Researchers from cybersecurity firm Proofpoint claim to have discovered a new threat campaign involving malicious third-party OAuth apps that are used to infiltrate organizations\u2019 cloud environments. According to a blog on the company\u2019s website, threat actors satisfied Microsoft\u2019s requirements for third-party OAuth apps by abusing the Microsoft \u201cverified publisher\u201d status, employing brand abuse, app impersonation and other social engineering tactics to lure users into authorizing malicious apps.The potential impacts of the campaign, which Proofpoint first discovered in December 2022, include data exfiltration and mailbox abuse, the company stated. Proofpoint\u2019s analysis suggested that the campaign has targeted mainly UK-based organizations and users. The firm informed Microsoft of the malicious activity on December 20, 2022, and the campaign ended seven days later. Microsoft has since disabled the malicious applications while continuing to investigate this attack, Proofpoint confirmed.Threat actors sought to abuse OAuth privileges\u201cPublisher verified\u201d or \u201cverified publisher\u201d is a status that a Microsoft account can gain when the \u201cpublisher of the app has verified their identity using their Microsoft Partner Network (MPN) account and has associated this MPN account with their app registration,\u201d Microsoft stated. Threat actors recognize the value of verified status in the Microsoft environment to abuse OAuth privileges, increasing the probability of tricking users into granting consent when a malicious third-party OAuth app requests access to data accessible via a user\u2019s account, Proofpoint wrote.\u201cWe identified three malicious apps created by three different malicious publishers,\u201d Proofpoint stated. \u201cThese apps targeted the same organizations and are associated with the same malicious infrastructure. Multiple users were observed authorizing the malicious apps, thereby compromising their organization\u2019s environment.\u201d UK-based organizations and users were most targeted, affecting financial and marketing personnel, as well as high-profile users such as managers and executives, Proofpoint noted.Data exfiltration, mailbox, and brand abuse among campaign risksIf consent is granted by users, default delegated permissions in the malicious applications allowed threat actors to access and manipulate mailbox resources, calendar, and meeting invitations linked to compromised users\u2019 accounts, Proofpoint wrote. \u201cOffline access\u201d provided by the permissions meant that user interaction was not required after consent, while the granted token (refresh token) has a long expiry duration of over a year in most cases, giving threat actors the ability to leverage compromised accounts in subsequent BEC or other attacks, Proofpoint stated. \u201cIn addition to user accounts being compromised, impersonated organizations could suffer brand abuse.\u201dProofpoint urged businesses and users to be cautious when granting access to third-party OAuth apps, even if they are verified by Microsoft. \u201cDo not trust and rely on OAuth apps based on their verified publisher status alone. Organizations should carefully evaluate the risks and benefits of granting access to third-party apps. Further, organizations should restrict user consent to apps with verified publishers and low risk delegated permissions. Automated remediation actions, such as revoking malicious OAuth apps from your cloud environment, can greatly decrease threat actors\u2019 dwell time and prevent most post-access risks.\u201dGitHub repositories compromised by stolen OAuth tokensIn April last year, Salesforce-owned PaaS vendor Heroku and Microsoft\u2019s GitHub warned that compromised OAuth user tokens were likely used to download private data from organizations using Heroku and continuous integration and testing service Travis CI. At the time, GitHub stated that five specific OAuth applications were affected \u2013 four versions of Heroku Dashboard and Travis CI (IDs 145909, 628778, 313468, 363831, and 9261). \u201cOur analysis of other behavior by the threat actor suggests that the actors may be mining the downloaded private repository contents, to which the stolen OAuth token had access, for secrets that could be used to pivot into other infrastructure,\u201d GitHub said.