HTTP Dir Traversal

ALTERNATIVE NAMES

Directory Traversal, Path Traversal, dot-dot-slash, directory climbing or backtracking.

AFFECTED SYSTEMS

Systems with insecure permissions or poor coding

SEVERITY

High

BACKGROUND

Dir traversal Attack aims to access files and folders that are available on the server as a result of poor server-side coding and/or security measures. When scripting languages first developed, no one realized files stored outside the document folder will be readable because of poor coding.

DESCRIPTION

Directory Traversal mostly handled with manual intervention. An attacker must try filenames and paths on server-side scripts if the script is offering a usage similar to this one:

http://site.com/get-file?f=main.php

And the attacker may try a GET URL like this:

http://site.com/get-template?f=../../../etc/passwd

Suppose that get-file is used to view the file called by f= variable, one can try to view the files that are beyond the document folder.

ANALYSIS

Attackers will check for arbitrary file requests that can be made by GET or POST. Manually trying for several locations, it will not take more than 10 tries to reveal or view files located on the server.

SOLUTION

There is no exact solution to this kind of attack but it is always better to harden servers for such kind of attacks. This steps below should be checked to prevent data leaks:

Be sure that you can’t access the files beyond document root, try to view the files such as /etc/passwd or c:\Windows\win.ini by hardcoding them on a script under the public folder with the specific user privileges
Apply latest patches for the system and applications. Older versions of scripting languages known to allow path traversal
Use GET and POST filtering functions provided by the scripting language such as realpath() function offered by PHP.
Disable unused shell command functions on the script interpreter such as PHP disable_functions directive.
Restrict access to compilers from web user.
Remove unused user privileges and user groups from web user.
Make sure web user doesn’t have execute privileges on publicly writable folders.
Use WAF

LEGAL

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