Directory Traversal Attack: History, Exploitation, Detection and Prevention

- July 28, 2025

What is the directory traversal?

The directory traversal, also known as the path traversal, is a web safety vulnerability that allows an attacker to reach files and directors stored outside the web root folder. "Dot-Dot-Slash (..)" can cross the attacker directions by manipulating the variables with sequences and their variations, and can access the restricted files-as the application source code, configuration files, or system password files.

Example:

Instead of accessing:

arduino

https://example.com/view?file=about.html

an attacker might try:

bash

https://example.com/view?file=../../../etc/passwd

This could result in access to /etc/passwd on Unix-based systems if the application doesn't sanitize input correctly.

History of directory

The origin of the directory traversal weaknesses goes back to the early days of web development when developers user rely much on the dynamic file path generation based on the input. The early CGI scripts and PHP applications were particularly weak.

Major milestones:

1990s: The initial web server lacked basic input verification, and the CGI script was an easy goal.
2000: Unicode directory traversal vulgarity in Microsoft IIS 4.0 and 5.0 allowed the attackers to execute the command on the server using encoded characters.
2008-2015: A series of open-sources CMS platforms (such as Zoomla, WordPress and Druple) faced the directory traversal exploits.
2019: Fortnite's user accounts were improperly handled due to URL, which was part of the surface of a broad attack.
2021+: With the rise of API and Microservis, inappropriately secure &points have made the directory traverse more fine and difficult.

How does the directory traversal work

At its core, a directory targets targets the user targets inappropriate handling of input when creating the exploitation file path.

Mechanism:

Web applications include dynamic files based on user input.
The input is not sanitize, allowing users to specify the relative path (eg, ../).
The application navigates outside the intended directory and exposes sensitive system files.

Types of Traversal Patterns:

../../../../etc/passwd (Unix/Linux)
..\..\..\..\boot.ini (Windows)
URL-encoded: %2e%2e%2f (represents ../)
Double URL encoding: %252e%252e%252f

How to Exploit Directory Traversal

Step-by-Step Exploitation Process:

Reconnaissance: Identify parameters in the application that are used to fetch or include files.

Input Injection: Replace file names with ../ sequences.

File Discovery: Use automated tools or manual testing to access sensitive system files like:

/etc/passwd
/etc/shadow
/proc/version
C:\Windows\win.ini
C:\boot.ini

Privilege Escalation: If sensitive credentials or config files are retrieved, further attacks (like RCE) may be possible.

Persistence: Modify config files or create backdoors if write access is achieved.

Popular Tools for Exploitation:

Burp Suite Intruder
DirBuster / DirSearch
Nikto
WFuzz
OWASP ZAP

How to Detect Directory Traversal

Detecting a directory traversal vulnerability is crucial for both red and blue teams.

Manual Detection:

Test URL and input fields with payloads like:

../etc/passwd
../../../../windows/win.ini
%2e%2e%2f

Monitor the server’s HTTP response codes:

200 OK = possible file access
403 Forbidden = restricted access
404 Not Found = file exists but not accessible

Automatic Identification:

Static Application Security Testing (SAST): Tools scan source code for insecure file handling functions like file_get_contents() in PHP or open() in Python.
Dynamic App Security Testing (Dast): Scan running apps and check the URL reactions.
Log analysis: Monitor logs for suspected file path pattern (../, %2e %2e, etc.)
SIEM Equipment: Alert Rules can mark the efforts of unusual file path access.

Risks and Real-World Impact

Potential Damage:

Exposure of system files (/etc/passwd, boot.ini)
Disclosure of application source code
Leakage of credentials/configuration
Remote Code Execution (RCE) in chained attacks
Full system compromise

High-Profile Incidents:

Fortnite (2019): A flaw in the game’s login process enabled directory traversal, which could have been used to hijack player accounts.
Microsoft IIS (2000): Unicode decoding bug allowed full server access via traversal.

Prevention of Directory Traversal

Prevention revolves around strict input validation and proper file access control.

1. Input Validation

Whitelist filenames instead of interpreting arbitrary user input.
Reject ../, %2e, and similar patterns from user inputs.
Use language-specific libraries or methods that enforce safe paths.

php

// Example in PHP

$filename = basename($_GET['file']);

python

# Example in Python

import os

if os.path.isabs(user_input) or ".." in user_input:

raise Exception("Invalid path")

2. Use of Safe APIs

Frameworks like Java’s java.nio.file.Paths.get() can be used to limit paths within a sandbox.
Use chroot or container-based sandboxes to isolate directory access.

3. Principle of Least Privilege

Ensure web applications run with limited OS-level privileges.
Sensitive directories should not be accessible to web users.

4. Web Application Firewalls (WAF)

WAFs can block suspicious path patterns automatically.
Rule-based systems like ModSecurity can help.

5. Error Handling

Avoid returning detailed error messages or stack traces.
Custom 404 pages should not reveal file system structure.

Testing for Directory Traversal

If you're developing or testing applications, you can use OWASP-recommended payloads to simulate attacks.

Sample Payloads:

../../../../etc/passwd
../../../Windows/system32/drivers/etc/hosts
%2e%2e%2f%2e%2e%2fetc%2fpasswd

Testing Frameworks:

OWASP ZAP (Zap Attack Proxy)
Burp Suite Professional
Nikto for server-level scanning
SonarQube / Checkmarx for code-level vulnerabilities

Directory Traversal in APIs and Microservices

APIs that handle file uploads, downloads, or logging are often vulnerable to traversal if not secured.

Common API Scenarios:

Log viewers
File download endpoints
Configuration preview tools

Always validate file paths and consider sandboxing file access in a separate environment.

conclusion

The directory traversal is one of the most dangerous and usually exploited web weaknesses. Its simplicity makes it attractive to the attackers, and its potential effect - especially when coupled with other weaknesses such as distance code execution - is severe.

Safety Best Practice:

Copy user inputs with allows.
Use safe API and sandbox environment.
Monitor and alert suspected path patterns.
Hard the web server and deploy WAF.

Understanding the history, detection methods and prevention strategies of the directory traversal, developers and security professionals can better defend against this silent danger.