Critical Microsoft Entra ID Vulnerability Allows Attackers to Gain Complete Administrative Control CyberDudeBivash Authority Report

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Executive Summary

  • A recently disclosed critical vulnerability in Microsoft Entra ID (formerly Azure Active Directory) could have allowed attackers to impersonate any user, including Global Administrators, across any tenant, due to mis-validated tokens and legacy API issues. WIRED+2dirkjanm.io+2

  • Discovered by researcher Dirk-jan Mollema (Outsider Security), these flaws involved Actor Tokens issued via legacy Access Control Service plus a flaw in the outdated Azure AD Graph API, allowing these tokens to be used across tenants. dirkjanm.io+1

  • Microsoft was notified 14 July 2025; fix rolled out rapidly. WIRED+1

  • Impact: tenant takeover, creation of admin accounts, modification of configuration, complete compromise of Entra ID resources.

Background & Vulnerability Details

What are Actor Tokens & Azure AD Graph API

  • Actor Tokens are internal service-to-service impersonation tokens used historically by Microsoft’s backend services. They were not intended to be exposed or usable in cross-tenant scenarios. dirkjanm.io+1

  • Azure AD Graph API is Microsoft’s older API for managing Azure AD (predecessor to Microsoft Graph). It has been in the process of deprecation, but in many environments it remained active. The flaw: Graph failed to properly validate the origin tenant for certain Actor Token usage. dirkjanm.io+1

The Exploit Chain

  1. Attacker obtains Actor Token in their own lab or test tenant.

  2. Calls to Azure AD Graph API using that Actor Token are accepted even when made across tenants (since tenant validation was broken).

  3. Impersonates users including Global Admins in other tenants.

  4. With admin privileges, attacker can manipulate user accounts, alter configurations, grant themselves elevated roles, exfiltrate data across tenant, etc. dirkjanm.io+2iTnews+2

Affected Systems & Exploitability

  • Any organization using Entra ID/Azure AD where the legacy Graph API was enabled or not sufficiently locked down. WIRED+1

  • Tenants which still relied on legacy actor token mechanisms from Access Control Service.

  • Tenants with weak policies around application registrations, service principals, or tenant settings that allow cross-tenant actor scenarios.

Detection & Indicators (IoCs)

Here are what to watch for in your environments:

  • Unusual Actor Token issuance / use logs.

  • Calls to Azure AD Graph API from unexpected tenants.

  • Creation of administrative accounts from non-trusted or new identities.

  • Cross-tenant impersonation / unexpected global admin activity.

  • Configuration changes in user roles / permissions unexpectedly.

  • Unexpected service principal credentials / application registrations mapping to actor-token flows.

Threat Hunting Playbook

Sample SIEM / Log Queries

A. Detect Graph API requests using Actor Tokens

index=azure_ad_logs
| where Resource == "Graph API"
| where TokenType == "ActorToken"
| where TenantId != SourceTenantId
| stats count by AppId, Caller, Time
| where count > threshold

B. Detect new Global Admins via non-trusted accounts

index=azure_audit
| where OperationName == "AddMemberToRole" and RoleName == "Global Administrator"
| where InitiatedBy NOT IN (trustedAdminList)
| table Time, Initiator, TargetUser

C. Monitor application registration changes

index=azure_ad_logs
| where OperationName in ("AddServicePrincipalCredential", "UpdateApplication")
| where ApplicationId NOT IN trustedAppList
| alert if seen

Immediate Mitigation Steps

  1. Disable usage of Actor Tokens / retire the legacy Access Control Service where possible.

  2. Confirm Azure AD Graph API is deprecated / disable or restrict access.

  3. Rotate credentials and audit all Global Administrators.

  4. Enforce Conditional Access & require MFA + phishing-resistant auth for privileged roles.

  5. Restrict application registrations and service principals: only a small, audited set.

Long-Term Measures

  • Enforce least privilege on all roles (Global Admin, Application Admin, etc.).

  • Use Privileged Identity Management (PIM) to require approval flows for elevation to high privileges.

  • Regularly review & audit cross-tenant trusts, app registrations, service principals.

  • Monitor for deprecated APIs and legacy token flows in your environment.

  • Implement continuous monitoring & token validation logic in logs.

Business, Compliance & Risk Impact

  • Data exfiltration risk across tenants (if multi-tenant setup).

  • Regulatory exposure: violation of data protection laws if cross-tenant data is inappropriately accessed.

  • Trust & reputational damage.

  • Insurance implications: insurers expect strong IAM and deprecation of legacy identity systems.

Recommendations & Roadmap

  • Immediately inventory all tenants for Actor Token usage & Graph API calls.

  • Apply Microsoft’s patches and confirm remedial updates have been deployed in your tenant.

  • Enforce Zero Trust for identity: MFA, device compliance, conditional access.

  • Retire deprecated APIs / migrate to Microsoft Graph exclusively.

  • Conduct tabletop exercises simulating this vulnerability exploit path.

Summary

This vulnerability is near the top of what you fear in identity compromise: almost full takeover of Entra ID tenants across Microsoft’s cloud. Microsoft did patch rapidly — but the fact the vulnerability existed shows how deeply dangerous legacy token mechanisms and old APIs can be. CyberDudeBivash stance: audit, patch, enforce, and never trust legacy identity artifacts.


#CyberDudeBivash #EntraID #AzureAD #SecurityVulnerability #ActorTokens #GlobalAdmin #CloudIdentity #ThreatIntel #ZeroTrust #IdentitySecurity

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