OAuth consent attacks in Microsoft Entra ID are giving threat actors a stealthy path to cloud email, and even trusted apps like ChatGPT can become a vehicle if permissions are abused.
In this hypothetical case, a user in an Entra ID tenant adds the legitimate ChatGPT service principal and grants it Microsoft Graph OAuth permissions, including Mail.Read, offline_access, profile, and openid.
The key risk is not that ChatGPT is malicious, but that a phishing page or social engineering prompt can trick the user into approving a consent screen that silently grants persistent API access to their mailbox.
The Entra AuditLogs show two critical events tied together by a shared CorrelationId: Add service principal and Consent to application.
As Red Canary continues to observe OAuth application attacks in the wild, our Threat Research team is pivoting off real-world tradecraft to anticipate new innovations in attack techniques.
These logs reveal that a new third‑party app (ChatGPT, identified by its AppId and distinct AppOwnerOrganizationId) was successfully added to the tenant and then granted Mail.Read for the specific user principal.
Consent was non‑admin, this pattern aligns with common OAuth phishing tradecraft, where regular users are targeted to bypass stricter admin controls.
Once mail access is granted, attackers can abuse the app’s token to read inbound and outbound messages, harvest sensitive data, monitor password‑reset flows, and pivot into conversation‑hijacking or business email compromise (BEC) scenarios.
OAuth token abuse often bypasses MFA and traditional sign‑in detection because the app uses legitimate Graph APIs with valid tokens rather than suspicious logins.
OAuth Vulnerabilities in Entra ID
Effective detection starts with the “who, what, when, where, whence, how” questions driven by content Audit Logs.
Corresponds to the time in which the action occurred.
“At 2025-12-02T20:22:16″
| Operation | Field | Value | Description |
Consent to application | ActivityDateTime | 2025-12-02T20:22:16.2365366Z | The date and time that this event occurred. |
Investigators should confirm whether the consent came from the legitimate user, whether the application is sanctioned, and whether its requested scopes match organizational policy.
A high‑value analytic is to alert on non‑admin consent for a new third‑party application that requests one or more risky scopes such as Mail.Read, Files.Read all, or Chat.Read.
This requires correlating Consent to application and Add service principal events by CorrelationId, verifying that AppOwnerOrganizationId does not match the tenant or known Microsoft first‑party IDs, and checking ConsentContext.IsAdminConsent is False.
Enrichment with publisher reputation and app prevalence helps distinguish benign high‑use SaaS from rare, potentially adversary‑controlled registrations.
Because the oAuth2PermissionGrant structure is opaque, defenders should still parse ConsentAction.Permissions strings to extract the grant Id, ClientId, PrincipalId, ResourceId, and Scope for triage and targeted response.
Scopes that include Mail.Read or offline_access, especially on previously unseen apps, warrant priority review.
Mitigations
If an OAuth grant is deemed malicious or unsanctioned, responders should immediately revoke the specific oAuth2PermissionGrant and then remove the associated service principal from the tenant.
This cuts off the attacker’s token‑based access without changing the user’s password or credentials.From where did the action originate?
“This action was performed from the following IP address: 3.89.177.26.”
| Operation | Field | Value | Description |
Consent to application | InitiatedBy.user.ipAddress | 3.89.177.26 | The IP address from which the actor performed the action. |
Longer‑term, organizations should tighten Entra user consent settings to reduce the attack surface.
Coupled with continuous monitoring for risky OAuth apps in Defender for Cloud Apps and targeted hunting for suspicious consent patterns, these controls help ensure that even powerful tools like ChatGPT cannot be quietly turned into an attacker’s inbox backdoor.
Microsoft allows admins to disable user consent entirely, restrict consent to apps from verified publishers with low‑impact permissions, or adopt Microsoft‑managed consent baselines that block known high‑risk scopes for non‑admins.
Follow us on Google News, LinkedIn, and X to Get Instant Updates and Set GBH as a Preferred Source in Google.
