User login widget breaks homepage

I create a page to be used as frontpage, giving it the path /front. Then I add the "User login" widget to any region. The page will be broken for the anonymous user, showing "server error" in the browser.

Steps:
1) Create a page and assign it as a home page
2) Add "User login" widget
3) Open the home page as an anonymous user. You will not be able to see the website.