When users visit your website, they trust that their data is secure and that they and other users cannot access files or folders that they are not authorized to see. However, if your website is vulnerable to directory traversal, attackers can exploit this weakness to move from one directory to another and view sensitive files that should be restricted.

These attacks take advantage of a vulnerability in your website's file system and can expose critical information, leading to serious security risks. In this article, we'll explore what directory traversal attacks are, why they are so dangerous, and how you can protect your website from them.

What Is Directory Traversal?

Directory traversal is also known as path traversal or directory climbing. It is a vulnerability in websites where the attacker is able to access or read files outside the web server's root directory running the application by manipulating the web application's input.

When a directory traversal attack is carried out, attackers are able to read and sometimes even make changes to restricted files and directories on the web application server. They may be able to access confidential files on the server like database configuration files, source code files, password files, and log files.

Directory Traversal and the CIA Triad

A directory traversal compromises all three aspects of what's known as the CIA triad. The CIA triad, which is a widely recognized model for information security, stands for Confidentiality, Integrity, and Availability.

Confidentiality

Directory traversal attacks breach confidentiality because restricted and sensitive files containing information about the system and other users become accessible to the attacker. All information that does not belong to a user should be kept secret and should not be accessible to unauthorized persons. For example, an attacker gaining access to the database of users and their personal identifiable information (PIIs), breaches the confidentiality of the system and the user's data.

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Integrity

It is important to note that a directory traversal might not just stop with the cyberattackers being able to read and access files on your web server. If the file system permissions on your server are not configured properly, the hacker may be able to modify or delete important files or directories on the server, compromising the integrity of the data on that server. For example, the attacker may be able to modify a configuration file to grant themselves administrative access to the server or delete system files.

Availability

There are many ways an attacker can use the directory traversal attack to compromise the availability of your server. One example is deleting critical files on the server that disrupts the operation of the server or causes the web application to become unresponsive. Another example is the attacker escalating privileges and overloading the server with requests causing it to crash.

How Does a Directory Traversal Attack Work?

A directory traversal attack can occur in various ways. When attackers suspect that a website is vulnerable to directory traversal attacks, they begin to craft malicious requests to send to that web application.

Some websites display files via the URL parameter. Take, for instance, this website URL: https://www.website.com/download_file.php?filename=file.pdf. This means that the web application is calling the "file.pdf" file from the server using a relative URL path. In this case, the application is reading from the path: www/var/documents/file.pdf.

A simple example of a directory traversal attack is the dotdotslash directory traversal attack. In UNIX and Windows systems, the ../ symbols are used to go back one directory. The attacker may replace the document name with ../../../../../etc/passwd. The URL then looks like this: https://www.website.com/download_file.php?filename=../../../../../etc/passwd

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An attacker could use this payload in the web application to traverse multiple directories backward to attempt to retrieve the "/etc/passwd" file from the server's file system.

In Unix-based systems, the "/etc/passwd" file is a plain text file that contains information about local user accounts on the system, such as usernames, user IDs, home directories, and shell preferences. Access to this file can be useful for attackers because it can provide information about potential user accounts and vulnerabilities in the system.

Other forms of directory traversal attacks include URL encoding, double encoding, and null byte attacks.

Why Are Directory Traversal Attacks So Dangerous?

Directory traversal attacks are considered very dangerous because they are almost never standalone attacks. A directory traversal vulnerability when exploited could lead to multiple other vulnerabilities. Some of these vulnerabilities include:

Information Disclosure

Information disclosure occurs when an attacker gains access to sensitive information that they aren't authorized to see. Directory traversal attacks can lead to information disclosure vulnerabilities because they allow attackers to access files and directories outside the intended scope of a web application. By using directory traversal payloads and malicious requests, attackers can climb up the directory hierarchy to potentially access sensitive files and directories on a server. This vulnerability can be exploited to extract sensitive information such as passwords or user data.

Local File Inclusion

Directory traversal can also lead to local file inclusion (LFI) attacks. LFI is a vulnerability in web applications that allows an attacker to include and execute files that are stored on the same server as the web application In an LFI attack, an attacker can use a web application's input parameters to specify a local file path, which is then included by the web application without proper validation. This allows an attacker to execute arbitrary code, view sensitive information, or manipulate the behavior of the application.

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How Can You Prevent a Directory Traversal Attack?

For starters, validate user input before processing it to ensure that it only contains the expected characters and does not contain any special characters or path separators. Another recommendation is to use filters and whitelisted permitted values to compare user input and block suspicious values. But all these methods could be circumvented by an experienced hacker.

The best approach to preventing directory traversal attacks is to avoid allowing users to supply input to the file system altogether.

Take a Proactive Approach to Your Security

There are a lot of vulnerabilities in the cyber ecosystem. To secure your assets from vulnerabilities, you should carry out regular security assessments and penetration testing to identify potential weaknesses and address them before they can be exploited by attackers.

Additionally, stay up-to-date with the latest security patches and updates for your software and systems, as many vulnerabilities can be patched with these updates. By taking a proactive approach to cybersecurity, you can help to ensure that your organization's assets are protected against vulnerabilities and remain secure from cyber threats.