Generic HTML Sanitizer Bypass Investigation

2023-07-03

[public] 19.6K views, 6.55K likes, dislikes audio only

I stumbled over a weird HTML behavior on Twitter and started to investigate it. Did I just stumble over a generic HTML Sanitizer bypass?

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The Tweet: https://twitter.com/MRCodedBrain/status/1662701541680136195

Google XSS: /youtube/video/lG7U3fuNw3A

HTML Spec: https://html.spec.whatwg.org/multipage/parsing.html#parse-error-invalid-first-character-of-tag-name

Chapters:

00:00 - Intro

01:09 - Sanitizing vs. Encoding

02:32 - Developing HTML Sanitizer Bypass

05:03 - Attacking DOMPurify

07:08 - Attacking Server-side Sanitizer

08:31 - HTML Parse Error Specification

10:08 - Potential Impact

11:55 - hextree.io

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