CVE-2026-83711 in Entra
Summary
by MITRE • 09/04/2026
Authorization bypass through user-controlled key in Microsoft Azure Active Directory B2C allows an unauthorized attacker to elevate privileges over a network.
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Analysis
by VulDB Data Team • 09/04/2026
The vulnerability described represents a critical authorization bypass within the Microsoft Azure Active Directory B2C service, specifically stemming from improper validation of user-supplied input used as keys for access control decisions. In secure software architecture, authorization mechanisms must rely on server-side state or cryptographically signed tokens that cannot be trivially manipulated by an end-user. However, in this instance, the system accepts a key provided directly through user-controlled parameters and uses it to determine privilege levels without sufficient verification against authoritative identity sources. This flaw allows an attacker who possesses valid credentials for one account to manipulate request payloads, effectively substituting their own session identifiers or permission keys with those belonging to accounts possessing higher privileges. By doing so, the attacker circumvents standard access control checks, achieving unauthorized elevation of privileges within the application environment.
From a technical perspective, this issue aligns closely with CWE-284 Improper Access Control and CWE-613 Insufficient Session Expiration. The core deficiency lies in the failure to bind session state or permission grants securely to the authenticated user identity on the server side. Instead of validating that the requested action is permitted for the specific principal making the request, the system trusts a key value transmitted by the client. This design pattern violates fundamental security principles such as least privilege and defense in depth. When an attacker intercepts network traffic or crafts malicious API requests, they can inject arbitrary keys that map to administrative roles or sensitive data scopes assigned to other users. The server processes these requests based on the injected key rather than verifying the actual identity of the requester against its internal authorization database, leading to a complete breakdown in access enforcement.
The operational impact of this vulnerability is severe, as it enables remote attackers to perform actions reserved for administrators or privileged service accounts without prior authentication or with minimal credentials. This can lead to unauthorized modification of user profiles, extraction of sensitive personal data protected under regulations such as GDPR or CCPA, and potential compromise of downstream systems that trust the Azure AD B2C identity assertions. Attackers could also use this elevated access to disable security logging, alter multi-factor authentication settings for other users, or exfiltrate proprietary business logic embedded in custom policies. The ability to elevate privileges over a network means that exploitation does not require physical proximity or local system access, making it highly scalable and dangerous in cloud-native environments where identity is the primary perimeter.
This vulnerability maps directly to several techniques within the MITRE ATT&CK framework for both on-premises and cloud-based threats. It corresponds primarily to T1078 Valid Accounts, as attackers leverage legitimate credentials combined with manipulated parameters to gain access they are not entitled to. Furthermore, it relates to T1528 Steal Application Access Token if the keys involve token manipulation, or more broadly to privilege escalation techniques that exploit misconfigured identity providers. The attack vector typically involves HTTP parameter pollution or direct injection of session identifiers in API calls targeting Azure AD B2C endpoints such as sign-in policies or custom user flows where permission scopes are defined dynamically based on input parameters.
Mitigation strategies must focus on enforcing strict server-side validation and eliminating reliance on client-supplied values for security-critical decisions. Developers should ensure that all authorization checks are performed against immutable, server-generated session tokens rather than mutable keys passed in request bodies or headers. Implementing robust input validation to reject unexpected parameter formats can reduce the attack surface, but the primary fix requires architectural changes to decouple identity verification from user-controlled inputs. Microsoft has likely released security updates addressing this specific flaw by hardening the token generation and validation logic within Azure AD B2C services. Organizations relying on these features should immediately apply all available platform patches and review custom policy configurations for any reliance on dynamic key injection patterns. Additionally, enabling comprehensive audit logging allows administrators to detect anomalous privilege escalation attempts in real time, providing a critical layer of defense-in-depth while technical remediation is deployed across the infrastructure.