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PatchSiren cyber security CVE debrief

CVE-2026-64921 Microsoft CVE debrief

Microsoft SharePoint Server Elevation of Privilege Vulnerability allows an authorized attacker to elevate privileges over a network due to missing authentication for a critical function. This vulnerability affects Microsoft Office SharePoint, potentially impacting deployments with versions prior to 16.0.5565.1001 (2016), 16.0.10417.20198 (2019), and 16.0.19725.20522 (Subscription Edition). Defenders should assess exposure and prioritize remediation based on the organization's specific configurations and versions in use.

Vendor
Microsoft
Product
Microsoft SharePoint Enterprise Server 2016
CVSS
HIGH 8.8
CISA KEV
Not listed in stored evidence
Original CVE published
2026-08-11
Original CVE updated
2026-10-08
Advisory published
2026-08-11
Advisory updated
2026-10-08

Who should care

Defenders responsible for Microsoft SharePoint Server deployments, particularly those with versions prior to 16.0.5565.1001 (2016), 16.0.10417.20198 (2019), and 16.0.19725.20522 (Subscription Edition), should assess exposure and prioritize remediation.

Why it matters

CVE-2026-64921 allows an authorized attacker to elevate privileges over a network due to missing authentication for a critical function in Microsoft SharePoint Server. Defenders should prioritize verifying and applying patches, assessing exposure, and implementing compensating controls.

  • Verify and apply patches for affected Microsoft SharePoint Server versions to prevent privilege elevation
  • Assess exposure and prioritize remediation for vulnerable deployments
  • Implement compensating controls to limit the attack surface

Technical summary

The vulnerability exists due to missing authentication for a critical function in Microsoft Office SharePoint, allowing an authorized attacker to elevate privileges over a network. This issue impacts Microsoft SharePoint Server deployments, particularly those with versions prior to 16.0.5565.1001 (2016), 16.0.10417.20198 (2019), and 16.0.19725.20522 (Subscription Edition). Defenders should prioritize verifying and applying patches, assessing exposure, and implementing compensating controls to limit the attack surface.

Defensive priority

Defenders should prioritize verifying and applying patches for affected Microsoft SharePoint Server versions, assessing exposure, and implementing compensating controls.

Recommended defensive actions

  • Verify and apply patches for affected Microsoft SharePoint Server versions
  • Assess exposure and prioritize remediation
  • Implement compensating controls and monitor for suspicious activity

Evidence notes

The CVE record and source item provide details on the vulnerability, affected versions, and vendor advisory. However, additional information on exploitation and impact is limited.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-64921 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-64921

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

  • CVE-2026-64921 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-64921

    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.