Cybercriminals are building phishing pages that exist only inside victims’ browsers

Barracuda details a DocuSign-themed phishing campaign that renders login pages locally via blob URLs, abusing genuine Microsoft OAuth and Teams infrastructure.

Barracuda researchers describe a phishing campaign that starts with DocuSign-themed emails carrying calendar invites pointing to genuine Microsoft OAuth endpoints, then routes victims through Microsoft Teams to a resource hosted on cdn.bloom[.]io. The login page is assembled entirely inside the victim's browser from a blob URL, registers a service worker, and runs inside a sandboxed iframe that receives live instructions from the attacker's backend. Hidden command-and-control configuration indicates the page is part of a centrally managed phishing platform that can be updated and steered across many victims. Barracuda recommends phishing-resistant MFA such as FIDO2 keys or passkeys, monitoring of OAuth flows and redirect chains, and behavior-based identity controls rather than URL blocklisting.