XSS Bypass

Introduction

For those new to Cross-Site Scripting (XSS) attacks, it is essential to first understand the fundamental concepts before exploring filter bypass techniques.

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Alternatives to alert()

Many web applications block the alert() function to mitigate XSS attacks. Below are alternative functions that can be used:

• confirm() instead of alert()

• prompt() instead of alert()

• console.log() instead of alert()

• eval() instead of alert()

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Alternatives to the onerror Event Handler

If the onerror event handler is blocked, the following alternatives can be used to trigger JavaScript execution:

• onload

• onfocus

• onmouseover

• onblur

• onclick

• onscroll

These event handlers can be embedded within HTML elements to execute scripts when the event is triggered.

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Handling Parentheses Filtering

If parentheses () are filtered, backticks ` ` can be used as an alternative. Examples:

<script>alert`1`</script>
<img src=x onerror=alert`1`>
<img src=x onerror=prompt`1`>
javascript:prompt`1`
javascript:alert`1`

This method is effective against weak input sanitization mechanisms that only block standard function calls enclosed in parentheses.

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Additional Resources

For further learning and reference, the following resources provide comprehensive details on XSS filter evasion techniques:

1. PortSwigger XSS Cheat Sheet - Visit PortSwigger
2. OWASP XSS Filter Evasion Cheat Sheet - Visit OWASP

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Contact Information

For discussions and insights, you can connect with:

• @Fani Malik

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Enhanced and reformatted for HowToHunt repository by remonsec