Denial of Service (DDoS)

Bare Minimum Application Security

08 January 2013

In this final look at real world threats, it’s time to look at an operational issue, Denial of Service. Previously after introducing the series, we looked at XSS, CSRF, SQLi and most recently, Spammers.

(D)DoS - (Distributed) Denial of Service


An attempt to render your app/service inaccessible or unusable by overwhelming it with bogus requests/connections such that it is incapable of serving legitimate requests/connections.

The Distributed part means that instead of the attack coming from a single source (easily blocked and mitigated against), the attack comes from a huge number of sources (think: botnet) to make blocking/tracing difficult.

Real Example

Imagine a Naughty Hacker adding this to their machine’s cron:

* * * * * curl

Every minute of every day of every year, it’ll request the homepage of insta-SPAM. 1,440 requests per day. No big deal, we can handle that. Now let’s say NH adds this to the cron on 250,000 machines they control through a botnet. 360,000,000 requests per day. Little bit trickier to handle. Now let’s say they actually run a script that hits a URL on insta-SPAM that causes the server to return a 500 error. That’s more taxing than just returning a known page. 360m requests every day using resources due to an error condition. Where are we hosting Insta-SPAM? AWS? Heroku? Hope I’m not paying that bill!

So, protecting against this risk. First, caching. Cache your pages wherever possible. Cache them at a third party like Akamai if you can. Monitor access and drop traffic from IPs that are sending a high volume of requests, not in keeping with your normal app usage. Avoid exposing any endpoint in your app that takes a long time to respond (indicating that it is doing something intensive).

Why you should care:

Availability is key. If a user can’t access your app, they won’t use it. If they don’t use it, they won’t realize it’s the greatest thing ever. Ergo, they won’t come back. Want to raise capital? Great, enjoy explaining why the investor who was super excited about pouring in money to your startup can’t pull up your homepage, never mind the cool parts of your app that would have sold him/her on its promise.

How to detect if someone is trying to attack you

Massive spikes in traffic. Yes, you may have hit the homepage of Hacker News. Yes, your viral marketing campaign may have hit the spot. But be realistic. Is there any logical explanation for a 1000% increase in traffic? Look at the types of requests you’re seeing. Look at where they’re coming from.

Non-security benefits of protecting yourself from this threat

(D)DoS mitigation is often considered an operational task versus a security one, because essentially you’re ensuring your app can handle massive amounts of traffic. Get these steps right, and once you’ve scaled to a billion users, you’re going to be well equipped to serve them.

End of Series

So that concludes our high level overview of the specific threats you’ll face from day one, potentially.

And, as a reminder - I will continue to repeat a disclaimer throughout: This is a barebones, do this rather than do nothing set of suggested approaches. THIS DOES NOT CONSTITUTE ROBUST, COMPLETE AND FOOLPROOF SECURITY. The goal of this effort is to provide non-security aware founders/hackers/developers/etc with a modicum of protection at a stage in the company’s growth where there are no budgets, let alone one for Information Security. The caveat is that as soon as the company experiences growth, one of their top priorities should be to mature in to a properly developed, professionally and thoroughly provisioned Information Security program, specific to their application, industry and environment.

Just as you scaffold certain items while doing rapid coding development, this is your scaffolded application security program. Think of it as the Twitter Bootstrap of web application security.

Your Feedback / Dissent

In creating this, my aim is to improve Application Security in the early stage companies that will often consider the topic "something we'll get to when we scale". As such, critiques, comments, dissenting opinions and any other type of feedback is welcomed and indeed, heartily encouraged.

Constructive feedback will be reflected in the posts themselves at the most relevant points.

If you've got feedback for me, or you have questions about how to apply this to your own startup / project, you can get in touch:

Twitter: @davefromreading

Email: [email protected]