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CVE-2026-40379 Microsoft Enterprise Security Token Service (ESTS) Spoofing Vulnerability

CVE-2026-40379 is a critical (CVSS 9.3) spoofing vulnerability in Microsoft's Azure Entra ID Enterprise Security Token Service (ESTS) where exposure of sensitive information allows an unauthorized attacker to perform spoofing over a network. Microsoft has already fully mitigated this vulnerability on their service side, requiring no customer action. The CVE was published for transparency as no patch or workaround is required for users of the affected cloud service.
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