CVE-2026-40379Network attack vector

Identity spoofing via undisclosed information exposure

Published May 12, 2026 · Updated May 12, 2026

Information exposure in Microsoft Entra allows remote attackers to spoof identities over a network after required user interaction. Microsoft has not published the information exposed, the request path involved, or the operation that mishandles untrusted input. Successful exploitation discloses sensitive information and corrupts identity trust decisions, with no reported ability to interrupt the service.

CVSS severity9.3
Critical
EPSS probability0.91%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Information exposure in Microsoft Entra allows remote attackers to spoof identities over a network after required user interaction. Microsoft has not published the information exposed, the request path involved, or the operation that mishandles untrusted input. Successful exploitation discloses sensitive information and corrupts identity trust decisions, with no reported ability to interrupt the service.

The record

CVE
CVE-2026-40379
Published
May 12, 2026
Updated
May 12, 2026
Vendor
Microsoft
Product
Microsoft Entra security token service
Classifications
CWE-200
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 12, 2026CVE publishedPublication date reported by the CVE source.
  2. May 12, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=-

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Microsoft · Microsoft Entra security token serviceversion=-

Published CVSS scores

9.3Microsoft CorporationCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N
7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-200Exposure of Sensitive Information to an Unauthorized Actor

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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