OAuth Vulnerabilities in Entra ID Could Exploit ChatGPT to Breach User Email Accounts

Cybersecurity: OAuth Consent Vulnerabilities in Microsoft Entra ID

Recent analyses have identified that OAuth consent attacks within Microsoft Entra ID can provide unauthorized access to cloud email systems. This vulnerability allows threat actors to exploit trusted applications, such as ChatGPT, if permissions are misused.

In a potential scenario, a user within an Entra ID tenant might inadvertently grant Microsoft Graph OAuth permissions to a legitimate service principal like ChatGPT. These permissions can include Mail.Read , offline_access , profile , and openid . The primary risk arises when users are deceived into approving a consent screen, thereby allowing persistent API access to their mailbox without their explicit awareness.

The Entra AuditLogs reveal two critical events linked by a common CorrelationId: the addition of a service principal and the granting of consent to an application. Such actions indicate that an application, identified by its unique AppId and AppOwnerOrganizationId, has been integrated into the tenant and granted permissions like Mail.Read for a specific user principal.

These consents are typically non-admin, aligning with common OAuth phishing techniques that target regular users to circumvent stricter administrative controls. Once access is granted, attackers can exploit the application's token to read messages, gather sensitive data, and engage in conversation hijacking or business email compromise (BEC) scenarios.

Detection efforts should focus on the "who, what, when, where, how" questions driven by content Audit Logs . Investigators should verify the legitimacy of consent actions, the sanctioned status of applications, and the alignment of requested scopes with organizational policies.

High-value analytics include alerting on non-admin consents for new third-party applications requesting risky scopes such as Mail.Read or Files.Read . This process involves correlating consent and service principal events by CorrelationId, verifying mismatches in AppOwnerOrganizationId, and checking that ConsentContext.IsAdminConsent is set to False.

Further enrichment with publisher reputation and application prevalence data assists in distinguishing benign high-use SaaS from potentially adversary-controlled registrations. Parsing ConsentAction.Permissions strings can provide crucial information for triage and response efforts, especially when scopes include permissions like Mail.Read or offline_access on unfamiliar applications.

When an OAuth grant is identified as malicious or unsanctioned, immediate revocation of the specific oAuth2PermissionGrant and removal of the associated service principal from the tenant are essential steps. This action revokes the attacker's token-based access without altering user credentials.

In the long term, organizations should enhance Entra user consent settings to mitigate potential attack avenues. Continuous monitoring for risky OAuth applications in Defender for Cloud Apps and focused investigations into suspicious consent patterns are recommended. Microsoft provides options to disable user consent entirely, restrict consent to verified publishers, or adopt managed consent baselines to block high-risk scopes for non-admin users.

Based on reporting by GBHackers.