Entra ID Actor Token User Impersonation Abuse

Last updated 19 days ago on 2025-09-18

Created 19 days ago on 2025-09-18

About

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.

Tags

Domain: CloudDomain: IdentityData Source: AzureData Source: Entra IDData Source: Entra Audit LogsUse Case: Identity and Access AuditUse Case: Threat DetectionTactic: Initial AccessTactic: Privilege EscalationLanguage: esql

Severity

medium

Risk Score

MITRE ATT&CK™

Initial Access (TA0001)(opens in a new tab or window)

↳ Valid Accounts (T1078)(opens in a new tab or window)

Privilege Escalation (TA0004)(opens in a new tab or window)

↳ Abuse Elevation Control Mechanism (T1548)(opens in a new tab or window)

False Positive Examples

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.

License

Elastic License v2(opens in a new tab or window)

Definition

Integration Pack: Prebuilt Security Detection Rules
Related Integrations: azure(opens in a new tab or window)
Query

from logs-azure.auditlogs-* metadata _id, _version, _index
| where azure.auditlogs.properties.initiated_by.user.displayName in (
    "Office 365 Exchange Online",
    "Skype for Business Online",
    "Dataverse",
    "Office 365 SharePoint Online",
    "Microsoft Dynamics ERP"
  ) and
  not azure.auditlogs.operation_name like "*group*" and
  azure.auditlogs.operation_name != "Set directory feature on tenant"
  and azure.auditlogs.properties.initiated_by.user.userPrincipalName rlike ".+@[A-Za-z0-9.]+\\.[A-Za-z]{2,}"
| keep
    _id,
    @timestamp,
    azure.*,
    client.*,
    event.*,
    source.*

Install detection rules in Elastic Security

Detect Entra ID Actor Token User Impersonation Abuse in the Elastic Security detection engine by installing this rule into your Elastic Stack.

To setup this rule, check out the installation guide for Prebuilt Security Detection Rules(opens in a new tab or window).