This attack aims to access files and directories that are stored outside web root folder. By browsing the application, one should look for absolute links to files stored on the web server and how this is done. By manipulating variables that reference files with “dot-dot-slash (../)” sequences and its variations it’s 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 idea is to use “../” sequences to move up to root directory, thus permitting to navigate thru file system.
This attack can be execute with a external malicious code injected on the path, the way of the Resource Injection attack, but it’s a Path Traversal attack
This attack is also named of “dot-dot-slash”, “directory traversal”, “directory climbing” and “backtracking”.
To perform this attack it’s not necessary to use a specific tool, but it’s recommended to use a spider/crawler to detect all URLs available.
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.
Unicode/UTF-8 Encoding (only for systems support UTF-8 sequences)
..%c0%af represents ../ ..%c1%9c represents ..\
Root directory: “ / “ Directory separator: “ / “
Root directory: “ <partition letter> : \ “ Directory separator: “ / “ or “ \ ”
Likelihood of exploitation
In order to identify the possibility to execute this attack, it’s needed to observe how the application deals with the resources in use. The following examples show some situations.
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. Ex:
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:
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 all disc.
It's also possible to include files, and scripts, located on external website,
These examples illustrate a case when an attacker make the server show the CGI source code;
This example was extracted from: Wikipedia - Directory Traversal
A typical example of vulnerable application code is:
<?php $template = 'blue.php'; if ( is_set( $_COOKIE['TEMPLATE'] ) ) $template = $_COOKIE['TEMPLATE']; include ( "/home/users/phpguru/templates/" . $template ); ?>
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
UNIX etc/passwd is a common file used to demonstrate directory traversal, as it is often used by crackers to try cracking the passwords.