Summary
A directory traversal attack, also known as path traversal, is a web-based security vulnerability that allows attackers to access files and directories outside the intended file system structure. This type of attack can expose sensitive application data, credentials, configuration files, and more—posing a serious risk to organizations, especially when exploited through client-side scripts or web apps.
What Is a Directory Traversal or Path Traversal Attack?
A directory traversal attack—also called path traversal—is a code injection vulnerability where a threat actor manipulates input fields (like URLs or file paths) to access unauthorized files and directories on a server. The goal is to “traverse” up the directory tree (e.g., using ../) to reach restricted areas outside the application’s root directory.
How It Works
This attack occurs when a web application dynamically includes file paths based on user input—without proper validation or sanitization. Here’s how it works:
- The attacker enters specially crafted input like ../../../etc/passwd into a file path parameter.
- The application, if not protected, interprets this as a legitimate request.
- It then accesses or exposes unintended files outside the web root.
Common symbols used:
- ../ (move up one directory)
- %2e%2e%2f (URL-encoded version)
If successful, the attacker can read sensitive files, execute arbitrary code, or gain unauthorized access to critical systems.
Who’s at Risk
- Web applications that serve files based on user input (e.g., file downloads, image previews)
- Developers using insecure input handling or custom file inclusion logic
- Organizations using legacy code or third-party scripts that don’t sanitize file paths
- Industries with sensitive data, such as finance, healthcare, or government
Real-World Examples
- Apache Tomcat Vulnerability (CVE-2017-12615): Allowed attackers to upload malicious JSP files and traverse directories on misconfigured systems.
- GoAhead Web Server flaw (CVE-2017-17562): Enabled remote attackers to read arbitrary files via path traversal in URI requests.
- Client-side misuse of file retrieval scripts in modern web apps has led to exposure of internal APIs, logs, and credentials.
How to Detect or Prevent It
Detection Methods:
- Monitor server logs for patterns like ../ or encoded equivalents
- Use dynamic application security testing (DAST) tools
- Leverage client-side threat detection for suspicious DOM-based script activity
Prevention Strategies:
- Always sanitize and validate user input
- Use allowlists for file paths and filenames
- Implement chroot jails or sandboxing to restrict file access
- Disable directory listings on web servers
- Keep frameworks and libraries updated
How Feroot Helps
Feroot’s Client-side Security Platform continuously monitors JavaScript behaviors on the front end to identify vulnerabilities like directory traversal attacks. With script behavior analytics, real-time policy enforcement, and risk scoring, Feroot helps security and dev teams:
- Detect unauthorized file access attempts
- Prevent data exfiltration from malicious third-party scripts
- Enforce secure input handling policies across web apps
FAQ
What’s the difference between directory traversal and file inclusion attacks?
Directory traversal focuses on accessing restricted files via manipulated paths, while file inclusion vulnerabilities often involve injecting malicious files into the app runtime (e.g., LFI or RFI attacks).
Can directory traversal happen on the client side?
Yes, especially in SPAs and modern web apps that use JavaScript to load files dynamically. Feroot helps monitor and block such activity.
What types of files do attackers usually target?
Configuration files (config.php, .env), password files (/etc/passwd), and internal logs are common targets.
How can I test my app for path traversal vulnerabilities?
Use security testing tools like OWASP ZAP, Burp Suite, or custom test payloads like ../../../../etc/passwd to simulate attacks in a safe testing environment.
