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To get successful access to those cloud environments, the attackers have deployed credential stuffing attacks: They attempted to reuse valid credentials they obtained from other services or applications. Once all these steps were done, the attackers could easily access the malicious application, even in the case of a password change from the compromised administrator account.

Microsoft on Thursday warned of a consumer-facing attack that made use of rogue OAuth applications on compromised cloud tenants to ultimately seize control of Exchange servers and spread spam. The unauthorized access to the cloud tenant permitted the adversary to register a malicious OAuth application and grant it elevated permissions, and eventually modify Exchange Server settings to allow inbound emails from specific IP addresses to be routed through the compromised email server.

Microsoft says a threat actor gained access to cloud tenants hosting Microsoft Exchange servers in credential stuffing attacks, with the end goal of deploying malicious OAuth applications and sending phishing emails. "The unauthorized access to the cloud tenant enabled the actor to create a malicious OAuth application that added a malicious inbound connector in the email server."

In this Help Net Security video, Security Consultant Kam Talebzadeh and Senior Security Researcher Nevada Romsdahl from Secureworks, showcase SquarePhish, a tool that combines QR codes and OAuth 2.0 device code flow for advanced phishing attacks. If you're at Black Hat USA 2022, you can learn more about SquarePhish.

Cloud-based repository hosting service GitHub on Friday shared additional details into the theft of GitHub integration OAuth tokens last month, noting that the attacker was able to access internal NPM data and its customer information. "Using stolen OAuth user tokens originating from two third-party integrators, Heroku and Travis CI, the attacker was able to escalate access to NPM infrastructure," Greg Ose said, adding the attacker then managed to obtain a number of files -.

Google last month addressed a high-severity flaw in its OAuth client library for Java that could be abused by a malicious actor with a compromised token to deploy arbitrary payloads. Tracked as CVE-2021-22573, the vulnerability is rated 8.7 out of 10 for severity and relates to an authentication bypass in the library that stems from an improper verification of the cryptographic signature.

Salesforce-owned subsidiary Heroku on Thursday acknowledged that the theft of GitHub integration OAuth tokens further involved unauthorized access to an internal customer database. As a consequence, Salesforce said it's resetting all Heroku user passwords and ensuring that potentially affected credentials are refreshed.

Cloud-based code hosting platform GitHub described the recent attack campaign involving the abuse of OAuth access tokens issued to Heroku and Travis-CI as "Highly targeted" in nature. "This pattern of behavior suggests the attacker was only listing organizations in order to identify accounts to selectively target for listing and downloading private repositories," GitHub's Mike Hanley said in an updated post.

GitHub revealed details tied to last week's incident where hackers, using stolen OAuth tokens, downloaded data from private repositories. "We do not believe the attacker obtained these tokens via a compromise of GitHub or its systems because the tokens in question are not stored by GitHub in their original, usable formats," said Mike Hanley, chief security officer, GitHub.

GitHub has shared a timeline of this month's security breach when a threat actor gained access to and stole private repositories belonging to dozens of organizations. The attacker used stolen OAuth app tokens issued to Heroku and Travis-CI to breach GitHub.com customer accounts with authorized Heroku or Travis CI OAuth app integrations.