The US agency responsible for maintaining and designing the nation’s cache of nuclear weapons was among those breached by a hack of Microsoft Corp.’s SharePoint document management software, according to a person with knowledge of the matter.

Microsoft has patched two critical zero-day SharePoint security flaws that have already been exploited by hackers to attack vulnerable organizations.

Bloomberg reported that no sensitive or classified information is known to have been compromised in the attack on the National Nuclear Security Administration, the agency responsible for maintaining ...