The attack exploits SharePoint vulnerabilities originally disclosed at a Berlin hacking competition in May, where a Vietnamese cybersecurity researcher received a $100,000 bounty for discovering the flaws. Reuters reported that Microsoft was allegedly informed of the vulnerabilities in May but failed to fully address them in an initial July patch

And

Several cybersecurity experts compared the SharePoint campaign to the 2021 Microsoft Exchange server attacks that compromised US government systems. Former FBI Cyber Unit deputy director Cynthia Kaiser warned that hackers “already in their systems may lie dormant for extended periods before operationalizing”

Just shows in what a poor position US is now. Allies discovered it, reported it, feds didn’t prepare for it and Chinese are in. Incredible incompetence except for US allies that despite US’ isolationism still care.