Hackers Abused Microsoft’s Verified Publisher OAuth Apps to Breach Corporate Email Accounts

Microsoft on Tuesday said it took steps to disable fake Microsoft Partner Network accounts that were used for creating malicious OAuth applications as part of a malicious campaign designed to breach organizations’ cloud environments and steal email.

On top of that, Microsoft said it implemented additional security measures to improve the vetting process associated with the Microsoft Cloud Partner Program and minimize the potential for fraud in the future.

“The actor used fraudulent partner accounts to add a verified publisher to OAuth app registrations they created in Azure AD,” the company explained.

It also said that unlike a previous campaign that compromised existing Microsoft verified publishers to take advantage of OAuth app privileges, the latest attacks are designed to impersonate legitimate publishers to become verified and distribute the rogue apps.

The campaign is said to have come to an end on December 27, 2022, after Proofpoint informed Microsoft of the attack on December 20 and the apps were disabled.

Then in September 2022, Microsoft revealed that it dismantled an attack that made use of rogue OAuth applications deployed on compromised cloud tenants to ultimately seize control of Exchange servers and distribute spam.

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