What if Chinese state-sponsored hackers have owned your OWA using several brand-new zero-day vulns? Or Eastern Europe ransomware gangs?
On March 2, Microsoft released emergency security updates to plug four security holes in Exchange Server versions 2013 through 2019 that hackers were actively using to siphon email communications from Internet-facing systems running Exchange.
The Chinese hacking group thought to be responsible has seized control over “hundreds of thousands” of Microsoft Exchange Servers worldwide, at least 30,000 in America — with each victim system representing approximately one organization that uses Exchange to process email.
The truth is, if you are running an OWA server exposed to the internet, assume you have been compromised between 02/26-03/03 and you are now in incident response mode until proven otherwise.
An adversary owning your email systems, being able to see all threads, and injecting a reply containing a malicious link into an existing thread between trusted parties is a worrying thought. You gotta train your users for events like this! And of course patch those systems immediately.
It was all over the press, but Brian Krebs covers it the best as usual, and he has a quick thing you can check to see if you are compromised:
Here is the Microsoft blog about this urgent issue, where they have an update that multiple bad actors are now attacking unpatched systems: