Cybersecurity researchers have disclosed a Microsoft 365 campaign that has been observed leveraging an adversary-in-the-middle (AitM) relay to capture sign-in sessions and then replay the stolen tokens to break into email accounts at 79 organizations.

Huntress, which observed the activity between July 14 and September 22, 2026, said it detected 497 successful Microsoft 365 sign-in events across the victim organizations from over 200,000 login attempts, with the attackers ultimately compromising 97 accounts and registering 48 rogue Entra devices.

"Rather than guessing passwords, the attacker replayed sign-in tokens stolen from victims, and we've traced more than 200,000 failed login attempts from the campaign window back to the 193.26.115[.]0/24 IP range," Huntress researchers Andrea Hatcher, Susannah Matt, Matt Poto, and Andrew Schwartz said.

The attack has been found to employ an AitM login page, which sits between the victims and legitimate Microsoft infrastructure to capture the entered credentials and MFA codes and relay the information to the real login page.

The end goal is to collect the access token issued by Microsoft following the sign-in process so that it doesn't have to bypass MFA a second time. The "proof of login" token is subsequently replayed by the attacker from their own devices within minutes to conduct automated sign-in attempts against Microsoft 365 services.

The approach has been codenamed token spraying, as it involves the attacker replaying many stolen tokens at scale across several organizations in a manner that's analogous to password spraying.

Upon gaining successful access, the attackers moved to add their own authenticator app as a form of persistence to complete MFA challenges for new sign-ins and overcome scenarios where the stolen session token expires or gets revoked by the victim.

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