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Entra ID Actor Token User Impersonation Abuse

Identifies potential abuse of actor tokens in Microsoft Entra ID audit logs. Actor tokens are undocumented backend mechanisms used by Microsoft for service-to-service (S2S) operations, allowing services to perform…

Description

Identifies potential abuse of actor tokens in Microsoft Entra ID audit logs. Actor tokens are undocumented backend mechanisms used by Microsoft for service-to-service (S2S) operations, allowing services to perform actions on behalf of users. These tokens appear in logs with the service's display name but the impersonated user's UPN. While some legitimate Microsoft operations use actor tokens, unexpected usage may indicate exploitation of CVE-2025-55241, which allowed unauthorized access to Azure AD Graph API across tenants before being patched by Microsoft.

Detection logic

Its licence does not clear it for publishing here

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Detection requirements

Platform
ContainersESXiIaaSIdentity ProviderLinuxmacOSNetwork DevicesOffice SuiteSaaSWindows

The rule states no platform. This is derived from the 3 ATT&CK techniques it maps to.

Known benign triggers

  • Creating specific groups via the Exchange Online PowerShell module will make Exchange use an Actor token on your behalf. The rule excludes group operations and directory feature operations to reduce false positives from these legitimate administrative activities.

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