Common Password Patents has an excellent overview of patents dealing with checking for weak passwords. As the summary notes there are multiple patents covering every single aspect of password management, authentication, recovery – anything you can think of to do with passwords. The posted list of weak/common password checking alone is startling:

Although as noted some/most of these patents may have been obtained defensively with the state of patent trolling at the moment it would not be surprising if some form of assertion with accompanying litigation eventually appears.