Bug bounty hunter Sahad Nk recently uncovered a series of vulnerabilities that left Microsoft users’ accounts — from your Office documents to your Outlook emails — susceptible to hacking.
While working as a security researcher with cybersecurity site , Nk discovered that he was able to take over the Microsoft subdomain, , because it wasn’t properly configured. This allowed the bug hunter to set up an Azure web app that pointed to the domain’s CNAME record, which maps domain aliases and subdomains to the main domain. By doing this, Nk not only takes control of the subdomain, but also receives any and all data sent to it.
This is where the second major vulnerability comes into play.
Microsoft Office, Outlook, Store, and Sway apps send authenticated login tokens to the subdomain. When a user logs in to Microsoft Live, login.live.com, the login token would leak over to the server controlled by Nk. He would then just have to send over an email to the user asking them to click a link, which would provide Nk with a valid session token — a way to log in to the user’s account without even needing their username or password. And, because Nk has access on Microsoft’s side, that link would come in the form of a login.live.com URL, bypassing phishing detection and even the savviest of internet users.
According to , the issues were reported to Microsoft in June. They were fixed just last month, in November.