Penetration Testing Services, by Shorebreak Security

Server Side Includes – All You Need to Know About SSI

Today’s digital infrastructure is more complex than ever before, and servers play a critical role in that infrastructure. From web servers dedicated to hosting websites and applications to specialized email servers that handle mail delivery, servers are the backbone of modern computing and are an integral part of any data center. And while server hardware and software have come a long way in recent years, they’re not perfect.

In fact, servers are often the target of attacks due to the sensitive data they store and the valuable resources they provide. One type of server that is particularly vulnerable to attack is the web server. Web servers are responsible for hosting websites and web applications, and they are often the target of attacks due to the sensitive data they store and the valuable resources they provide. One type of attack that can be particularly devastating to web servers is a server-side include (SSI) attack. So, what is a server-side include attack? How does it work? And how can you protect your web server from it? Keep reading to find out.

What Is a Server Side Include?

If you’re not familiar with server-side includes (SSIs), they are a way to add dynamic content to your website. They can be used in conjunction with other technologies, like PHP or Ruby on Rails, but they can also work on their own.

The technology is relatively simple: when you add an SSI tag to your page’s code, it tells the server to pull information from another file and insert it into the current file as if it were just another part of the page. That way, you don’t have to write out all of the same information over and over again for every page on your site—you just have to write it once in the .shtml file and then include that file wherever you want its contents to appear on your pages.

That’s how it works in theory, anyway. But there are some things you might not know about SSIs that will help you get more out of them if you know what they are before using them in practice!

How Does Server Side Include Work?

It’s not magic: there’s nothing inherently different about an SSI file other than how it’s referenced by your server. When you add a file to your site, it’s stored in a directory on your server. When you want to reference that file with an SSI link, the server looks for the relevant files in the same directory as where it found the .shtml or .html file that calls for them (so if your SSI file is called “foo.shtml” and your main site page is called something like “index.html”, make sure they’re both in the same folder). Then, once it finds all of those files, it combines them into one page before sending it back to you—and that’s how you get dynamic content on your pages without having to write any code!

The Problem – Server-Side Includes (SSI) Injection

In the world of web development and coding, there are many things that can go wrong when you’re building a site. But one of the most common problems is server-side includes (SSI) injection. If you don’t know how to deal with this issue, it can result in some pretty serious security breaches on your site—so it’s definitely something you want to learn how to handle!

What Is SSI Injection?

SSI injection is when someone uses malicious code to break into your site and insert their own code into the file being processed by the server. As you might imagine, this can result in all kinds of trouble—especially if they’re able to use it to get access to sensitive information or do something destructive like delete files or databases.

4 Ways to Defend Against SSI Injection Attacks?

Now that we have understood what an SSI injection attack is and how it works, let’s look at some ways that you can defend against them.

1. Filtering Inputs

As we’ve seen, one of the most common ways to get past security measures is by manipulating input values into something that they aren’t supposed to be. So, one of the best ways to protect against this kind of attack is by filtering user-provided data before it can be processed by your site’s server or database.

2. Using Escape Characters

Another way to protect against SSI injection attacks is by using escape characters in your HTML code. These are special characters that are used to tell the server that whatever comes after them should not be interpreted as HTML, but rather treated as a literal string of text instead. The most common escape character is the ampersand (&), which is used to tell the server that whatever comes after it should be treated as a literal string of text instead of being interpreted as HTML. So, if you want to include an ampersand in your code, you have to use the escape character before it like this: &.

3. Don’t Use Server Side Includes

If you’re looking for a way to defend against server side includes injection attacks, don’t use server side includes.

This may seem like a strange answer, but it’s actually the best one.

Server side includes are the most common way to implement dynamic content in web pages, but they also introduce a huge vulnerability into your website. If an attacker can get access to your .shtml files, then they can inject malicious code into them. This is especially dangerous if you are using PHP or other languages to generate dynamic content because those languages are more vulnerable to injection attacks than HTML is (which is already pretty vulnerable).

4. Never Mix User Inputs and SSI Pages

While it’s important to understand how SSI injection works, don’t forget that the best way to protect your web application from this type of attack is to avoid mixing user inputs with SSI pages. This means that you should never use user data in an SSI page.

Even if you’re using a safe input filter like those provided by PHP, it’s still possible for an attacker to trick your application into running malicious code. For example, an attacker could submit a URL containing something like “../../../etc/passwd” as a file name. This would cause your application to run a program named passwd (the etc directory contains a program named passwd) instead of displaying the contents of the file called passwd.

The Conclusion

Hopefully, these tips will help you avoid SSI injection attacks and make your applications a little more secure. If you have any questions, feel free to drop us a line!