An anonymous reader shared this report from Bloomberg:
China-linked hackers breached the corporate account of a Microsoft engineer and are suspected of using that access to steal a valuable key that enabled the hack of senior U.S. officials’ email accounts, the company said in a blog post. The hackers used the key to forge authentication tokens to access email accounts on Microsoft’s cloud servers, including those belonging to Commerce Secretary Gina Raimondo, Representative Don Bacon and State Department officials earlier this year.
The U.S. Cybersecurity and Infrastructure Security Agency and Microsoft disclosed the breach in June, but it was still unclear at the time exactly how hackers were able to steal the key that allowed them to access the email accounts. Microsoft said the key had been improperly stored within a “crash dump,” which is data stored after a computer or application unexpectedly crashes…
The incident has brought fresh scrutiny to Microsoft’s cybersecurity practices.
Microsoft’s blog post says they corrected two conditions which allowed this to occur. First, “a race condition allowed the key to be present in the crash dump,” and second, “the key material’s presence in the crash dump was not detected by our systems.”
We found that this crash dump, believed at the time not to contain key material, was subsequently moved from the isolated production network into our debugging environment on the internet connected corporate network. This is consistent with our standard debugging processes. Our credential scanning methods did not detect its presence (this issue has been corrected).
After April 2021, when the key was leaked to the corporate environment in the crash dump, the Storm-0558 actor was able to successfully compromise a Microsoft engineer’s corporate account. This account had access to the debugging environment containing the crash dump which incorrectly contained the key. Due to log retention policies, we don’t have logs with specific evidence of this exfiltration by this actor, but this was the most probable mechanism by which the actor acquired the key.