The Looming Shadow of “Actor Tokens”: How Legacy Code Could Reshape the Future of Entra ID Security
Imagine a scenario where a single, overlooked piece of code from the past could unlock the keys to every company’s cloud identity system. That’s the chilling reality exposed by security researcher Dirk-jan Mollema’s recent discovery regarding Microsoft Entra ID (formerly Azure AD). The vulnerability, stemming from undocumented “actor tokens” and a flaw in the Azure AD Graph API, highlights a critical truth: even the most robust security architectures are only as strong as their weakest, and often oldest, components.
The Anatomy of a Silent Breach
At the heart of this issue lies the “actor token,” a legacy authentication mechanism initially designed for communication between SharePoint applications and Microsoft’s internal services. These tokens, crucially, are unsigned. This means they can be forged to impersonate any user within an Entra ID tenant, granting attackers potentially limitless access. What’s more alarming is that these tokens operate outside the purview of standard security controls like Multi-Factor Authentication (MFA) and Conditional Access policies.
Mollema’s research revealed that by manipulating the tenant ID and user netID within an actor token, he could access data in entirely different Entra ID environments via the deprecated Azure AD Graph API. This wasn’t a theoretical risk; he successfully demonstrated the ability to escalate privileges to Global Administrator level – the highest level of access – without triggering any logging within the targeted tenant. The lack of logging is perhaps the most insidious aspect of this vulnerability, creating a “ghost in the machine” scenario where attackers can operate undetected.
“This whole Actor token design is something that never should have existed,” says Mollema. “They lack the proper required security controls, and their existence represents a fundamental flaw in how Microsoft has historically approached service-to-service authentication.”
Beyond the Patch: The Future of Identity Security
Microsoft has since patched the vulnerability (CVE-2025-55241) and announced plans to remove actor tokens altogether. However, the incident serves as a stark warning about the challenges of managing complex, evolving identity and access management (IAM) systems. The reliance on legacy components, even for internal processes, introduces significant risk. The future of Entra ID security – and IAM in general – will likely be shaped by several key trends:
1. The Rise of Zero Trust Architectures
The actor token vulnerability underscores the limitations of traditional perimeter-based security. Zero Trust, a security framework based on the principle of “never trust, always verify,” is gaining momentum. This means verifying every user and device, regardless of location, before granting access to resources. Implementing robust Zero Trust principles, including micro-segmentation and continuous authentication, can significantly mitigate the impact of compromised credentials or rogue tokens.
2. Enhanced Token Security and Validation
The lack of signing on actor tokens was a critical flaw. Expect to see a shift towards more secure token formats, such as JSON Web Tokens (JWTs) with robust digital signatures. Furthermore, stricter token validation processes, including regular revocation checks and tighter integration with IAM systems, will be essential. The industry is moving towards passwordless authentication methods, which can further reduce the attack surface.
3. The Importance of Comprehensive Logging and Monitoring
The absence of logging surrounding actor token usage was a major obstacle to detection. Organizations need to invest in comprehensive logging and monitoring solutions that capture all authentication events, including those related to service-to-service communication. Security Information and Event Management (SIEM) systems, coupled with advanced threat detection capabilities, are crucial for identifying and responding to anomalous activity.
Entra ID, like all cloud services, is a constantly evolving target. Proactive security measures are no longer optional.
Regularly review and audit your Entra ID configuration, paying close attention to legacy integrations and service accounts. Ensure that all applications and services are using the latest authentication protocols and security best practices.
4. The Shift to Graph-Based Security
While the Azure AD Graph API was the vector for exploitation in this case, the underlying concept of using graph databases to represent relationships between users, devices, and resources is becoming increasingly important. Graph-based security analytics can help identify patterns of malicious activity that might otherwise go unnoticed. Microsoft’s move to Microsoft Graph is a step in this direction, offering a more unified and secure approach to data access.
The Ripple Effect: Third-Party Applications and Supply Chain Risk
The impact of vulnerabilities like this extends beyond direct Entra ID users. Many third-party applications rely on Entra ID for authentication. A compromise of Entra ID could have cascading effects, potentially impacting thousands of organizations. This highlights the growing importance of supply chain security and the need for organizations to carefully vet the security practices of their vendors.
Did you know that 46% of environments had passwords cracked last year, nearly doubling from 25% the previous year? This statistic, from the Picus Blue Report 2025, underscores the ongoing challenges of password security and the need for more robust authentication methods.
Frequently Asked Questions
What are “actor tokens”?
Actor tokens are undocumented authentication mechanisms used internally by Microsoft and for communication with some SharePoint applications. They are unsigned, allowing for impersonation of users without proper security controls.
How was this vulnerability exploited?
The vulnerability was exploited by manipulating the tenant ID and user netID within an actor token and sending it to the deprecated Azure AD Graph API. This allowed the attacker to access data in other Entra ID tenants and escalate privileges.
What steps can organizations take to protect themselves?
Organizations should implement Zero Trust principles, enhance token security, invest in comprehensive logging and monitoring, and regularly audit their Entra ID configuration. Staying up-to-date with Microsoft security advisories is also crucial.
Is Entra ID still secure after the patch?
While the immediate vulnerability has been patched, the incident highlights the importance of ongoing vigilance and proactive security measures. Organizations should continue to monitor their Entra ID environments for suspicious activity and implement best practices to mitigate future risks.
The actor token incident is a wake-up call. The future of Entra ID security – and the security of cloud identity systems in general – depends on a proactive, layered approach that addresses both current threats and the inherent risks of legacy code and complex integrations. What are your predictions for the evolution of cloud identity security in the coming years? Share your thoughts in the comments below!
Learn more about strengthening your authentication practices: see our guide on Multi-Factor Authentication best practices.
Dive deeper into the principles of Zero Trust: explore our coverage of Zero Trust security models.
Stay informed about the latest security advisories from Microsoft: Microsoft Security Response Center.
