Questions tagged [denial-of-service]

Denial of Service (DoS) is a family of attacks that attempt to force a target to use up resources (CPU time, memory, bandwidth etc) by flooding a target with useless packets, connections or tasks.

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Can someone take down Wi-Fi signal?

Is it possible that someone made an attack (DoS or something else) to my Wi-Fi router (without knowing of the password) and make my router's signal unavailable? 1) How it can be done? 2) What are ...
T.Todua's user avatar
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96 votes
6 answers
21k views

Is it safe to let a user type a regex as a search input?

I was in a mall a few days ago and I searched for a shop on an indication panel. Out of curiosity, I tried a search with (.+) and was a bit surprised to get the list of all the shops in the mall. I'...
Xavier59's user avatar
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70 votes
2 answers
22k views

How can ISPs handle DDoS attacks?

How can an ISP with low bandwidth like 50 Gbps handle a DDoS attack with more than this? I know there is a solution called "Black Hole". Is this enough to mitigate DDoS attacks or are there any other ...
R1W's user avatar
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63 votes
9 answers
11k views

Can attackers get anything with DoS attacks except crashing the service?

A DoS (short for "denial of service") attack is a form of attack used on web services which aims to "crash" the service. Is there any motive of this form of attack besides crashing the service / ...
Martin Thoma's user avatar
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61 votes
4 answers
12k views

I think I accidentally DoS'd a website. What should I do?

I was browsing a website, and stumbled across a sample scheme for password-protecting web pages. The owner of the website specifically had a page that invited people to attempt to hack it. I wanted ...
Michael0x2a's user avatar
58 votes
7 answers
12k views

Does it make sense to consider a triggerable server software crash a DOS attack?

I've found a little vulnerability in a web application running on Node.js server. It works by sending some crafted payload to the application server, which makes the application server code to throw ...
Matías's user avatar
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57 votes
11 answers
16k views

Can a DDoS attack yield any information?

Can a DDoS attack reveal any information or be used to mount a hack? My understanding is that the whole point of DDoS or DoS is to consume all of the resources/overload the server causing it to crash. ...
KosugiNinja's user avatar
45 votes
3 answers
41k views

Can I trust the source IP of an HTTP request?

As far as I've understood, if you try to issue a HTTP request with a spoofed IP address, then the TCP handshake fails, so it's not possible to complete the HTTP request, because the SYN/ACK from the ...
KajMagnus's user avatar
  • 707
36 votes
6 answers
30k views

Preventing artificial latency or "Lag Hacking" in multiplayer games

There is an attack that some people have dubbed "lag hacking", and its gaining popularity in multiplayer games. There are at-least two ways of creating artificial latency. One method of introducing ...
rook's user avatar
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34 votes
3 answers
5k views

Is there a security reason for a site to limit the number of times a user can change their password?

Is there a security reason to disallow a user to change their password as frequently as they want? I have found this security policy in a site and I am not sure why it is enforcing it. One reason I ...
kinunt's user avatar
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33 votes
3 answers
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How do DoS/DDoS work?

In the last days one could frequently read about attacks from anonymous and LulzSec against different platforms like Sony or HBGary etc. Yesterday for example they DDoS'ed soca.gov.uk and jhw.gov.cn. ...
binfalse's user avatar
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32 votes
4 answers
17k views

Normal usage vs. denial-of-service? How many requests are needed to talk about a denial of service?

Recently I used a tool to download a website and as part of the tool one could adjust the number of parallel connections. So now I found myself asking: starting from how many requests a provider could ...
Lonzak's user avatar
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30 votes
1 answer
60k views

TCP Peer unexpectedly shrunk window messages in dmesg log

We get quite few messages like these in our dmesg log on various servers: TCP: Peer 0000:0000:0000:0000:0000:ffff:d431:5861:56369/80 unexpectedly shrunk window 2522304441:2522312601 (repaired) TCP: ...
nelaaro's user avatar
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26 votes
5 answers
4k views

Is unauthorised deletion an integrity or availability issue?

During a web application test I have discovered a parameter tampering issue that allows a user to delete comments left by other users. They can't modify the content of other users' comments, and they ...
paj28's user avatar
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26 votes
4 answers
106k views

nf_conntrack: table full, dropping packet

I see a lot of these messages in /var/log/messages of my Linux server kernel: nf_conntrack: table full, dropping packet. kernel: __ratelimit: 15812 callbacks suppresse while my server is under DoS ...
hnn's user avatar
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24 votes
4 answers
11k views

Protection against account lockout DoS

Any ideas on how to protect against the following scenario? Company x uses active directory for authentication of it's employees. The company has multiple authentication points that are semi-public ...
Josh Brower's user avatar
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23 votes
4 answers
14k views

Why does a (D)DoS attack slow down the CPU and crash a server?

So I get the basic idea of (D)DoS used for flooding, but I don't quite understand how this causes servers to crash or get them to slow down due to CPU overuse. As far as I know, the thing that is ...
DrDoom's user avatar
  • 455
23 votes
3 answers
3k views

Should you care about DoS attacks if your server is using bcrypt?

(I just asked this question on "cryptography SE" and was suggested to ask it here instead) EDIT I just realized my question is mostly a dupe of: Prevent denial of service attacks against slow hashing ...
Cedric Martin's user avatar
22 votes
3 answers
4k views

New denial-of-service vulnerability in TLS protocol, based on shooting down other users' sessions?

I think I have a new denial-of-service attack on TLS, and I'd like you to check whether this is a real vulnerability. I recently learned about the proper way to drop an authenticated client session (...
Trueblacker's user avatar
20 votes
5 answers
10k views

DoS in local network computer

I'm using Snort to study detection, and I wanted to simulate a DoS attack from the inside to another computer in my home network, but I have a question. If I start to flood the target computer with ...
pedromendessk's user avatar
20 votes
3 answers
45k views

How can I block an IP, if I'm getting many http requests in a second?

If some one tried force burst attack on my website, how can I block them? Ideally, I want to block an IP if I have many http/Apache requests in a second.
lee peat's user avatar
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19 votes
5 answers
5k views

How can a DoS attack be used as part of the 'Gaining Access' phase of a hack?

I'm doing some revision for an exam and I've made a note to look at how DoS attacks can be used to gain access to a system. I can't find anything online but I found a reference to the fact here. I ...
user avatar
19 votes
4 answers
909 views

Global Blackout is a myth?

In order to shut the Internet down, anonymous claimed that putting-down the 13 root DNS servers of the Internet and therefore disabling the HTTP Internet, the most widely used function of the Web, ...
Tawfik Khalifeh's user avatar
19 votes
7 answers
6k views

Prevent denial of service attacks against slow hashing functions?

I've been thinking about bcrypt recently, and what I wonder is if there's a way to deal with the inherent (D)DoS problems with slow hashing functions. Namely, if I set up bcrypt so my machine takes ...
Brendan Long's user avatar
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18 votes
5 answers
6k views

Cloud-based DDoS as a Service

With the consolidation of cloud computing and virtualization, a really simple doubt comes to my mind: why isn't DDoS being largely offered as a service? Why don't we see cloud-based DDoS attacks? ...
Gabriel Rebello's user avatar
17 votes
5 answers
20k views

What is the difference between login throttling and temporary account lockout?

I am currently working on the redesign of a login page. I have initially suggested that login be throttled whereby pauses (incremental - in number of seconds) are introduced between each failed login ...
Okavango's user avatar
  • 415
17 votes
5 answers
29k views

How To Protect Tomcat 7 Against Slowloris Attack

I'm using Apache Tomcat 7 to run my webapp on Linux. I scanned it by Acunetix and it's telling me that my webapp is vulnerable to "Slow HTTP Denial of Service Attack". How can I protect it? Acunetix ...
Amin Sh's user avatar
  • 273
17 votes
4 answers
17k views

Best way to report a foreigner attacker's ip to authorities?

I have been under attack last week and I was able to trace down the attacker and get his IP address. The attacker was located in Germany but I live out of Europe? From your experience what is the ...
HEX's user avatar
  • 521
16 votes
8 answers
17k views

How does CAPTCHA mitigate DDoS attacks?

This seems like an easy question, but I've failed to find an answer. One of the uses of CAPTCHA is to cope mitigate Denial of Service attacks. Suppose an adversary performs excessive login attempts, ...
overrider's user avatar
  • 263
16 votes
6 answers
10k views

What is a DoS Attack and how does it differ from a DDoS attack?

Can someone explain to me the concept of DoS attacks for web applications? Also, what is the distinction between DoS and Distributed DoS (i.e. DDoS) attacks? Wikipedia says: In computing, a denial-...
Geek's user avatar
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16 votes
8 answers
3k views

Bruteforce vs Denial of Service

I had a problem presented today which I found quite interesting. You have an application with a management panel. You know some of the accounts as they are standard. You want two things: You want ...
Lucas Kauffman's user avatar
15 votes
4 answers
5k views

How to deal with this denial of service attack on an Apache server?

I was the target of different attacks today. The last one created this traffic on port 80. Apache is down and the load on server remains high. Firewall is enabled. Any suggestions? 15:27:10.203993 ...
antony's user avatar
  • 309
15 votes
6 answers
77k views

Google: "Unusual traffic from your computer network"

I often happen to receive the message: "Unusual traffic from your computer network" while googling in Russian speaking countries. Google explains this with: You may see "Our systems have ...
antonio's user avatar
  • 845
13 votes
4 answers
6k views

How does HTTPS help websites under DoS attacks

From time to time one of the websites I browse regularly becomes a victim of a DoS/DDoS attack and usually they solve the problem by switching to https. I cant see the connection between the attack ...
Ulkoma's user avatar
  • 8,773
13 votes
1 answer
11k views

how does a reflection attack work?

I am trying to understand reflection attacks but unfortunately wikipedia is too vague. I understand that in such an attack the attacker tries to authenticate with the target but does so in such a way ...
bernie2436's user avatar
  • 1,457
13 votes
2 answers
10k views

Anti-DoS WebSockets Best Practices

What are the best practices for thwarting DoS attacks for a WebSocket server? Is there a comprehensive site or document that can be referenced?
user avatar
13 votes
4 answers
15k views

How to perform a proper DDoS test in a safe and controlled way?

What is the proper and safe way to perform a DDoS test without crashing the whole infrastructure? What different types of DDoS attacks are there and what things should be considered performing such a ...
Bob Ortiz's user avatar
  • 6,665
13 votes
2 answers
5k views

Zlib DEFLATE decompression bomb

Can you give me an example of a short data string that, when decompressed using Zlib's DEFLATE method, expands to something much much longer? More precisely: what is the nastiest decompression bomb ...
D.W.'s user avatar
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13 votes
5 answers
5k views

Apache/Linux server, DoS attack from own IP

I have an unusual problem I've been trying to diagnose for a while: It's about a Debian server running a custom compile of apache 2.2 with PHP, Red5, MySQL 5.5 (standard binary), sendmail (distro ...
Mantriur's user avatar
  • 233
12 votes
4 answers
8k views

mitigating anonymous DOS (tor combined with pyloris)

I found this rather scary video in youtube, that takes DOS to a whole new level, by making it look like coming from multiple sources. As a counter measure to Rsnake (Robert Hansen) slowloris.py script,...
Tawfik Khalifeh's user avatar
12 votes
4 answers
966 views

What lessons about Denial of Service can we learn from Egypt's "experiment"?

Internet service was widely disrupted in Egypt starting Jan 27th at about 22:15 UTC, in the space of about 20 minutes: How Egypt Killed the Internet. Service was largely restored 5 1/2 days later on ...
nealmcb's user avatar
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12 votes
1 answer
2k views

Can/do botnets brute force "high value" users of services like Gmail?

On an intranet a login is generally disabled after a very small number of failed logins. But a public email service like Gmail can't do the same, otherwise pranksters would just be continuously ...
George Hawkins's user avatar
11 votes
4 answers
2k views

Defending against DoS via product reservation

An e-commerce site should reserve products for a user while they're going through the payment process (more info). This creates a potential denial-of-service risk where an attacker could reserve many ...
paj28's user avatar
  • 33.4k
11 votes
3 answers
20k views

How to protect myself against paid DDoS services?

I am domestic user and I am getting attacked regularly by a guy that hates me. Here is the background story: that guy uses Skype resolvers (tools offered by paid DDoS services) to find out my IP ...
IneedHelp's user avatar
  • 213
11 votes
3 answers
45k views

What are HTTP GET/POST flood attacks?

I want to know what the main differences are between HTTP GET and POST flood attacks and mitigation strategies for both. I searched a lot but I really can't find some good articles nor examples about ...
user19775's user avatar
  • 191
11 votes
2 answers
8k views

Understanding Layer 7 DoS

I recently read this article about how a lone hacker (The Jester) conducts, amongst various other things, his DoS attacks over layer 7 instead of layer 4. It also mentions at one point he was able to ...
XOR's user avatar
  • 235
11 votes
1 answer
8k views

Difference between Amplification and Reflection Attack?

Reflection Attack: Reflection attacks are attacks that use the same protocol in both directions. The attacker spoofs the victim’s IP address and sends a request for information via UDP to servers ...
arif's user avatar
  • 1,156
11 votes
4 answers
7k views

How dangerous is it to allow arbitrary webhook urls to post to?

I am building a Ruby on Rails API that posts to webhooks that the API user can create, whenever a resource that he manages is created, updated or destroyed, using the HTTParty gem. This got me ...
Dennis Hackethal's user avatar
11 votes
4 answers
2k views

What are the drawbacks of login request throttling?

In a web application, one way to protect against password guessing attacks is to lock out accounts after a set number of failed logins. This could be done on both source IP address and username. For ...
SilverlightFox's user avatar
11 votes
4 answers
32k views

Can someone launch a DOS attack on my IP

Suppose, I have a static IP on my PC and is known to others. None of my softwares listen for remote connection. Is it still possible for someone to DOS attack me in such cases? If yes, how it is ...
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