Website security is an increasingly critical issue in today's digital landscape. You will frequently need to safeguard your web applications and systems to keep cybercriminals at bay. Directory traversal vulnerabilities are software security issues commonly exploited by attackers as they try to gain access to your sensitive data.

This post delves into the world of directory traversal vulnerabilities, exploring how they work, the security issues that trigger them, and the appropriate preventive measures. Read on!

Path traversal or directory climbing, commonly known as directory traversal, is a web application server vulnerability that gives cybercriminals access to restricted directories. Attackers often exploit it through HTTP requests, typically by manipulating URLs or other parameters in the request to traverse directories and access unauthorized files.

A successful directory traversal attack can have serious consequences, ranging from unauthorized access to sensitive data to the total compromise of a system. To effectively control or mitigate such attacks, you must have a proactive and defensive mindset. But first, you have to understand how they come about.

Every web server implements security on two levels:

● Access control lists. This level permits access, modifies, or executes arbitrary files on the server. It normally comprises the users or groups with their permission list.
● Root directory restriction. Under this level, users are denied access to files outside Webroot.


During a directory traversal attack, a hacker normally uses guesswork to get paths to sensitive files outside the server. However, more experienced hackers can easily target inadequately protected servers by searching the directory tree.

To perform a directory traversal attack, an attacker only needs a few resources, including the following:
● Access to a web browser
● Insight on where to find the relevant directories
● Basic understanding of Hyper-Text-Transfer-Protocols (HTTP) requests

Once an attacker gets access to the root directory, they can freely maneuver throughout the other sections of the computer system. They can also read and write arbitrary files, giving them the power to modify applications and associated data, view sensitive details like passwords, or dominate the server.

Cybercriminals could also take control of access control lists (ACLs), which administrators normally use to regulate the files that users can access. Attackers can use their access to ACLs to impersonate privileged system users and cause harm.

Several website security issues allow threat actors to successfully conduct directory traversal attacks, including the following:

Unsanitized User Input
When a website accepts user input, such as file names or paths, without proper validation, it becomes susceptible to cyber attacks. Hackers also use special characters (like "../"), which they inject into the input to traverse directories. This is the most common type of path traversal attack that allows hackers to navigate outside the permitted directory and reach unauthorized files.

Insecure File Path Construction
Security vulnerabilities can arise when websites construct file paths by concatenating predefined paths with user input. If the user input is not validated properly, hackers can alter it to point to files or directories they are not authorized to access.

Missing Path Validation
Proper validation of all file paths is necessary at all times, even when user input is not directly used to build the paths. Failure to validate paths can allow attackers to exploit vulnerabilities in the code that processes paths, leading to directory traversal attacks.

Unrestricted File Upload Functionality
Websites that allow users to upload files could inadvertently facilitate directory traversal vulnerabilities. Hackers typically upload files with malicious names containing the traversal sequences they need to access restricted sections of the server.

Insecure Web Server Configuration
Hackers can exploit vulnerabilities that arise due to poorly configured web servers and execute path traversal attacks. Misconfiguring access controls or enabling directory listings, for instance, can give attackers extra information that they use to better exploit your servers.

Below are the two main ways to manually check for directory traversal vulnerabilities:

1. Input vector enumeration. By conducting enumeration, a tester can detect the sections of a web application that may be at a massive risk of attempts to bypass input validation. They identify the application segments that accept user input, including Hypertext Markup Language forms, file uploads, as well as POST and GET calls.
2. Common patterns. Security experts can examine an application's URL structure to check for common patterns that are signs of directory traversal vulnerabilities. Attackers could, for instance, manipulate a query string parameter used to specify the file path to get to restricted files. They could also use search engines to identify URLs that are likely to have file names embedded within.

You can also use automated tools to check for directory traversal vulnerabilities. These tools primarily utilize the following testing tactics:

● Static application security testing. This is where the checkers review the source code for risks while the application is not running.
● Dynamic application security testing. This involves the checkers reviewing the code for risks while the application is still running. The tools never access the source code throughout the process of dynamic testing since they use black box testing to conduct the tests through the front end of the application. One such test is fuzz testing, which relies on malformed data to uncover path traversal vulnerabilities.

To mitigate against and prevent directory traversal vulnerabilities, you need a combination of secure coding tactics, correct configuration, and security measures at various stages of the application stack.

Below are some practices that help to prevent and mitigate them:

Input Validation and Sanitization
You have to validate and sanitize every user input, particularly those used to build directories or file paths. Reject inputs with suspicious characters, such as "../", or other sequences that present traversal risks.

Canonicalization
With the use of canonicalization files and libraries, you can transform the paths users supply into their absolute, normalized versions. This way, attempts to get into directories using ".." sequences are stopped.

Access Controls and Permissions
When your files and directories are protected using strict access controls, you can effectively limit the level of access that various web applications have. The principle of least privilege is beneficial here, as it ensures that web applications can only access the files and directories necessary for their operations.

Web Application Firewall (WAF)
Deploying a Web Application Firewall (WAF) could help detect and block directory traversal attacks. Many WAFs have rules specifically designed to spot and thwart these types of attacks.

Security Hardening
Your operating system and web server can greatly benefit from security hardening practices. The most practical tactics to implement here include disabling unnecessary services, using chroot environments, and configuring file permissions.

Whitelisting and Proper Input Handling
Rather than blacklisting malicious characters or sequences, it is more prudent to use white lists to specify the permitted characters and paths. With its chances for fewer errors and enhanced robustness, this approach is better at protecting your applications and servers.

Run With Limited Privileges
One of the best ways to limit the potential of successful directory traversal vulnerabilities is to run your web application with the least privilege necessary. You should also avoid running it with administrator or superuser privileges.

Logging and Monitoring
Proper logging and monitoring are essential to spot and respond to suspicious activities, such as unusual file access patterns and multiple failed access attempts. Monitor the logs frequently for indications of directory traversal vulnerabilities.

Regular Security Testing
Routine testing can help you spot and remediate directory traversal vulnerabilities. You can conduct code testing reviews and penetration testing using automated tools to identify common issues and get a general overview of your security posture.

Use of Libraries and Frameworks
You should always strive to use well-established libraries and frameworks to construct paths and handle files. The built-in security mechanisms that these libraries have will come in handy.

Education and Training
Your development team should have full knowledge of directory traversal attacks and why they need to use secure coding tactics. They should also know about the potential consequences so they always adhere to secure coding guidelines.

Directory traversal vulnerabilities pose a considerable risk to the security of servers and applications. To protect your applications and users from potential data breaches, unauthorized access to sensitive data, or system compromise, you have to understand how these vulnerabilities are exploited and implement preventive measures. To do this effectively, you need a platform that is dedicated to detecting and blocking malicious requests.

Here's how a ThreatSign's WAF can help:

● Signature-based detection. ThreatSign's WAF maintains a database of known attacks and immediately blocks these signatures, even when they are slightly obfuscated.
● Pattern matching. ThreatSign's WAF analyzes incoming HTTP requests and effectively blocks responses for patterns with hints of software security vulnerability.
● Request filtering. ThreatSign's advanced filtering rules can also be customized to match potential attack vectors or the specific application's characteristics.

Overall, ThreatSign! offers a superb layer of protection against directory traversal vulnerabilities and effectively safeguards your applications and users. You should use it alongside other security mechanisms, such as regular security audits and secure coding practices for all-around protection against web application and server breaches.

Sign up for ThreatSign! today to get started.