💣 SXSS in the user profile via the timezone displayer (xwiki xwiki-platform)

Description

XWiki Platform is a generic wiki platform offering runtime services for applications built on top of it. Any registered user can exploit a stored XSS through their user profile by setting the payload as the value of the time zone user preference. Even though the time zone is selected from a drop down (no free text value) it can still be set from JavaScript (using the browser developer tools) or by calling the save URL on the user profile with the right query string. Once the time zone is set it is displayed without escaping which means the payload gets executed for any user that visits the malicious user profile, allowing the attacker to steal information and even gain more access rights (escalation to programming rights). This issue is present since version 4.1M2 when the time zone user preference was introduced. The issue has been fixed in XWiki 14.10.5 and 15.1RC1.