Answer: It is not officially permitted. If members of the clergy at any level are obviously resolved to be a Freemason, they may face suspension. What we frequently encounter regarding “high-ranking” curia members being Masons is more about allegations or speculation rather than definitive evidence. Typically, hearsay does not serve as a valid foundation for dismissal or other disciplinary actions. Because Freemasonry functions as a secretive organization, confirming such claims is challenging. A person is considered innocent until proven otherwise. 

Numerous Americans find themselves confused by the restrictions on membership in the Masons. Many perceive it as an innocuous men’s organization. However, historically, the Freemasons have been staunch adversaries of the Catholic Church, holding a quasi-religious belief system that conflicts with Catholicism. Allegedly, some of their internal documents reference a strategy to diminish the power of the Catholic Church through infiltration and the introduction of an alternative “religion” that supplants doctrinal and moral values with a form of “brotherhood of man.” It represents a syncretic fusion of various religious perspectives, prioritizing merely natural virtues. The Church also forbids affiliation with Freemasonry due to the fundamental incompatibility of Masonic principles and practices with Catholic teachings. These perspectives threaten the Catholic faith, challenge the authority of the Church, and undermine the unique assertions of Jesus Christ and the Church he established. 

Evidently, no individual within the Catholic hierarchy can belong to the Freemasons. However, as you mention, “claims about senior members of the curia” being part of the organization are frequently difficult to substantiate. Thus, it is deemed “forbidden” due to the absence of evidence. We can merely wish that such accusations are untrue.