FireEye is reporting the current known tactics that the SVR used to compromise Microsoft 365 cloud data as part of its SolarWinds operation:

Mandiant has observed UNC2452 and other threat actors moving laterally to the Microsoft 365 cloud using a combination of four primary techniques:

• Steal the Active Directory Federation Services (AD FS) token-signing certificate and use it to forge tokens for arbitrary users (sometimes described as Golden SAML ). This would allow the attacker to authenticate into a federated resource provider (such as Microsoft 365) as any user, without the need for that user’s password or their corresponding multi-factor authentication (MFA) mechanism.
• Modify or add trusted domains in Azure AD to add a new federated Identity Provider (IdP) that the attacker controls. This would allow the attacker to forge tokens for arbitrary users and has been described as an Azure AD backdoor .
• Compromise the credentials of on-premises user accounts that are synchronized to Microsoft 365 that have high privileged directory roles, such as Global Administrator or Application Administrator.
• Backdoor an existing Microsoft 365 application by adding a new application or service principal credential in order to use the legitimate permissions assigned to the application, such as the ability to read email, send email as an arbitrary user, access user calendars, etc.

Lots of details here , including information on remediation and hardening.

The more we learn about the this operation, the more sophisticated it becomes.

In related news, MalwareBytes was also targeted .