Characters allowed after colon which result in an external URL

This is an example how you can use the XSS type to fuzz URLs. It uses a base tag to get round the sandboxed iframe problems.

Created Jan 16, 2025

Updated May 27, 2025

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CategoryURL Handling

VisibilityPublic

TypeXSS

CharsetUTF-8

$[data1] placeholderhtml_entities

Code used before fuzz:

<script>window.onerror=x=>true;</script>0x0D
<base href="https://example.com" />

Template used:

<a href="https:$[chr]$[chr]example2.com" id=x></a>

Code used after fuzz:

x.protocol === 'https:' && x.host === "example2.com" && log($[i])

Sample payloads

<a href="https://example2.com" id=x></a>

<a href="https:\\example2.com" id=x></a>