What is the CVSS score of EUVD-2026-31519?

EUVD-2026-31519 has a CVSS 3.1 base score of 9.1 (Critical). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N. EPSS exploitation probability: 0.1%.

Which versions of Microsoft Entra are affected by EUVD-2026-31519?

Microsoft Azure Active Directory B2C, a core identity service for enterprise customer and employee access, contains an unauthenticated authentication bypass allowing remote privilege escalation…. A patch is available.

How to fix or mitigate EUVD-2026-31519?

24 hours: Identify all Azure AD B2C / Microsoft Entra tenants in production and assess systems dependent on this service for authentication and access control. 7 days: Apply Microsoft's released patch to all affected Azure AD B2C instances, prioritizing tenants handling sensitive or regulated customer data. 30 days: Perform forensic review of authentication logs for unauthorized access patterns since vulnerability disclosure; validate patch effectiveness and document remediation.

Microsoft Entra EUVD-2026-31519

| CVE-2026-33843 CRITICAL

Authentication Bypass Using an Alternate Path or Channel (CWE-288)

2026-05-22 microsoft

GHSA-5gj2-5693-p684

Microsoft Authentication Bypass

9.1

CVSS 3.1 · NVD

Severity by source

NVD PRIMARY

9.1 CRITICAL

AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

None

Lifecycle Timeline

Analysis Generated

May 22, 2026 - 22:45 vuln.today

DescriptionCVE.org

Authentication bypass using an alternate path or channel in Microsoft Azure Active Directory B2C allows an unauthorized attacker to elevate privileges over a network.

AnalysisAI

Authentication bypass in Microsoft Azure Active Directory B2C (now part of Microsoft Entra) allows remote unauthenticated attackers to elevate privileges by reaching protected functionality through an alternate code path. The CVSS 9.1 vector (AV:N/AC:L/PR:N/UI:N) reflects network-reachable exploitation with no privileges and no user interaction, yielding high confidentiality and integrity impact against tenants relying on Azure AD B2C for identity. No public exploit identified at time of analysis and the issue is not listed in CISA KEV, but the unauthenticated-network profile and Microsoft self-reporting make this a high-priority advisory for any tenant using B2C.

Technical ContextAI

Azure AD B2C is Microsoft's customer-facing identity-as-a-service offering within the Microsoft Entra family, used to handle sign-up, sign-in, and federated identity for consumer applications via OAuth/OIDC and SAML flows. CWE-288 (Authentication Bypass Using an Alternate Path or Channel) describes a class where authentication is enforced on the primary path but a parallel endpoint, protocol handler, or flow variant skips or weakens that enforcement - for example, an unauthenticated administrative or token-issuance endpoint, an unintended SAML/OIDC flow, or a misrouted internal API. The affected CPE 'cpe:2.3:a:microsoft:microsoft_entra' confirms the service-side identity platform is the locus of the flaw rather than any on-premises component, meaning the fix is delivered server-side by Microsoft rather than via customer-installed updates.

RemediationAI

Patch available per vendor advisory: Microsoft has released a fix for Azure AD B2C / Microsoft Entra documented at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-33843, and because this is a cloud service the remediation is applied by Microsoft to the platform rather than requiring a customer-installed patch - administrators should consult MSRC to confirm their tenant region and ring is on the fixed service version. Defenders should additionally review B2C sign-in logs and audit logs for anomalous token issuance, unfamiliar application consent grants, and privilege changes since the disclosure window, and rotate any credentials or signing keys that may have been exposed through unauthorized flows. As compensating controls until tenant remediation is confirmed, restrict sensitive B2C-protected applications behind Conditional Access policies that require additional factors or trusted networks (trade-off: may break legitimate customer logins on unmanaged devices), tighten allowed redirect URIs and token lifetimes on B2C applications to shrink the abuse window, and disable any unused B2C user flows or custom policies that expand the attack surface.