Just recently, an attack believed to be perpetrated by the Chinese hacker group Storm-0558 targeted several government agencies. They used fake digital authentication tokens to access webmail accounts running on Microsoft’s Outlook service. In this incident, the attackers stole a signing key from Microsoft, enabling them to issue functional access tokens for Outlook Web Access (OWA) and Outlook.com and to download emails and attachments. Due to a plausibility check error, the digital signature, which was only intended for private customer accounts (MSA), also worked in the Azure Active Directory for business customers.