The introduction text on a Personal Campaign Page (PCP) was not properly sanitised prior to display on the Personal Campaign page.
Cross Site Scripting
CiviCRM versions 5.35.0 and earlier
CiviCRM version 5.35.1 and ESR version 5.33.3
Upgrade to the latest version of CiviCRM
Seamus Lee of JMA Consulting and CiviCRM Core Team for reporting and fixing the issue.