WCM tip #21: Content Search Web Part publishes the internal URLs of catalog content
When building content aggregations for catalog content in cross-site publishing scenarios Content Search Web Part includes the original URL of the catalog item in the page source.
Content Search Web Part uses by default JavaScript-based Display Template for rendering content aggregations. Since JavaScript is client-side technology executed in the web browser, Content Search Web Part renders in the page source raw data that it retrieved from SharePoint 2013 Search and which is then rendered using Display Templates. Although not visible on the screen, when examining page source you can find the original URL of each catalog item. Depending on where the content is stored that might reveal internal URLs that you are using. One way of preventing the raw data to be included in page’s source is to use server-side rendering instead and process the data before it is sent to the browser.