CVE-2025-13909 in Identity Server
Summary
by MITRE • 08/06/2026
The system accepts authentication requests without sufficient validation to enforce tenant isolation when using Email OTP, SMS OTP, or Magic Link as first-factor authenticators. This failure to adequately separate user data between tenants can lead to the exposure of personally identifiable information.
Successful exploitation allows an attacker to disclose personally identifiable information of users in different tenants, resulting in privacy violations and potential regulatory non-compliance. This may include unauthorized access to user details such as mobile numbers.
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Analysis
by VulDB Data Team • 08/06/2026
This vulnerability represents a critical tenant isolation failure in multi-tenant authentication systems where email otp sms otp and magic link mechanisms do not properly validate tenant boundaries during the first factor authentication process. The flaw enables cross-tenant data leakage through insufficient validation controls that should prevent users from one tenant accessing authentication flows intended for another tenant. This type of vulnerability aligns with cwe 284 access control issues and specifically manifests as a lack of proper authorization checks within the authentication pipeline. The technical implementation appears to lack adequate tenant context verification before processing authentication requests, allowing malicious actors to exploit the system by manipulating authentication parameters or session states to gain unauthorized access to user data from different organizational tenants.
The operational impact of this vulnerability extends beyond simple data exposure to encompass serious privacy violations and regulatory compliance risks including potential violations of gdpr ccpa and other data protection frameworks. When attackers successfully exploit this weakness they can access personally identifiable information such as mobile phone numbers email addresses and potentially other user attributes that belong to accounts in different tenants. This creates a significant risk for organizations relying on multi-tenant architectures where customer isolation is paramount for maintaining service level agreements and protecting sensitive business data. The vulnerability essentially undermines the fundamental security principle of separation of duties by allowing unauthorized cross-tenant access to authentication mechanisms.
Security controls should be strengthened through mandatory tenant validation at authentication request processing stages with comprehensive session management that enforces proper tenant boundaries. Organizations must implement robust input validation and authorization checks that verify tenant context before proceeding with authentication flows. The implementation should include proper session isolation mechanisms that prevent session hijacking or manipulation attacks targeting different tenant contexts. Additionally organizations should consider implementing additional security controls such as tenant-specific authentication tokens and enhanced monitoring of authentication patterns that could indicate cross-tenant access attempts. From an att&ck perspective this vulnerability maps to privilege escalation techniques and credential access phases where attackers leverage insufficient validation to move laterally between tenant environments.
Mitigation strategies must include comprehensive code reviews to identify all authentication entry points and ensure tenant context validation is enforced at every stage of the authentication process. Organizations should implement proper logging and monitoring capabilities that can detect anomalous authentication patterns or unauthorized cross-tenant access attempts. Regular security testing including penetration testing of authentication flows should be conducted to validate tenant isolation controls. The solution architecture should incorporate tenant-aware authentication services where each tenant has properly isolated authentication contexts with no shared state between different tenant sessions. This vulnerability demonstrates the critical importance of maintaining proper separation boundaries in multi-tenant systems and the severe consequences when these boundaries are compromised through inadequate validation mechanisms that should be enforced at the core of all authentication processes.