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    The Spanner
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    Made by Gareth Heyes
    Follow me on Twitter: @garethheyes

    Javascript for hackers!

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    Hackvertor fuzzing tool

    By Gareth Heyes (@hackvertor)

    Published 18 years 5 months ago • Last updated March 22, 2025 • ⏱️ 2 min read

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    I've created a separate tool for HTML/JS fuzzing, I decided to do this because Hackvertor does all the hard work of conversion and I can simply extend the functionality without writing much code. The tool is already very powerful and lets you traverse unicode characters and perform whatever conversions you require and in any position in a tag. The tool features javascript logging and it's purpose is to find combinations of characters which cause javascript execution.

    How do I use it?

    The idea is you place the required code in the code window and you use placeholders like unicodeCharacter which is the current unicode character. charNum contains the unicode character number, input stores the original data before conversion, output shows the the code which triggered the javascript execution (if any). The input box "Uni Character position" tells the fuzzer were to start the character from and the "Code to generate" specifies the amount of code that the fuzzer should run through.

    This is powerful because you can now automate the process of logging with the "logFuzz" callback and combine it with Hackvertor's conversion tags, so you can traverse unicode characters and convert each one in turn to hex entities, octal and urlencode etc. It currently only works on Firefox because it uses the base64 encode/decode native functions but I may expand it in future to allow other browsers.

    Update...

    The tool now accepts unicode characters higher than 256. Big thanks to David (AKA Thornmaker) who suggested using a Hackvertor tag rather than the raw unicode string, excellent suggestion! :D I've removed the output placeholder because of problems with unicode characters in String.Replace, you can still get the input string though which can be used in the main Hackvertor tool to get the raw output.

    Check it out here:- Hackvertor fuzzing tool

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