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CISA report on the Storm-0558 2023 intrusion into Microsoft Exchange Online

Jesus this is rough!

In May and June 2023, a threat actor compromised the Microsoft Exchange Online mailboxes of 22 organizations and over 500 individuals around the world. The actor—known as Storm-0558 and assessed to be affiliated with the People’s Republic of China in pursuit of espionage objectives—accessed the accounts using authentication tokens that were signed by a key Microsoft had created in 2016. This intrusion compromised senior United States government representatives working on national security matters, including the email accounts of Commerce Secretary Gina Raimondo, United States Ambassador to the People’s Republic of China R. Nicholas Burns, and Congressman Don Bacon. Signing keys, used for secure authentication into remote systems, are the cryptographic equivalent of crown jewels for any cloud service provider. As occurred in the course of this incident, an adversary in possession of a valid signing key can grant itself permission to access any information or systems within that key’s domain. A single key’s reach can be enormous, and in this case the stolen key had extraordinary power. In fact, when combined with another flaw in Microsoft’s authentication system, the key permitted Storm-0558 to gain full access to essentially any Exchange Online account anywhere in the world. As of the date of this report, Microsoft does not know how or when Storm-0558 obtained the signing key. […] The Board finds that this intrusion was preventable and should never have occurred. The Board also concludes that Microsoft’s security culture was inadequate and requires an overhaul, particularly in light of the company’s centrality in the technology ecosystem and the level of trust customers place in the company to protect their data and operations. The Board reaches this conclusion based on: 1. the cascade of Microsoft’s avoidable errors that allowed this intrusion to succeed; 2. Microsoft’s failure to detect the compromise of its cryptographic crown jewels on its own, relying instead on a customer to reach out to identify anomalies the customer had observed; 3. the Board’s assessment of security practices at other cloud service providers, which maintained security controls that Microsoft did not; 4. Microsoft’s failure to detect a compromise of an employee’s laptop from a recently acquired company prior to allowing it to connect to Microsoft’s corporate network in 2021; 5. Microsoft’s decision not to correct, in a timely manner, its inaccurate public statements about this incident, including a corporate statement that Microsoft believed it had determined the likely root cause of the intrusion when in fact, it still has not; even though Microsoft acknowledged to the Board in November 2023 that its September 6, 2023 blog post about the root cause was inaccurate, it did not update that post until March 12, 2024, as the Board was concluding its review and only after the Board’s repeated questioning about Microsoft’s plans to issue a correction; 6. the Board’s observation of a separate incident, disclosed by Microsoft in January 2024, the investigation of which was not in the purview of the Board’s review, which revealed a compromise that allowed a different nation-state actor to access highly-sensitive Microsoft corporate email accounts, source code repositories, and internal systems; and 7. how Microsoft’s ubiquitous and critical products, which underpin essential services that support national security, the foundations of our economy, and public health and safety, require the company to demonstrate the highest standards of security, accountability, and transparency. Throughout this review, the Board identified a series of Microsoft operational and strategic decisions that collectively point to a corporate culture that deprioritized both enterprise security investments and rigorous risk management.

(tags: cisa reports security infosec microsoft exchange china storm-0558 hacking incidents)