All real property owned or held by a city for the purposes of the Municipal Housing Law shall be exempt from levy and sale by virtue of an execution, and no execution or other judicial process shall be issued against the same nor shall any judgment against a city be a charge or lien on such real property; provided, however, that the provisions of this section shall not apply to or limit the right of obligees to pursue any remedies for the enforcement of any pledge or lien given to them on rents, fees or revenues.