Ever wondered why some individuals and organizations pay great attention to their web applications? They understand that failure to prioritize the security of their networks is an invitation to cyberattackers to come in and cause damages.
And one of the ways that these attackers penetrate a network is through Remote File Inclusion (RFI) attacks.
RFI attacks are quite common and can be executed on targeted websites easily. You sure don't want to be on the receiving end of the attack. In this article, you will learn how to prevent it.
What Is Remote File Inclusion (RFI)?
Remote file inclusion is a technique used to exploit websites and web applications. It preys on inadequate input validation vulnerabilities.
With such loopholes of insight, the attacker adds malicious remote files to web pages and applications. This can only be possible for web applications that accept external scripts and files dynamically.
RFI attacks are quite dangerous because they can lead to loss of sensitive information, cross-site scripting, remote code execution, and a full system override.
RFI attacks result in more than 25% of malicious sessions on websites and are more common than other forms of attack like cross-site scripting and SQL injections.
A major factor responsible for the prevalence of RFI attacks is the absence of healthy cybersecurity practices to enhance the security of web applications.
How Does Remote File Inclusion Work?
A remote file inclusion happens when a file from a remote web server is added to a web page. This allows the attacker to display content from a web application.
RFI also occurs when there is a misconfiguration of the programming code, leaving a vulnerability that attackers can leverage to penetrate your system. Web applications written with PHP codes are more vulnerable to RFI attacks than others. PHP includes functions that promote remote file inclusion. In the case of other languages, it takes a series of steps to allow such vulnerability.
While file inclusion can occur in most web applications, those written in PHP code are more prone to RFI attacks because PHP has native functions that allow remote files, while other languages require workarounds to do the same.
To include a remote file, you need to add a string with the URL of the file to an inclusion function if you're using PHP codes. Otherwise, you'd have to use the equivalent code in your programming language.
When the code is executed, the web server will request the remote file. Once the remote file is included, the web page displays all the contents.
What Is the Impact of an Exploited Remote File Inclusion?
The extent of damage caused by a remote file inclusion attack is dependent on the type of remote file included and the execution permissions given to the web server user.
If the remote file has malicious codes, the web server will execute these codes alongside the webpage content. This makes it possible for attackers to steal sensitive information, hijack web servers and defame web content.
The RFI attack goes beyond the immediate web application security for web servers with administrative privileges to initiate a total system failure.
How to Identify Remote File Inclusion Vulnerabilities
Early detection is an effective defense against cyber threats. The use of intrusion detection systems makes a big difference in averting what could have been a deadly attack. Similarly, detecting the signals of an RFI attack on time saves you from a lot of damages. You have the opportunity to rectify the issue before it escalates.
Running an automated scan with a vulnerability scanner is effective in identifying remote file inclusion vulnerabilities, as it brings pending threats to the fore.
Once the danger is exposed, restrict file inclusion based on user input. But this method may be impossible to implement in some cases. You have to make provision for an allowed list of files to be included.
If you work with a PHP application, you can allow_url_include set off in php.ini for recent installations. This setting helps you to identify vulnerabilities in your network to put up a strong defense.
How to Prevent Remote File Inclusion (RFI) Vulnerabilities
Failure to put measures in place to prevent an RFI attack sets your website up for some serious consequences. These include website content loss, defacing, and exposing sensitive data via your web hosting server.
If you are keen on securing your system against RFI attacks, here's how to go about it.
1. Use Filters to Scrub Input Parameters
Allowing your web server to process all user inputs from HTTP requests increases your vulnerability to RFI attacks. Don't trust any input provided from the HTTP request.
Ensure that all requests are properly examined with the use of filters to check for threats. That way, you can catch malicious requests at the door before they get into your network.
2. Avoid Arbitrary Input Data
One sure way to prevent an RFI attack is to avoid the use of arbitrary input data in a literal file inclusion request. Allowing such input data permissions from users makes your website more prone to receiving a remote file.
Web crawlers and hackers use these input requests to gain unauthorized access to web applications. Instead of allowing just any input, implement a strong and effective access control check before processing user requests.
3. Build a Dynamic Allowlist
A dynamic whitelist is a file created by the user, saved with a filename into a record. Whenever the file is needed, the filename can be used for inputs. Since the filename has already been stored in the record, the webpage can easily verify the file before execution.
Websites that are free from RFI attacks are harder to build than others. This is why we have more websites that are prone to remote file inclusion. But when you check the risks involved in leaving your webpage vulnerable to RFI attack, it's better to build your web pages with a high level of immunity.
Input validation and sanitization can significantly reduce the risk of RFI attacks. You can't be so sure that inputs are completely free from remote file inclusion. Hence, it's necessary to carry out sanitation before execution.
Ensure that the following user-supplied/controlled inputs are sanitized thoroughly before execution.
- Cookie values
- GET/POST parameters
- URL parameters
- HTTP header values
The sanitization process involves checking input fields with an allowlist. Blocklist validation is hardly used because it's weak and doesn't scrutinize input in hexadecimal or encoded formats. This allows attackers to use different formats to supply input files that give room for RFI attacks.
Take Charge of Your Cybersecurity
Remote file inclusion is an attacker's strategy to steal or erase sensitive data from your web application. Depending on the attacker's motive, the attack can be fatal.
Understandably, even the most secure web applications develop vulnerabilities. The difference lies in their ability to resolve potential threats before they escalate.
Remote file inclusion vulnerabilities can be an opportunity for you to strengthen the security of your network if you are on top of your security game.