July 28, 2020 Update: Due to the complexities documented in this blog post, Microsoft is rolling out changes to e-mail forwarding configuration in Office 365. SecureSky is testing the changes that are documented at the following Microsoft URL, and will update this blog post after completion of testing to address these changes: https://docs.microsoft.com/en-us/microsoft-365/security/office-365-security/external-email-forwarding?view=o365-worldwide.
With a six times increase in COVID-19 themed incidents, security professionals need to take advantage of every possible configuration and security control to protect against this growing amount of attacks. Today we will discuss how attackers are leveraging a gap in Office 365 best practices that allows undetected eavesdropping on victim’s emails.
When attackers gain control of an account in Office 365, one of the first steps they often take is to configure email forwarding in the compromised environment. Attackers configure email forwarding in order to see new emails that arrive in the victim’s inbox – which can be responses to attacker phishing attempts sent to the victim contacts. In order to disguise their presence, the attacker does not want the victim to see those emails.