Tuesday, October 27, 2015

Security Month - Episode 1: Injection

Starting With A Bang


Injection attacks, in all their various flavors, are now the number one most exploited security flaw in software. Their impact can range from something as innocuous as displaying extra text on a web page to the full compromise of your host machine.

Setting A Bad Example


Do you see anything wrong with the following snippet of PHP code?
(Note: this is a simplified example for demonstration purposes only)

// Initializes necessary variables, functions, etc.
require_once( "important.libs.php" );


$accessLevel = GetAccessLevel();

<snip>

// Defaults to empty string if not present
$name = Posted( "name" );

// Find contacts with matching first name in database
$sql = "SELECT * FROM Contacts WHERE ".

       "FirstName = '$name' AND ".
       "AccessLevel <= $accessLevel";
$result = $db->query( $sql );
// We should really do some error checking here

// Print details for each match found
while( $row = $result->fetch_assoc() ) {

    $firstName = $row[ "FirstName" ];
    $lastName = $row[ "LastName" ];
    $phone = $row[ "Phone" ];

    print "Name: $firstName $lastName, Phone: $phone<br />";

}

<snip> 


As you might have guessed from the title of this article, this code is vulnerable to injection. In fact, it is subject to two common forms of injection: SQL injection, and cross-site scripting (XSS).

What Is Injection?


Injection happens every time we receive input from an untrusted source and submit it to an interpreter without first sanitizing the input. In the case of SQL injection, that interpreter is the database interpreting the text of our SQL query. In the case of cross-site scripting, the interpreter is the browser attempting to display our HTML page. Whatever the scenario, allowing potentially dangerous user input to be interpreted as a trusted command or request can have disastrous .consequences.

What Could Go Wrong?


In the scenario above, imagine that a hacker wants to get a list of all contacts in the database. They are currently restricted only to those contacts whose AccessLevel value is lower than a configured value. How could they use SQL Injection to gain access to everything?

What if, in the form that requests this page, they entered "' OR 1 --" as the name to search? What would our query look like now? (Assuming AccessLevel = 2)

SELECT * FROM Contacts WHERE FirstName = '' OR 1 --' AND AccessLevel <= 2

With a new terminating quote and comment, suddenly our query is changed to be much more permissive. The attacker has tricked our script into revealing more information than intended. What if instead of a SELECT, we were working with a DELETE query? The entire table full of valuable data might be lost.

The second vulnerability is to a cross-site scripting attack. What if, instead of entering their name, an attacker entered some raw HTML such as "<script>alert('XSS!')</script>"? Suddenly, they've inserted their own elements and even javascript code into your web page. If they can get this to happen on a page displayed to another user, the attacker can hijack your page to show you them anything they want and it will look like it's coming directly from your page.

It Could Be Worse


Imagine a different scenario where input is passed to an exec() call and run on the system. Now instead of limiting damage to the database system, a clever attacker can run commands directly on the server. Depending on the privilege of the process and security of the underlying system, the attacker could potentailly gain root access to the machine. They can use this to access sensitive data, change important settings, or even run any program of their choosing. The entire system can be compromised and placed at the mercy of a malicious hacker.

Don't Forget Secondary Sources


Here's one that can really trip you up. Imagine an application that performs a task based on values stored in the database. It's easy to forget that despite the fact that the database belongs to you, the source of your database values may not always be clean. "We've traced the call, and it's coming from inside the house." Always assume any source of data is dangerous unless you can verify its source and security.

How Can We Fix It?


The good news is that there is a simple way to protect yourself from injection attacks: sanitize user input using readily-available libraries.

If your language of choice is PHP, there's plenty of built in functions to safely encode all varieties of user input:
Please remember that this is not a comprehensive list. There are so many different languages and environments out there. Whenever you're wielding user input, be careful to consider whether your code may be subject to injection attacks and research appropriate measures to counter such attacks.

Where Do We Go From Here?


If you feel this post is yesterday's news, I hope you take it as a friendly reminder and refresher on the topic. If any of this is new to you, I suggest you take the next opportunity to study up on the subject. Read some other blog posts. Follow some examples online. Revisit a piece of recent code and try to break it (in a test environment please!). Once you've found some vulnerable code, learn the proper way to secure it and and run your tests again to prove that it's been fixed.

If there's one thing to take away from this it's this: always treat user input as suspect. Never let raw user input pass from your application to another system without sanitizing it first.

Now go and write some secure code.

Cheers,

Joshua Ganes

Thursday, October 22, 2015

Announcing Amish Programmer Security Month

From Humble Beginnings


I started programming from a young age. I distinctly recall being in grade 5 and being curious about how some of the games in our school's computer lab worked. Having absolutely zero clue, I checked out a book from the school library on programming for the Apple IIe. My first programming experience was typing out Apple BASIC programs straight from the book and watching them fail as my two-fingered hunt-and-peck typing resulted in multiple typos.

My exposure to computers was reasonably limited until my sister and I pooled our money to buy a 100MHz 486 (with TURBO on for maximum fastness). I'm pretty sure I got the better end of that deal as I began spending a lot of time both playing video games and experimenting with QBASIC and its elaborate but confusing help files.

In high school, I took a few courses in Turbo Pascal and C++ programming. This mostly involved running through a bunch of easy exercises in each chapter and then spending the rest of our class time playing in the lab or working on our frighteningly terrible video game group project. That Pascal text book may be the only high school textbook that I've ever read from cover to cover.

After puttinsg four years of university and another year's paid internship under my belt, I was sure that I knew almost everything I would ever need to know as a professional software developer. I had no idea just how much more I still had to learn...

What Do You Mean This Is Insecure?


With so many courses behind me, I was sure that I had covered most of the important topics. If security was so important and difficult, surely someone would have covered it in one of my course by now. I was surprised when one of my colleagues pointed out security flaws in my code. I did not even recognize it as a flaw when it was pointed out to me.

Over time, with the help of more experienced mentors, bloggers, and some job-sponsored training, I began to learn a lot more about secure coding techniques. For many of my experienced readers, these have likely become second nature. Still, everyone can stand a refresher on the basics now and again. For those who, like I once was, may still be in the dark about secure coding, you have a great deal to learn.

Amish Programmer Security Month


With that in mind, I declare the next month to be security month here at Amish Programmer. I will strive to get back on board the posting train and publish a brief post covering such security topics as injection, buffer overflows, and more.

These topics have all been covered in depth by others. I will try to present a fresh take on these topics using code snippets and straightforward examples. You can tune in in the coming weeks for a short discussion of several fundamental topics in secure coding. I hope to see you back here soon.

Cheers,

Joshua Ganes

Wednesday, October 14, 2015

Challenge Your Assumptions

Today's brief post was inspired by my recent road trip with my wife from here in Vancouver, BC through the states of Washington and Oregon.

When it comes to road trips, I'm all about efficiency. Pit stops run like clockwork. The guys from NASCAR have nothing on me. That's why I prefer self service with pay-at-the-pump when stopping for gas. My fingers fly with precision as I fetch my card from my wallet, insert it in the machine and punch my way through the menu to start up the pump and select my grade of gasoline to begin fueling.

On my first stop of the trip, everything was running smoothly right up until I was stopped in my tracks by the following prompt:

Enter Zip Code:

 

Cancel         OK

Unfortunately for me, as a Canadian, I don't have a numeric 5-digit zip code. Instead, I have a six character postal code with a mix of numbers and letters. Try though I might, I could not find a way to enter my postal code or skip this prompt.

Edit: I've since been told that you can simply enter the numeric portion of your postal code followed by zeros

After a few moments of poking around at the machine, I eventually resorted to pressing cancel and walked into the station to speak with the cashier. Within a few minutes I was back on track (a lap behind the race leaders).

My experience with the zip code prompt was hardly life altering. Still, it illustrates some of the problems that can come up when your software makes incorrect assumptions (e.g. all gas station customers have a zip code). Challenge your assumptions and do your best to consider all possible users. Question whether all the information you prompt for will be available or match your expected format. If not, your software should gently guide the user on how to proceed.

Cheers,

Joshua Ganes 

P.S. Did you see the seventh inning of today's Blue Jays vs. Rangers game? It was well worth a second look! Go Jays!