This article will explore the mechanism behind this attack, how to identify it, why /etc/passwd is the target, and, most importantly, how to defend against it. 1. What is Path Traversal?
The general format is:
Similar bypasses include:
Path traversal occurs when an application accepts user input containing file paths without proper sanitization.
This specific pattern is used by attackers to exploit web applications that don't properly check user input, allowing them to escape the intended website directory and read sensitive system files—most commonly the /etc/passwd file on Linux. 1. Anatomy of the Payload -page-....-2F-2F....-2F-2F....-2F-2Fetc-2Fpasswd
Imagine a web application that loads page content based on a page parameter:
This public link is valid for 7 days and shares a thread, including any personal information you added. This link or copies made by others cannot be deleted. If you share with third parties, their policies apply. Can’t copy the link right now. Try again later.
Do not try to filter out dangerous characters (like .. ). Instead, validate that the input matches an expected pattern.
If an allowlist is not possible, ensure user input only contains alphanumeric characters. Reject inputs containing dots ( . ), slashes ( / ), or encoded equivalents like %2F . Use built-in path sanitization functions like basename() in PHP, which strips out directory paths and only returns the file name. 3. Use Proper Server Access Controls This article will explore the mechanism behind this
In many web application attacks, successfully retrieving /etc/passwd is the “proof of concept” that confirms a path traversal vulnerability exists.
: While /etc/passwd must be readable by all users (to allow ls -l to display owner names), access to /etc/shadow is restricted to root. This ensures that sensitive information like encrypted passwords is protected.
What or framework your application uses
Stay vigilant. Secure your file operations. And the next time you see a string like -page-....-2F-2Fetc-2Fpasswd , you’ll know exactly what it means – and how to stop it cold. The general format is: Similar bypasses include: Path
Attackers use sequences like ../ to move up directories and access files outside the web root.
: A more procedural guide that explains how to identify and remediate these flaws in real-world applications.
This is the URL-encoded version of a forward slash / . Sometimes, developers filter simple / characters, so attackers use encoding to bypass those filters.
The /etc/passwd file is a critical text file in Unix-like operating systems, including Linux. It contains a list of all registered users on the system. For each user, the file provides a line with a specific format that includes: