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CVE-2026-77903 – Authentication Bypass Leading to Privilege Escalation – Microsoft Dataverse

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Summary

CVE-2026-77903 is a critical authentication bypass by spoofing vulnerability (CWE-290) affecting Microsoft Dataverse. The flaw allows an unauthorized, unauthenticated attacker to spoof authentication over the network and elevate privileges within the service. Microsoft rates the issue CRITICAL with a CVSS v3.1 base score of 9.0.

Technical details

  • Root cause: Improper authentication validation in Microsoft Dataverse allows an attacker to spoof the authentication process (CWE-290: Authentication Bypass by Spoofing).
  • Trigger conditions: No authentication or user interaction is required to exploit the vulnerability; the attack is executed remotely over the network, though Microsoft rates attack complexity as High.
  • Attack vector: Network (AV:N) — exploitation does not require local or physical access, adjacent network positioning, prior privileges (PR:N), or victim interaction (UI:N).
  • Impact: Successful exploitation results in a scope change (S:C) with high impact to confidentiality, integrity, and availability (C:H/I:H/A:H), meaning an attacker can elevate privileges and potentially affect resources beyond the initially vulnerable component within the Dataverse environment.

Affected software

  • Microsoft Dataverse — affects the service generally, with no distinct customer-managed version range published by Microsoft. Dataverse is delivered as a hosted/managed cloud service, and Microsoft has tagged this advisory as applying to an "exclusively hosted service."

Severity

  • CVSS v3.1 Base Score: 9.0 (Critical)
  • Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H/E:U/RL:O/RC:C

Mitigation and recommended actions

  • Immediate: Because Microsoft Dataverse is an exclusively hosted/managed cloud service, Microsoft is responsible for deploying the fix at the platform level; the CVE record indicates an official remediation level (RL:O) with a confirmed report (RC:C). Organizations should confirm with Microsoft/M365 admin communications that the patch has been applied to their tenant and monitor the MSRC advisory page for any tenant-side action items.
  • If no patch confirmation is available: Review Dataverse environment access logs and Entra ID (Azure AD) sign-in logs for anomalous or spoofed authentication attempts, enforce Conditional Access and MFA on all accounts with access to Dataverse environments, and restrict Dataverse API/connector access to trusted networks and applications until patch application is confirmed.
  • Continue to follow the principle of least privilege for Dataverse security roles and regularly audit privileged role assignments, since this vulnerability’s impact is privilege escalation.

References

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