FirstBlood-#93XSS using ref Parameter

On 2021-05-10, mava reported:

Hi zseano, I found a reflected XSS inside Firstblood.


  1. Visit:,(document.domain)//


This vulnerability allows an attacker to execute arbitrary Javascript code.


The parameter must be sanitized correctly.

Best regards,

P3 Medium

Endpoint: /register.php

Parameter: ref

Payload: 1%27AutoFocus/ContentEditable/OnFocusIn=_=confirm,_(1)//

FirstBlood ID: 4
Vulnerability Type: Reflective XSS

The parameter "ref" is vulnerable to XSS on register.php. The developer made use of htmlentities but this is inadequate as the HREF is wrapped in single quotes.

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Creator & Administrator

Nice find ! :)

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