AntiXSS - Library

"Cross-site scripting (XSS) is a type of computer security vulnerability typically found in Web applications. XSS enables attackers to inject client-side script into Web pages viewed by other users. A cross-site scripting vulnerability may be used by attackers to bypass access controls such as the same origin policy. Cross-site scripting carried out on websites accounted for roughly 84% of all security vulnerabilities documented by Symantec as of 2007." - http://en.wikipedia.org/wiki/Cross-site_scripting

DEMO:

http://anti-xss-demo.suckup.de/

NOTES:

1. Use filter_input() - don't use GLOBAL-Array (e.g. $_SESSION, $_GET, $_POST, $_SERVER) directly

2. Use HTML Purifier if you need a more configurable solution

3. Add "Content Security Policy's" -> Introduction to Content Security Policy

4. DO NOT WRITE YOUR OWN REGEX TO PARSE HTML!

5. READ THIS TEXT -> XSS (Cross Site Scripting) Prevention Cheat Sheet

6. TEST THIS TOOL -> Zed Attack Proxy (ZAP)

Install via "composer require"

composer require voku/anti-xss

Usage:

$antiXss = new AntiXSS();

Example 1: (HTML Character)

$harm_string = "Hello, i try to <script>alert('Hack');</script> your site";
$harmless_string = $antiXss->xss_clean($harm_string);

// Hello, i try to alert&#40;'Hack'&#41;; your site

Example 2: (Hexadecimal HTML Character)

$harm_string = "<IMG SRC=&#x6A&#x61&#x76&#x61&#x73&#x63&#x72&#x69&#x70&#x74&#x3A&#x61&#x6C&#x65&#x72&#x74&#x28&#x27&#x58&#x53&#x53&#x27&#x29>";
$harmless_string = $antiXss->xss_clean($harm_string);
    
// <IMG >

Example 3: (Unicode Hex Character)

$harm_string = "<a href='&#x2000;javascript:alert(1)'>CLICK</a>";
$harmless_string = $antiXss->xss_clean($harm_string);
    
// <a >CLICK</a>

Example 4: (Unicode Character)

$harm_string = "<a href=\"\u0001java\u0003script:alert(1)\">CLICK<a>";
$harmless_string = $antiXss->xss_clean($harm_string);
    
// <a >CLICK</a>

Example 5.1: (non Inline CSS)

$harm_string = '<li style="list-style-image: url(javascript:alert(0))">';
$harmless_string = $this->security->xss_clean($harm_string);

// <li >

Example 5.2: (with Inline CSS)

$harm_string = '<li style="list-style-image: url(javascript:alert(0))">';
$antiXss->removeEvilAttributes(array('style')); // allow style-attributes
$harmless_string = $antiXss->xss_clean($harm_string);

// <li style="list-style-image: url(alert&#40;0&#41;)">

Example 6: (check if an string contains a XSS attack)

$harm_string = "\x3cscript src=http://www.example.com/malicious-code.js\x3e\x3c/script\x3e";
$harmless_string = $antiXss->xss_clean($harm_string);

// 

$antiXss->isXssFound(); 

// true

Unit Test:

1. Composer is a prerequisite for running the tests.

composer install

2. The tests can be executed by running this command from the root directory:

./vendor/bin/phpunit