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CVE-2026-21527 Microsoft CVE debrief

CVE-2026-21527 is a medium-severity vulnerability in Microsoft Exchange Server that allows an unauthorized attacker to perform spoofing over a network. The vulnerability has a CVSS score of 6.5 and was first published on 2026-02-10.

Vendor
Microsoft
Product
Exchange Server
CVSS
MEDIUM 6.5
CISA KEV
Not listed in stored evidence
Original CVE published
2026-02-10
Original CVE updated
2026-06-15
Advisory published
2026-02-10
Advisory updated
2026-06-15

Who should care

Administrators and users of Microsoft Exchange Server 2016, 2019, and Subscription Edition should be aware of this vulnerability and take necessary actions to mitigate it.

Technical summary

The vulnerability is caused by a user interface (UI) misrepresentation of critical information in Microsoft Exchange Server. This allows an unauthorized attacker to perform spoofing over a network.

Defensive priority

MEDIUM

Recommended defensive actions

  • Apply patches or updates provided by Microsoft to fix the vulnerability.
  • Refer to [ref-4](https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21527) for mitigation or vendor reference.

Evidence notes

The vulnerability is analyzed and has a CWE classification of CWE-345, CWE-451, and CWE-1286.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-21527 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-21527

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-21527 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-21527

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental 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.