whitehat.ro" 203.252.157.98 - :25:03 "GET ...
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2answers
5k views

HTTP server, SYN flooding, and DoS attack questions

I am making an http server in c. It is in a pre-alpha stage but seemed to be stable enough to deploy on my server and run 4 minimal websites. It has been running seamlessly for two days until this ...
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4answers
706 views

Preventing Denial of Service Attacks

What's the most effecient way to prevent DoS attacks for game servers? Currently I do something like this: iptables -A INPUT -p udp --dport 27015 -m length --length 28 -j DROP Is it the best way?
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559 views

Ping size limit - FreeBSD

In the man page for FreeBSD ping: -s packetsize Specify the number of data bytes to be sent. The default is 56, which translates into 64 ICMP data bytes when combined with the 8 ...
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1answer
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How can I recognize flooding? [closed]

how can I discover if my server is performing some illegal actions, like flooding?
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2answers
284 views

Is it possible to distinguish from “good” http requests and DoS attacks?

How could I know that a lot of requests in a short period of time come from a DoS attack and not from normal browser requests?
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2answers
129 views

Has anyone experienced unintentional traffic overload due to clients' use of wget?

I am wondering if it is wise to indiscriminately block wget on servers that I maintain. Has anyone experienced unintentional traffic overload due to clients' use of wget?
3
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1answer
901 views

SYN flooding still a threat to servers?

Well recently I've been reading about different Denial of Service methods. One method that kind of stuck out was SYN flooding. I'm a member of some not-so-nice forums, and someone was selling a python ...
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3answers
605 views

Is SYN flooding still a threat?

Well recently I've been reading about different Denial of Service methods. One method that kind of stuck out was SYN flooding. I'm a member of some not-so-nice forums, and someone was selling a python ...
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6answers
571 views

Securing against DDoS [duplicate]

My client would like to have his eCommerce (custom-made) site secured from DDoS attacks. What strategies can I implement? There are multiple forms in the purchasing flow --- searching, drilling-down ...
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8answers
422 views

Servers harrassed by individual on constantly changing IPs

We run a community product. There is an individual (a little PoS kid) in the UK that is harassing our site for the last 6 months. His daily task is to create a new account, post a bunch of illegal / ...
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2answers
1k views

Best way to use large IP blacklist to deny access to a Windows 2008 web server?

Basically, I'm looking for a solution similar to the ones mentioned in a similar (but Linux-focussed thread) located here so that I can deny access to blacklisted IPs. I am specifically focussed on ...
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398 views

Finding Evidence of a Denial of Service Attack (Linux)

We had a Gentoo Linux server (that was updated weekly or bi weekly) that higher ups claimed did a denial of service attack on the whole local network and brought it down. Are there any log files we ...
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1answer
279 views

Repetitive / incessant hits to pages, blank referrer, non-malicious

I asked this question last week, and followed the debugging advice and now have additional information. I have an odd problem-- on a high traffic website (millions of visitors a month), every day we ...
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3answers
445 views

How to stop repetitive hits from same host to same URL?

I have an odd problem-- on a high traffic website (millions of visitors a month), every day we get about 20 or so situations where one host begins incessantly requesting the same page, over and over-- ...
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5answers
2k views

MSSQL 2005 on port 1433 gets DOS from infected servers

I have a SQL Server 2005 server hosted outside my firewall at a data center. It is fully up-to-date on patches, etc. There's some old MSSQL worm (Slammer?) that STILL infects thousands of servers ...
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2answers
3k views

(D)DOS - tcpdump established connections analysis (too many established connections)

¿How can I debug this problem? (I've got full tcpdump captures) I have a TCP server into which many clients establish persistent connections. Normally all these clients behave, and I never reach ...
2
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5answers
619 views

DDoS attacks [duplicate]

How to prevent DDoS attacks on Windows/IIS servers ?
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4answers
203 views

AD Domain Controllers being Slammed

My Windows Server 2008 Domain Controllers are getting hundreds of log in attempts per minute. For the most part the IP addresses are not in the Event Log however the ones that do occasionally show up ...
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510 views

Do reports of packet flooding suggest a DOS attacK?

Our E1 connection is being closed by our firewall*. It happens intermittently every few days. I find log entries like this one around the same time as the dropout: Jun 2 09:53:35 sg580 kernel: ...
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3answers
164 views

What criteria do you use to determine if someone is hammering your server?

When you go through your logs, what criteria do you use to determine if it's you (ie: you need to beef up your server/s) or them (ie: they're verging on a DoS)? How many connections/second would you ...
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875 views

Is account lockout a denial of service attack waiting to happen?

The default behaviour of windows is to lockout an account after a number of failed authentication attempts (usually three).. This means that with the following net use \\targetmachine\c$ ...