What are some fundamentals of security every developer should understand?

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Ben Halpern DEV.TO FOUNDER

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  1. Trust no one. Especially yourself.
  2. The only perfectly secure system is one that's been disconnected, powered off, encased in concrete, and dropped into the ocean from a helicopter flown blindfolded.
  3. Any functionality you can use is functionality someone else with ulterior motives can use. Data you can access through your system is data someone else can access through your system. Backdoors are an inherent security risk.
  4. Assume user input is malicious until proven otherwise.
  5. If you're good enough to roll your own crypto, you already have a job working specifically on crypto.
  6. If you only need to test whether input matches something you've stored (like passwords), hash, don't encrypt.
  7. Bind prepared statements, don't interpolate parameters into queries.
  8. If you have a publicly-visible API backing your site, remember that your site isn't the only thing that can hit it.
  9. Think about and test edge cases.

I'm not sure if the blindfolded helicopter will achieve its purpose. It might just crash pretty quick, make the system fall and release it from concrete. Just sayin'

You can take off without the blindfold but you have to put it on once you're over the water.

  1. Validate input data!
  2. Seriously, validate input data.
  3. Did I mention validating input data?

The less data you store, the fewer security hazards you expose yourself to, and the safer your participants will be. Don't hoard data on the theory that it'll become useful - only save what you need, and question yourself every time you get into a situation where you think you need it.

If you must store data, especially sensitive data, don't ever store it in plain-text! Look into hashing algorithms like bcrypt.

Always give your participants the option to delete their data, and actually delete it when they ask you to.

In Europe we must comply to GDPR which is coming into practise in the next few months. We’ve had to implement what you mentioned on every single system which holds more than one piece of identifying information about a user.

So it's not just a good idea, it's the law ;)

What did you do, just hash or encrypt everything? We are facing the same right now.

Not everything, just database tables containing personally identifiable information. You’ll want to encrypt this information rather than hash it, as you’ll more than likely need to retrieve it at a later date. Here is a good read which explains the legislation in more detail: techblog.bozho.net/gdpr-practical-...

  • Security is hard. It's worthwhile to read about various attacks to understand the magnitude of ways in which stuff is attacked.
  • Your system will be breached. Mitigation strategy is as important as the "wall".
  • A system is never "secure", you can only balance security goals with current risks and available resources.
  • Privacy is inseparable from security. Even if you're irresponsible and don't care about your users, the attackers will.
  • Security becomes harder as the data becomes more valuable. Most systems are really only secure because nobody really wants the data they store. As a company becomes successful, the attackers will come.
  • Security is a moving target. You are are never done implementing security.
  • User security is as important as corporate security.
  • Being open about security is the only way to know it's correct. There is no security through obscurity.
  • Everybody is responsible for security. Every person and every machine is a potential attack vector.

Practical advice:

  • Use existing libraries
  • Follow best practices
  • Keep everything up-to-date
  • Be open and ask questions
  • Code defensively
  • Be aware of risks

The OWASP top ten security vulnerability documents are a great place to start: OWASP. Typically, the top web app security vulnerabilities are SQL injection, XSS and authentication issues. The top web frameworks will address those issues in their documentation so that is another place to begin researching.

Don't roll your own crypto in production.

API Keys are just as sensitive as a username and password combination!

  • Don't expose them in publicly accessible repositories or source code.
  • Do configure them as server environment variables in a contained environment.

I'd add: never even commit a credential (password/API key/etc) to your repo. I'd argue this applies to any repo, not just open source ones, since you never know what might happen to the repo in the future. Even if you remove the credential in a future commit, it still exists in the history.

Yeah too true.

Just FYI if anyone has hit this issue before: ‘Bfg repo cleaner’ can clean the repository of any traces of files, however if you’re working on a team project the key can spread like a virus as it will ‘infect’ branches stemmed off of master in the future (if this passed code review of course). I had to deal with a situation similar to this as someone had committed a global config file containing passwords which was only meant for development. Fun times. Of course the solution for deeming an API key pair useless is just to regenerate the key, however passwords are a different story if you don’t want a history of previous passwords being revealed.

GitHub is pretty good with that, if they detect that one of their keys was committed and pushed to GitHub they'll let you know and disable the key.

Whenever you process data from the outside, always process it in this order:

  1. Sanitize
  2. Validate
  3. Execute
  4. Display feedback

Example:


$errors = array();

// 1. Sanitisation
$email = filter_var($_POST['email'], FILTER_SANITIZE_EMAIL);

// 2. Validation
if (false === filter_var($email, FILTER_VALIDATE_EMAIL)) {
   $errors['email'] =  "Invalid email address";
}

// 3. Exécution
if (count($errors)> 0){
    echo 'There are errors : ';
    print_r($errors);
    exit;
}
// At this point, all is fine, let's open the gate...
$bdd = new PDO('mysql:host=localhost;dbname=test', 'root', '');
//...

// 4. Feedback information

DON'T RUN a command with sudo in your command line if you don't fully know what it's doing & understand that typing sudo in front of a command & then typing in your password grants that command full read/write access to your filesystem!

For example:
I know we've all seen this command before & sometimes jokingly tell people to run it
sudo rm -rf /

What this command does is it recursively remove all files/directories under /. "Slash" is the root directory of your computer. So calling sudo with this command gives it full rights to do without prompting any kind of warning to proceed.

1- Never trust user input. Always validate both frontend and backend
2- Sanitize the data. Use prepared statements
3- Set Access-Control-Allow-Origin to deny
4- Your application must login to the database with the minimum rights as possible.
5- Change the passwords frequently
6- Keep server system up to date
7- Configure the firewall properly
8- Consider to use CDNs
9- Be aware about the data you are dealing.

  1. Do not trust the user.
  2. Social engineering might pawn anyone, not just the non-techies.
  3. Salting is the bare minimum when it comes to storing passwords.
  4. Make your system fail hard, but do not expose critical details when you do so.

Something about not exposing passwords by passing form info as url variables because people can then see your password.

It's not a fundamental principle, but this book was a good overview of security subjects. Unfortunately, as I discovered when studying for my Security+ test, the book is not really designed for cramming. It looks like there's a 6th edition out now.

There's no one stop shop security solution for any application. Security and best practices are always changing and the most important thing in security is showing up and staying informed. And trust no one.

  1. Don't trust any data or code, not even your own. Handle data in its respective context. Handle code as a liability.
  2. If only one small part of your application is insecure, all of it is insecure.
  3. Most attacks are related to side channels, performance and timings, buffer overflows, off-by-one errors or a combination thereof.
  4. In order to secure your code, you must think like an attacker.

The OWASP Top 10 is a start. owasp.org/images/7/72/OWASP_Top_10...

OWASP puts together a list of what they consider the most critical security risks in web applications and is updates every few years to account for trend changes.

Don't forget about social engineering. Tell your support team to never give out passwords over phone. Build a password reset into site and get your support team to point users to that.
Most data breaches are by employees - lock your systems down.
Get your site pen tested.
Plus everything already said.

Dian: Love the helicopter!

Here is my 2-cents to add to your list:

This has some good overlap with your items and a few others to add:

Web Developer Security Checklist: dev.to/powerdowncloud/web-develope...

Read crackstation's hashing and sec "summary" as a primer: crackstation.net/hashing-security.htm

Design and code everything with a 'secure by default' mindset - meaning that out of the box your code should be secure.

It is easier and safer to whitelist than blacklist.

Security is everyone's responsibility even the people who don't write code. Designers can just as easily expose information about people with poorly thought out UX.

Have a shared understanding of threads to your application/product in your team.

Don't assume its anyone else's responsibility!

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