Unknown threat actors have breached the National Nuclear Security Administration's network in attacks exploiting a recently patched Microsoft SharePoint zero-day vulnerability chain. NNSA is a semi-autonomous U.S. government agency part of the Department of Energy that maintains the country's nuclear weapons stockpile and is also tasked with responding to nuclear and radiological emergencies within the United States and abroad. A Department of Energy spokesperson confirmed in a statement that hackers gained access to NNSA networks last week. "On Friday, July 18th, the exploitation of a Microsoft SharePoint zero-day vulnerability began affecting the Department of Energy, including the NNSA," Department of Energy Press Secretary Ben Dietderich told BleepingComputer. "The Department was…