CVE-2026-40379 Microsoft CVE debrief

Who should care

Microsoft Entra ID administrators, identity and access management teams, security operations, and any organization that depends on Entra ID for authentication, federation, or tenant identity controls should review this issue promptly.

Technical summary

The official record maps CVE-2026-40379 to Microsoft Entra ID and a CWE-200 category (Exposure of Sensitive Information to an Unauthorized Actor). The CVSS vector supplied by NVD shows network attack surface, low complexity, no privileges required, and user interaction required, with changed scope and high confidentiality/integrity impact. The vendor-facing description indicates that the information exposure can be leveraged for spoofing over the network, so identity validation and trust assumptions are the central concern.

Defensive priority

Critical. Treat as a high-priority identity security issue and follow Microsoft’s advisory guidance as soon as possible, especially in environments where Entra ID trust decisions or authentication flows are business-critical.

Recommended defensive actions

• Review the Microsoft Security Response Center advisory for CVE-2026-40379 and follow the vendor’s remediation guidance.
• Assess where Microsoft Entra ID is used for authentication, federation, or identity trust decisions, and prioritize those tenants and applications.
• Monitor for anomalous sign-in activity, spoofing indicators, or unexpected identity-related behavior while remediation is underway.
• Validate that identity and access management controls, conditional access policies, and alerting are functioning as expected.
• Document internal exposure and response status for all tenants and business units that rely on Entra ID.

Evidence notes

This debrief is based only on the supplied official vulnerability records. The NVD feed lists Microsoft as the affected vendor/product (Entra ID), a CVSS 3.1 vector of AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N, and CWE-200. The only reference supplied in the NVD record is the Microsoft Security Response Center advisory URL. No exploit details, weaponized reproduction steps, or additional affected-version data were provided.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.