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High7.5Microsoft Server

High [CVE-2026-21511] Microsoft Outlook Spoofing Vulnerability

This high-severity Microsoft Server advisory covers CVE-2026-21511 affecting Microsoft SharePoint Enterprise Server 2016, Microsoft SharePoint Server 2019, Microsoft SharePoint Server Subscription Edition.

CVE-2026-21511 Published Feb 10, 2026Updated by vendor Aug 19, 2026
CVE-2026-21511
Affected products & platforms
Microsoft ServerSharePoint Server
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Summary

Deserialization of untrusted data in Microsoft Office Outlook allows an unauthorized attacker to perform spoofing over a network.

Affected products named by the advisory: Microsoft SharePoint Enterprise Server 2016; Microsoft SharePoint Server 2019; Microsoft SharePoint Server Subscription Edition.

Affected versions
  • Microsoft 365 Apps for Enterprise 16.0.1 before https://aka.ms/OfficeSecurityReleases
  • Microsoft Office 2019 19.0.0 before https://aka.ms/OfficeSecurityReleases
  • Microsoft Office LTSC 2021 16.0.1 before https://aka.ms/OfficeSecurityReleases
  • Microsoft Office LTSC 2024 16.0.0 before https://aka.ms/OfficeSecurityReleases
  • Microsoft Office LTSC for Mac 2021 16.0.1 before 16.106.26020821
  • Microsoft Office LTSC for Mac 2024 16.0.0 before 16.106.26020821
  • Microsoft SharePoint Enterprise Server 2016 16.0.0 before 16.0.5539.1002
  • Microsoft SharePoint Server 2019 16.0.0 before 16.0.10417.20097
  • Microsoft SharePoint Server Subscription Edition 16.0.0 before 16.0.19127.20518
  • Microsoft Word 2016 16.0.1 before 16.0.5539.1002

Official advisory · high-confidence parse· fetched 2 hours ago·verify at source

Fixed versions
  • https://aka.ms/OfficeSecurityReleases
  • 16.106.26020821
  • 16.0.5539.1002
  • 16.0.10417.20097
  • 16.0.19127.20518

Official advisory · high-confidence parse· fetched 2 hours ago·verify at source

Mitigation

Upgrade to a fixed release: https://aka.ms/OfficeSecurityReleases, 16.106.26020821, 16.0.5539.1002, 16.0.10417.20097, 16.0.19127.20518. That is the remediation for this advisory.

The vendor advisory may list additional interim mitigations or workarounds not captured here — review it before change work.

Official advisory · high-confidence parse· fetched 2 hours ago·verify at source

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