What's Missing In Form Security

One day, a professor came to me with an interesting question: "Corey, my server is getting hacked! Can you figure out how?" "Can you tell me what exactly is happening?" "Yes," he replied. "Somehow, people are uploading files to my server, and trying to hack me." And with that, I delved into the world of form handling (a solved problem, I had assumed), and was appalled at what I found.

This professor was neither unintelligent nor shoddy in programming skills. What he was not, however, was an expert in web security, and therein lies the problem that this post is about. It's not about SQL injection. It's not about using the newest tools or the most recent library. It's about understanding how form submissions can be your Achilles' heel. The professor was qualified in his programming ability, but he was not a web security expert, and you are probably not an expert, either. He was doing everything right, according to the docs and numerous tutorials on how to work with his particular framework, but the information was wrong. The scariest thing is that it's very likely that the framework that you are using is getting it wrong, too.

The Git Logo
Image from git-scm.com.

I have had the opportunity to explain Git and the basics of its operation on more than one occasion. It's something that I enjoy doing, especially because I believe it is an indispensable skill for collaboration in industry and academia. I have always distributed a small "cheat sheet" with the most-used commands, and I am posting it here (for no reason other than I can find it quickly in the future). I will include the text in this post, but I will also provide the .txt file that I use. (Yes, I wrote it in a txt file. I like the way it looks, and when I print it out using Notepad++, the wrapped text is indented nicely.

Spam is bad! Kill it with fire!
Image from openclipart.org.

Due to the irritating nature of spam email, companies have started hardening their policies for how they handle emails that originate from various sources. A recent change that has hurt a lot of sites and mailing lists lately is that email providers have begun to make their DMARC policies very strict. Specifically, email providers are saying, "If the email says that it is from one of our email servers, but it didn't come from our server, then deny the message." (I'm looking at you, Yahoo! and AOL!) This in and of itself is not the whole problem. The recipient email service must agree to respect DMARC policies. When they do, emails that say that they are from a domain, but are from somewhere else, are silently rejected.

"But wait," you say, "this sounds totally reasonable!" You're right. And wrong. And right. Let's just get this sorted out.