The vulnerability lies in the 'com.liferay.product.navigation.control.menu.web.internal.PortletBackLinkProductNavigationControlMenuEntry' class, specifically within the 'getLabel' method. The provided patch '30d07ef9c95c66828818a4ba577ff56f8e2dd0d3' clearly shows that the 'urlBackTitle' variable, taken from a request parameter, was being used to format a string for display without any sanitization. This allows an attacker to inject arbitrary HTML or script content via the 'com_liferay_layout_admin_web_portlet_GroupPagesPortlet_backURLTitle' parameter, leading to a reflected XSS attack. The fix involves wrapping the 'urlBackTitle' with 'HtmlUtil.escape()' to neutralize any malicious input before it is rendered on the page. Therefore, the 'getLabel' function is the direct location of the vulnerability.