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PHP function to sanitize input prevent XSS

Important Ibis answered on April 12, 2024 Popularity 1/10 Helpfulness 1/10

answer PHP function to sanitize input prevent XSS

PHP function to sanitize input prevent XSS

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<?php
// Function Description:

// The _E function is designed to sanitize input strings by removing 
// potentially dangerous script tags and JavaScript executions. 
// This ensures that the input data does not contain any malicious code 
// that can be executed on the client side, which is crucial for preventing 
// Cross-Site Scripting (XSS) attacks.

// How the Function Works:

// Regex Pattern Definition:
// The function defines a regular expression pattern that identifies <script> 
// tags and any usage of the javascript: protocol within strings. The pattern used 
// is /<script.*?>.*?<\/script>|javascript:[^\'"]*/i, which captures:

// Any content enclosed within <script> and </script> tags, including nested and 
// malformed tags.
// Any instance of the javascript: protocol, which is often used to execute JavaScript 
// code directly from HTML attributes like onclick, href, etc.

// Removing Dangerous Content:
// The function uses PHP's preg_replace function to search the input string for 
// matches to the regex pattern and replace them with an empty string (''). 
// This effectively removes dangerous script elements and JavaScript code from the input.

// Comparison and Conditional Encoding:
// After cleaning, the function compares the original input string with the cleaned 
// version. If any dangerous content was found and removed (i.e., if the cleaned string 
// differs from the original), the function further sanitizes the cleaned string by 
// escaping HTML entities. This is done using the htmlentities function with the flags 
// ENT_QUOTES | ENT_IGNORE, in "UTF-8" character encoding to prevent any remaining 
// special characters from being executed as HTML or JavaScript.

// Returning the Result:

// If dangerous content was removed, the function returns the sanitized and escaped 
// string to ensure safety.
// If no dangerous content was found (i.e., the cleaned string is the same as the 
// original), the function returns the original string as is, preserving the input 
// data without any changes.
// Usage Context:
// This function is particularly useful in environments where user-generated input is 
// displayed back on web pages. It helps in maintaining the integrity of the data while 
// ensuring that it is safe for display without risk of XSS attacks.

// PHP Code Example:

function _E($ts): string {
    // Define the pattern to remove dangerous script tags and JavaScript usage
    $pattern = '/<script.*?>.*?<\/script>|javascript:[^\'"]*/i';
    // Remove dangerous parts from the string
    $cleaned = preg_replace($pattern, '', $ts);

    // Check if modifications were made to the original string
    if ($cleaned !== $ts) {
        // Encode for safety if dangerous elements were removed
        return htmlentities($cleaned, ENT_QUOTES | ENT_IGNORE, "UTF-8");
    }

    // Return the original text if no dangerous elements were found
    return $ts;
}


// This function highlights a practical approach to mitigating one of the 
// common web security vulnerabilities by carefully examining and sanitizing 
// user inputs.

// Usage:

$clean_text = _E($_POST['some-field']);
// or 
$clean_text = _E($_GET['some-field']);

Popularity 1/10 Helpfulness 1/10 Language php

Source: Grepper

Tags: function input php sanitize xss

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Contributed on Apr 12 2024

Important Ibis

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PHP function to sanitize input prevent XSS

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