Threat actors are constantly adapting, and one increasingly abused technique inside Microsoft Entra ID is OAuth consent abuse.
A newly documented attack scenario demonstrates how a malicious—or overly permissive—third-party application that resembles a trusted service like ChatGPT can gain access to a corporate user’s inbox without ever stealing a password.
The risk isn’t about exploiting vulnerabilities. It’s about exploiting trust and user consent.
How OAuth Consent Abuse Works
OAuth (Open Authorization) allows users to grant applications limited access to their data without sharing credentials.
Inside Entra ID, when a user connects a third-party app to their Microsoft account, they’re shown a consent prompt listing requested permissions.
Attackers abuse this workflow by:
- Creating or disguising an application as a trusted tool
- Requesting high-impact permissions such as Mail.Read
- Tricking the user into approving the consent request
Once accepted, the app can access mailbox data directly through Microsoft Graph APIs — silently and persistently.
No password theft.
No MFA bypass.
Just legitimate API access granted by the victim.
Real-World Case Study: A Familiar Pattern
Security researchers at Red Canary analyzed a scenario in which a corporate user added ChatGPT as a third-party service principal within an Entra ID tenant.
The non-admin user consented to the following OAuth scopes:
- Mail.Read
- offline_access
- profile
- openid
The activity occurred on December 2, 2025, at 20:22:16 UTC and was traced to IP address 3.89.177.26.
In this particular case, the application was verified to be the legitimate OpenAI-owned ChatGPT service. However, the investigative workflow mirrored a real-world malicious incident Red Canary had previously observed.
The takeaway:
The platform isn’t the problem. The consent pattern is.
Any third-party app granted Mail.Read can silently read every email in a user’s inbox.
Why This Attack Is So Dangerous
By default, Entra ID allows non-admin users to consent to many third-party applications.
This means:
- A standard employee
- With no elevated privileges
- Can authorize an external app
- That gains direct API access to sensitive corporate email
In a real attack scenario, threat actors could:
- Create a convincingly named app
- Deliver a phishing link
- Prompt the victim to “Connect”
- Harvest internal communications, attachments, credentials, and business-sensitive data
All without triggering traditional credential compromise alerts.
What Happens in the Logs?
When a user consents to an application, two key audit events are generated inside Entra ID:
- Add service principal
- Consent to application
Both share the same CorrelationId, allowing security teams to reconstruct the full consent chain.
Detection teams should closely monitor:
- Non-admin consent grants
- Newly introduced third-party applications
- High-risk OAuth scopes
One particularly important audit field is:
AppOwnerOrganizationId
If this value does not match:
- Your tenant ID
- Or known Microsoft first-party identifiers
The application is third-party and should be treated with caution.
Commonly Abused OAuth Scopes
The most frequently abused permissions in consent-based attacks include:
- Mail.Read
- Files.Read.All
- Chat.Read
- Sites.Read.All
Each grants direct access to sensitive collaboration or communication data.
Immediate Remediation Steps
If a malicious or unauthorized consent grant is identified:
- Revoke the OAuth permission grant using the grant ID from the audit logs
- Remove the service principal from the tenant using its object ID
Both steps can be executed via Microsoft Graph PowerShell.
Speed matters. The longer the consent remains active, the longer attackers retain inbox access.
Strengthening Prevention Controls
Microsoft provides configurable consent policies to reduce exposure.
Organizations can choose from:
1️⃣ Admin Approval for All Apps (Most Secure)
- Requires administrator approval for every application
- Eliminates non-admin consent risk
2️⃣ Verified Publishers + Low-Risk Permissions
- Allows limited user consent
- Restricts high-impact permissions
3️⃣ Microsoft Recommended Settings
- Applies Microsoft’s current user consent guidelines
- Balances operational flexibility with security
For high-risk environments, restricting non-admin consent significantly reduces the attack surface.
The Bigger Lesson
OAuth consent abuse is not a vulnerability in ChatGPT or Entra ID. It is a trust exploitation technique.
Attackers no longer need passwords if users willingly grant API access.
As organizations increasingly rely on SaaS integrations, identity security must evolve from credential monitoring to consent monitoring.
Because sometimes the compromise doesn’t start with stolen credentials.
It starts with a single click on “Accept.”
