Our investigation of the security incident disclosed by Microsoft and CISA and attributed to Chinese threat actor Storm-0558, found that this incident seems to have a broader scope than originally assumed. Organizations using Microsoft and Azure services should take steps to assess potential impact.
Fantastic writeup. I wonder, how does a threat actor get access to a signing key like this? There was no mention of how the key got leaked in the first place.
Below is a more detailed report about the IOCs, but indeed, they don’t seem to want to say anything about the original source of the key leak.
https://www.microsoft.com/en-us/security/blog/2023/07/14/analysis-of-storm-0558-techniques-for-unauthorized-email-access/
Yes, that part is still undisclosed by Microsoft. It is mentioned in the article as well:
We will continue to closely monitor this incident and provide updates; this is still an ongoing investigation and there are many unanswered questions (how did the threat actor acquire the key? When exactly did it happen? Were other keys compromised as well?).
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