The weakest link is the human. Microsoft does keep the software in their Azure cloud up to date with the latest patches but still managed to lose 2.4 terabytes of data belonging to 65,000 customers in 111 countries. The reason is that someone at Microsoft misconfigured a storage container.
This story became public because a security company wanting to sell its scanning solution posted it. They also informed Microsoft, who quickly secured the container. But for every white-hat hacker scanning the internet for unsecured storage, there are ten black-hat hackers siphoning off your secrets and selling them.
By buying a high-level cloud service from a reputable vendor, you can be sure that it runs on well-patched servers without known vulnerabilities. But you’ll have no idea when your cloud vendor fails to secure some lower-level service until you read about it in the news.