Directory traversal attacks

By
Manieendar Mohan
Published on
26 Mar 2024
7 min read
Vulnerability

Directory traversal, also known as path traversal or directory climbing, is a security vulnerability that occurs when an attacker can access files and directories outside of the web application’s intended directory structure.

This vulnerability can lead to unauthorized access to sensitive files, data leakage, and potentially the execution of malicious code.

Directory traversal allows an attacker to access files outside the Webroot folder through HTTP communication.

An attacker can get access to sensitive information and can execute arbitrary codes on the server. Usually, every web server implements security on 2 levels:

  • Access control lists: The access control list is used to give access, modify or execute arbitrary files on the server. The list consists of the users or groups with their permission list.

  • Root directory restriction: Under this restriction, the users are not allowed to access any files outside Webroot. Directory traversal attack is also called ../ (dot dot slash) attack, directory climbing, or backtracking attack. The cause of the directory traversal attack might be a flaw in the code.

If an attacker successfully exploits a server using a directory traversal attack, he will be able to access sensitive files outside the server.

The attacker could access files like passwords to get the username and passwords of all the users in the application.

A successful directory traversal attack can have enormous consequences from loss of sensitive information to total server takeover.

Example

If the following URL works, then the website is vulnerable to a directory traversal attack.

http://example.beagleexample.com/getUserProfile.jsp?item=../../../../etc/passwd

The above URL will give the attacker access to the passwords on the server.

How do directory traversal attacks work?

Here’s how a directory traversal attack works:

1. User input

The web application accepts user input, typically in the form of URLs, file paths, or parameters, without properly validating or sanitizing the input.

2. Manipulation of paths

The attacker manipulates the input to include sequences like “..” or “../” to navigate up the directory structure.

These sequences are used to move from the current directory to higher-level directories.

3. Access to sensitive files

By including these sequences in the input, the attacker may access files and directories not intended to be publicly accessible.

For example, they might navigate to configuration files, user data, or even system files.

4. Potential exploitation

Depending on the nature of the files and directories accessed, the attacker can exploit the vulnerability in various ways, such as stealing sensitive information, modifying files, or launching further attacks.

A directory traversal attack, when successful, can have significant and potentially severe impacts on a web application, its data, and the overall security of a system.

What are the impacts of directory traversal attacks?

Here are some common impacts:

1. Unauthorized data access

The attacker can access files and directories outside of the intended directory structure.

This can lead to the unauthorized viewing of sensitive data, such as user profiles, configuration files, encryption keys, and more.

2. Data leakage

Sensitive information may be exposed to the attacker, which can result in data breaches.

This information could include personal identifiable information (PII), financial records, health records, or other confidential data.

3. File modification

In some cases, an attacker may be able to modify files outside of the intended directory.

This could lead to data corruption, unauthorized changes to configuration files, or the introduction of malicious scripts into files.

4. Code execution

Depending on the web application’s configuration and permissions, an attacker might use directory traversal to execute malicious code stored in files outside of the application’s root directory.

This could lead to a full system compromise.

5. Bypassing authentication

Directory traversal attacks can sometimes be used to bypass authentication mechanisms.

For example, an attacker might gain access to an admin panel or other restricted areas of the application.

6. System impact

If the web application runs with elevated privileges, a successful directory traversal attack can have a cascading impact on the entire system.

It may lead to unauthorized access to system files and configurations.

7. Reputation damage

A successful attack can damage the reputation of the affected organization, especially if sensitive customer data is exposed.

Trust may erode, leading to customer dissatisfaction and potential legal consequences.

Depending on the data accessed and applicable data protection laws, organizations may face legal penalties and regulatory fines for failing to protect sensitive information.

9. Operational disruption

Security incidents, such as directory traversal attacks, can disrupt normal operations and lead to downtime while the organization investigates and remediates the issue.

10. Resource consumption

An attacker may use directory traversal attacks to consume excessive server resources, potentially leading to denial of service (DoS) conditions.

How can you prevent directory traversal attacks?

Preventing and mitigating directory traversal attacks requires a combination of secure coding practices, proper configuration, and security measures at various levels of the application stack.

Here are steps to help prevent and mitigate directory traversal attacks:

1. Input validation and sanitization

Validate and sanitize all user inputs, especially when they are used to construct file or directory paths. Reject any input that contains suspicious characters like “../” or other traversal sequences.

2. Canonicalization

Use canonicalization functions or libraries to convert user-supplied paths into their absolute, normalized forms.

This ensures that any attempt to traverse directories using “..” sequences is thwarted.

3. Access controls and permissions

Implement strict access controls on files and directories to limit what the web application can access.

Use the principle of least privilege, ensuring that the web application only has permissions to access necessary files and directories.

4. Web application firewall (WAF)

Deploy a Web Application Firewall (WAF) to help detect and block directory traversal attacks. Many WAFs have rules specifically designed to identify and mitigate this type of attack.

5. Security hardening

Apply security hardening practices to your web server and operating system.

This can include configuring file permissions, using chroot environments, and disabling unnecessary services.

6. Whitelisting and proper input handling

Instead of blacklisting dangerous characters or sequences, use whitelists to specify which characters and paths are allowed.

This approach is generally more robust and less error prone.

7. Run with limited privileges

Run your web application with the least privilege necessary.

Avoid running it with superuser or administrator privileges to limit the potential impact of a successful attack.

8. Logging and monitoring

Implement proper logging and monitoring to detect and respond to suspicious activities, such as multiple failed access attempts or unusual file access patterns.

Monitor logs for signs of directory traversal attempts.

9. Regular security testing

Conduct regular security testing, including penetration testing and code reviews, to identify and remediate directory traversal vulnerabilities.

Automated tools such as Beagle Security can help identify common issues while also providing a deep dive into your security posture to avoid breaches.

10. Use libraries and frameworks

Whenever possible, rely on well-established libraries and frameworks for file handling and path construction.

These libraries often have built-in security mechanisms.

11. Education and training

Educate your development team about the risks of directory traversal attacks and the importance of secure coding practices. Ensure that developers are aware of potential consequences and follow secure coding guidelines.

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Written by
Manieendar Mohan
Manieendar Mohan
Cyber Security Lead Engineer
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