DoS stands for ‘Denial of Service’. What this means is that someone plans to deny service to and from a website by crashing it, or making it run so poorly that it may as well be offline. As for ‘why’, there are many reasons – someone could be ‘disagreeing’ with the content of the website or it’s discussions, they may be attempting to drive viewers elsewhere, it may be political, it may be simple trolling, the list goes on.
So, how is it done?
The How
Denial of Service is just that: a denial of service. Any means may be used to get to that point. If it’s a poorly secured website, getting in via hacking or password stuffing and changing the contents on-site could be a DoS. If it’s a poorly balanced website, and if it’s one that allows for posting of pictures and memes, sending an image that’s too large for the website to handle could do it. Similarly, sending too much text, animate gifs, or other content that the website wasn’t prepared for could shut it down. Requesting too much data and opening several tabs at once of a big image that did load could simulate an http attack, although that may be equally hard on the computer that’s doing the requesting.
Inputting code into poorly made text entry spots can also crash the website, if the owner didn’t know how to prevent SQL injections. Dinging the website too many times in one go can crash some websites, although that usually requires things like bot nets, which turns it from a DoS to a DDoS.
In that same family, SYN flood attacks can also deny service by requesting information over and over until the website is so overloaded that it can’t respond. In a SYN flood, the computer sends requests to connect to the server repeatedly, but never actually completes them. If it’s done right, the server runs out of ports to take the requests, and legitimate requests mixed in with the faulty ones now have to wait much longer.
Preventing it
Many of these are simple issues of preventing out-of-format content. If a posting box has a hard limit of 10,000 characters, the DoSer could whip up a bot to post over and over, but the website owner would be able to tell that something was going on before it crashes the website. Many picture printing places won’t allow photos over a certain size or resolution to be sent over the web, because it can clog the intake – especially places like drugstores that aren’t set up for large high-quality images. If the network isn’t prepared, it’s entirely possible for photographers to DoS them (at least in the photo station) by accident! Instead, it’s much easier to keep these incidents out at the gate: configuring comment sections and image requirements for size is a bare minimum.
As far as SQL injections go, we have a whole article on sanitizing inputs (here) – the essence of prevention is keeping data inputs and the command to get it to the database separate from each other. This prevents a number of issues by itself, but is good advice to avoid DoSing via SQL as well.
For SYN floods and other brute-force attacks, configuring the firewall and installing an IPS (Intrusion Prevention Software) are what security vendor PurpleSec recommends. In the olden days, attacks like these may not have crashed the site, but they could still drive the hosting costs through the roof – the owner is then incentivized to pull the plug themselves so they don’t drown in fees from their server company.
To prevent breaches, use two-factor authentication when building your site. Please. Microsoft reports that it stops 99.9% of fraudulent login attempts. It is one of the easiest ways to improve your security.
How is it different from DDoSing?
DDoSing relies on multiple computers to get the desired effect; DoSing takes much fewer. This has many benefits for the person trying to wreck a website. Firstly, DoSing doesn’t involve gathering other computers to attack with – you already have all your resources at your fingertips! However, that’s a double-edged sword, as you can’t attack with more than you have.
DoSing is also easier to coordinate as other people are (usually) only minimally involved. Getting other people to DDoS a site organically is difficult because it requires organizing strangers, and doing it with a botnet requires buying a virus or making one yourself and then distributing it. DoSing with a SYN flood or with SQL injections is hard – but it might be easier than trying to get ever-more-wary strangers to click a suspicious link. Outsourcing to a hacker group, of course, is easier than both unless the malicious party lacks the funds to do so.
On the other hand, hacking into a website that’s only password-protected with a password stuffer (or doing it semi-manually by guessing passwords yourself) is probably easier than any other method. While this carries some risk (if they can tell where the login came from, they may be able to find the attacker), it also has a lot of potential for damage if the website owner hasn’t backed up the website. The problem with this method is that the website has to be poorly secured for it to work – 2FA stops the vast majority of these attacks, and being smart with who gets admin permissions can limit the effectiveness of the attack.
Sources: https://purplesec.us/prevent-syn-flood-attack/