Thanks for sharing. After digging in, it appears that something very similar happened here, after all. It looks like an access key with admin role leaked some time ago. At first, they just ran a quiet GetCallerIdentity, then sat on it. Then, on outage day, they leveraged it. In our case, they just did the SES thing, and tried to persist access by setting up IAM Identity Center.
These were accounts that shouldn't have had console access in the first place, and were never used by humans to log in AFAICT. I don't know exactly what they were originally for, but they were named like "foo-robots", were very old.
At first I thought maybe some previous dev had set passwords for troubleshooting, saved those passwords in a password manager, and then got owned all these years later. But that's really, really, unlikely. And the timing is so curious.
I would normally say that "That must be a coincidence", but I had a client account compromise as well. And it was very strange:
Client was a small org, and two very old IAM accounts had suddenly had recent (yesterday) console log ins and password changes.
I'm investigating the extent of the compromise, but so far it seems all they did was open a ticket to turn on SES production access and increase the daily email limit to 50k.
These were basically dormant IAM users from more than 5 years ago, and it's certainly odd timing that they'd suddenly pop on this particular day.