Note: This analysis is based on publicly available information from source article. Facts are clearly separated from technical analysis.
Executive Summary
Incident Overview
On September 22, 2026, a high-severity security incident, dubbed "Rogue External MFA Provider Credential Theft," was discovered. This incident involves a sophisticated attack, known as TrustSink, which allows hackers with privileged access to register a rogue external MFA provider that steals users' passwords during legitimate login attempts. The attack affects organizations that use Microsoft Entra, which supports external MFA providers.
Impact
At least one company, Microsoft, has been affected by this incident. The exact number of devices and duration of the attack are unknown. This incident highlights the importance of robust security measures, particularly in the context of multifactor authentication.
Why it Matters
This incident demonstrates the potential for attackers to exploit vulnerabilities in external MFA providers, compromising user credentials and potentially leading to further attacks. It emphasizes the need for organizations to implement and maintain robust security controls, including regular security audits and employee education.
What Happened: Timeline
✅ Verified Facts
| Time | Event |
|---|---|
| 2025 | Dirk-Jan Mollema presented a talk titled 'Bringing Your Own Identity in Entra ID' at x33fcon. |
| 2026-09-22 | Security researchers developed an attack that lets hackers with privileged access register a rogue external MFA provider that steals users' passwords during legitimate login attempts. |
Technical Deep Dive
Understanding External MFA Providers
What is it? External MFA providers are third-party authentication services that organizations can use to satisfy multifactor authentication requests. Microsoft Entra supports external MFA providers, allowing organizations to integrate these services into their authentication workflows.
How does it work? When a user attempts to log in, the external MFA provider is contacted to verify the user's identity. The provider returns a signed token to Entra, which then authenticates the user. In the case of the TrustSink attack, the attacker registers a rogue external MFA provider, which captures the user's password in plaintext before returning a valid signed token to Entra.
Security considerations The TrustSink attack highlights the potential for attackers to exploit vulnerabilities in external MFA providers. This emphasizes the need for organizations to carefully evaluate and monitor their external MFA providers to prevent such attacks.
Related Technology: Authentication Methods Policy
The Authentication Methods Policy is a critical component of Microsoft Entra's external MFA provider integration. It allows organizations to configure and manage the external MFA providers that are allowed to authenticate users. In the context of the TrustSink attack, the attacker must modify the Authentication Methods Policy to register the rogue external MFA provider.
Related Technology: Consent Grants
Consent grants are used to authorize external MFA providers to access user credentials. In the case of the TrustSink attack, the attacker must create a consent grant to allow the rogue external MFA provider to access user credentials.
Analysis: What Went Wrong
Technical Root Cause
The technical root cause of the TrustSink attack is the vulnerability in Microsoft Entra's external MFA provider integration. The attacker is able to register a rogue external MFA provider, which captures user credentials in plaintext.
Contributing Factors
The contributing factors to the TrustSink attack include the attacker's privileged access to the Entra account and the lack of robust security controls in place to detect and prevent such attacks.
Lessons for Security Professionals
Key Takeaways
- Implement robust security controls: Organizations must implement and maintain robust security controls, including regular security audits and employee education, to prevent such attacks.
- Monitor external MFA providers: Organizations must carefully evaluate and monitor their external MFA providers to prevent vulnerabilities like the one exploited in the TrustSink attack.
- Limit privileged access: Organizations must limit privileged access to sensitive systems and data to prevent attackers from exploiting vulnerabilities like the one in the TrustSink attack.
Prevention & Detection
How to Prevent
- Implement robust security controls: Regular security audits and employee education can help prevent such attacks.
- Monitor external MFA providers: Carefully evaluate and monitor external MFA providers to prevent vulnerabilities like the one exploited in the TrustSink attack.
- Limit privileged access: Limit privileged access to sensitive systems and data to prevent attackers from exploiting vulnerabilities like the one in the TrustSink attack.
How to Detect
- Monitor authentication logs: Monitor authentication logs to detect suspicious activity, such as multiple failed login attempts.
- Implement anomaly detection: Implement anomaly detection systems to detect unusual patterns of behavior that may indicate a security incident.
Related Certification Topics
View related certification topics
Security+ (CompTIA)
- Domain 1.0: Network Security: Understanding network security concepts, including authentication and authorization.
- Domain 2.0: Compliance and Operational Security: Understanding compliance and operational security concepts, including security policies and procedures.
CC (CompTIA)
- Domain 1.0: Network Security: Understanding network security concepts, including authentication and authorization.
- Domain 2.0: Compliance and Operational Security: Understanding compliance and operational security concepts, including security policies and procedures.
CySA+ (CompTIA)
- Domain 1.0: Security and Risk Management: Understanding security and risk management concepts, including threat analysis and mitigation.
- Domain 2.0: Vulnerability Management: Understanding vulnerability management concepts, including vulnerability assessment and remediation.
CISSP (ISC2)
- Domain 1: Security and Risk Management: Understanding security and risk management concepts, including threat analysis and mitigation.
- Domain 2: Asset Security: Understanding asset security concepts, including data classification and access control.
OSCP (Offensive Security)
- Domain 1: Network Security: Understanding network security concepts, including authentication and authorization.
- Domain 2: Vulnerability Analysis: Understanding vulnerability analysis concepts, including vulnerability assessment and exploitation.
CISM (ISACA)
- Domain 1: Information Security Governance: Understanding information security governance concepts, including risk management and compliance.
- Domain 2: Information Risk Management: Understanding information risk management concepts, including threat analysis and mitigation.
CISM (ISACA)
- Domain 3: Information Security Program Development and Management: Understanding information security program development and management concepts, including security policies and procedures.
CISM (ISACA)
- Domain 4: Information Security Incident Management: Understanding information security incident management concepts, including incident response and recovery.
CISM (ISACA)
- Domain 5: Information Security Technology and Information Systems: Understanding information security technology and information systems concepts, including security controls and countermeasures.
Source
This analysis is based on: https://www.bleepingcomputer.com/news/security/rogue-external-mfa-providers-can-steal-passwords-during-logins/
This incident analysis is provided for educational purposes. Facts are cited from the source article, while technical analysis represents professional interpretation.