Detecting Suspicious OAUTH Application Consent

Detecting Suspicious OAuth Application Consent

Overview

Illicit consent grant attacks trick users into granting excessive permissions to malicious OAuth applications in Azure AD / Microsoft Entra ID. This skill uses the Microsoft Graph API to enumerate OAuth2 permission grants, analyze application permissions for overly broad scopes, review directory audit logs for consent events, and flag high-risk applications based on publisher verification status and permission scope.

When to Use

• When investigating security incidents that require detecting suspicious oauth application consent
• When building detection rules or threat hunting queries for this domain
• When SOC analysts need structured procedures for this analysis type
• When validating security monitoring coverage for related attack techniques

Detection Gaps & Validation

The most dangerous grants this Graph workflow can miss:

• /oauth2PermissionGrants returns only DELEGATED consent. Application permissions (app roles) live under servicePrincipals/{id}/appRoleAssignments — querying only oauth2PermissionGrants misses app-only Mail.Read/Files.ReadWrite.All/Directory.ReadWrite.All, which run with no signed-in user and are the worst case.
• ConsentType == "AllPrincipals" (tenant-wide admin consent) is far higher risk than "Principal" (single user) — flag AllPrincipals explicitly rather than treating all grants equally.
• Programmatic grants show as Add app role assignment to service principal / Add delegated permission grant in directoryAudits, not just Consent to application — watching only the latter misses them.
• offline_access scope = refresh-token persistence — treat as high-signal even when other scopes look benign.
• Null verifiedPublisher isn't malicious by itself (many legit internal apps) — combine with risky scope + recent creation to cut FP.

Validate: confirm the app token actually carries Application.Read.All (with only Directory.Read.All the enumeration returns partial data and looks clean); cross-check a flagged app against the directoryAudits consent event to recover the granting user and IP; maintain an allowlist of approved appIds to suppress known-good apps.

Prerequisites

• Azure AD / Entra ID tenant with Global Reader or Security Reader role
• Microsoft Graph API access with Application.Read.All, AuditLog.Read.All, Directory.Read.All
• Python 3.9+ with msal, requests
• App registration with client secret or certificate for authentication

Steps

1. Authenticate to Microsoft Graph using MSAL client credentials flow
2. Enumerate all OAuth2 permission grants via /oauth2PermissionGrants
3. List service principals and their assigned application permissions
4. Query directory audit logs for Consent to application events
5. Flag applications with high-risk scopes (Mail.Read, Files.ReadWrite.All, etc.)
6. Check publisher verification status for each application
7. Generate risk report with remediation recommendations

Expected Output

• JSON report listing all OAuth apps with granted permissions, risk scores, unverified publishers, and suspicious consent patterns
• Audit trail of consent grant events with user and IP details