Cyber Security

Local File Inclusion (LFI) is a common vulnerability that allows attackers to exploit a web application’s file-handling mechanisms. When an LFI vulnerability exists, an attacker can trick the application into including files from its server, potentially exposing sensitive information or executing malicious code.

But how does LFI actually work, and what makes it so dangerous? Read our detailed guide to learn how LFI operates, its potential impact on your system, and the essential prevention measures to protect your web applications from such attacks!

What is Local File Inclusion (LFI)?

Local file inclusion is a vulnerability in web applications that allows attackers to access, view, or execute files from the server’s file system by exploiting poorly written code.

In such cases, an attacker can manipulate a URL to include files from a server root folder, which might expose sensitive information, source code, or configuration files.

This weakness can also lead to cross-site scripting (XSS) if an attacker can inject a script.

It differs from remote file inclusion, which allows malicious attackers to include files from a remote server and makes it easier to execute remote code.

How Does Local File Inclusion Work?

Local file inclusion occurs when web applications improperly handle user input for file inclusion. Here’s how it typically works:

1. File Inclusion in Web Apps: Developers include server-side files, such as configuration files or user uploads, within their applications using user input parameters.
2. User Input Manipulation: An attacker manipulates these input parameters (e.g., a URL parameter) to specify a file path.
3. File Path Manipulation: If the application fails to validate these inputs properly, the attacker can traverse directories to access files outside the intended folder.
4. File Viewing or Execution: This allows the attacker to view sensitive files, like /etc/passwd, or execute malicious scripts.

For instance, In a PHP-based web application, an LFI vulnerability lets an attacker manipulate the “page” parameter to display sensitive system files or execute harmful code.

Impact of Exploited Local File Inclusion Vulnerabilities

Information Disclosure

Upon a successful LFI, the attacker can see the content of the critical system file. This kind of disclosure gives attackers valuable information for further exploitation.

Directory Traversal

An LFI can lead to a directory transversal when an attacker uses the LFI to navigate through the server’s file system beyond the intended folder.

By entering directory traversal characters like ../, they can access files in parent directories.

For instance, a vulnerable application might use an attacker-supplied path like ../../etc/passwd to retrieve files outside the web root directory, revealing system files and other data.

Remote Code Execution

When combined with a file upload vulnerability, an LFI can lead to remote code execution. This is possible if the attacker can upload a malicious file, like a PHP script, and then include it via the LFI vulnerability.

Once included, the server executes the attacker’s script, allowing them to steal data, deface the site, or gain unauthorized access remotely.

This is more dangerous than information disclosure or directory traversal because it can fully compromise the server.

Finding and Preventing Local File Inclusion (LFI) Vulnerabilities

To find LFI vulnerabilities, consider these approaches:

1. If using third-party software, identify the exact version of the application and check for known vulnerabilities using software composition analysis (SCA) tools or network scanners.
2. Conduct manual testing by inputting various payloads that attempt directory traversal (../) or access unintended files.
3. Use web vulnerability scanners like OWASP ZAP, Burp Suite, Invicti, or Acunetix to automatically detect and potentially exploit LFI vulnerabilities, whether known or unknown.
4. Review your application’s code for unsafe file inclusion practices, particularly where user input is involved.

Meanwhile, to mitigate LFI risks in web applications, developers should follow these steps:

1. Prevent the inclusion of filenames directly from user input or other manipulatable sources like cookies.
2. If file inclusion from user input is necessary, use a whitelist to specify only safe files.
3. When arbitrary filenames are unavoidable, store them securely in a database and use table row identifiers or URL mappings to reference them.
4. Continuously validate and sanitize all user inputs to block harmful characters, like ../, and prevent directory traversal.
5. Disable risky PHP wrappers (php://input, expect://) to prevent their exploitation.
6. Limit server permissions to minimize the impact of potential LFI attacks.
7. Make sure error messages don’t reveal sensitive information about the file system structure to prevent attackers from gaining valuable insights.

Frequently Asked Questions

Conclusion

Local File Inclusion (LFI) is a serious vulnerability that can expose sensitive files and enable malicious code execution on servers. Understanding how LFI works, detecting it with manual testing and automated tools, and implementing prevention strategies like input validation, whitelisting, and secure coding is essential to safeguarding web applications.

Protecting against LFI vulnerabilities is crucial for maintaining a secure environment. Contact Fluxgate today for expert help and a deeper understanding of securing your systems to strengthen your cybersecurity defenses!