Microsoft has warned of an active phishing campaign targeting Office 365 users with a "crafty combination" of techniques aimed at bypassing email filters.
The attack uses legitimate-looking original sender email addresses, spoofed display sender addresses that contain target usernames and domains, and display names that mimic legitimate services to slip past defenses, Microsoft Security Intelligence wrote in a Twitter thread.
Emails' original sender addresses have variations of the word "referral" and use different top-level domains, officials note. The emails themselves have a SharePoint lure in both the display name and email message, which is disguised as a file share request for "Staff Reports," "Bonuses," "Pricebooks," or other documents, with a link that redirects victims to the phishing page.
The malicious emails have two URLs with malformed HTTP headers. One, the primary phishing URL, is a Google storage resource that redirects the victim to an AppSpot domain, which requires them to log in before presenting them with another Google User Content domain that has an Office 365 phishing page. A second URL, located in the notification settings, redirects to a compromised SharePoint site, which Microsoft says adds legitimacy to this campaign.
"Both URLs require sign-in to continue to the final page, bypassing many sandboxes," officials write.
Read Microsoft Security Intelligence's full thread for more details.