The 'name' param in jira-components/jira-webapp/src/main/webapp/secure/admin/user/views/deleteuserconfirm.jsp is not sanitised, enabling arbitrary html/script execution.
A url to demonstrate this issue is: http://localhost:8080/secure/admin/user/DeleteUser!default.jspa?name=a"><script>alert(document.cookie);</script>&returnUrl=UserBrowser.jspa