Critical [CVE-2026-55040] Microsoft SharePoint Server Security Feature Bypass Vulnerability
This critical-severity Microsoft Server advisory covers CVE-2026-55040 affecting Microsoft SharePoint Enterprise Server 2016, Microsoft SharePoint Server 2019, Microsoft SharePoint Server Subscription Edition.
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Summary
Microsoft SharePoint Server Security Feature Bypass Vulnerability
Affected products named by the advisory: Microsoft SharePoint Enterprise Server 2016; Microsoft SharePoint Server 2019; Microsoft SharePoint Server Subscription Edition.
CISA Known Exploited Vulnerability
- Listed:
- Aug 18, 2026 · federal remediation due Aug 21, 2026
- Required action:
- Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.
- Ransomware use:
- Unknown
KEV is a prioritization signal from CISA — remediation detail still comes from the vendor advisory.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · high-confidence parse· fetched 1 month ago·verify at source
- KB5002891 (build 16.0.5561.1001)
- KB5002883 (build 16.0.10417.20175)
- KB5002882 (build 16.0.19725.20434)
Official advisory · high-confidence parse· fetched 1 month ago·verify at source
Mitigation checklist
- Install the applicable security update for your platform: KB5002891, KB5002883, KB5002882 (see the Microsoft Update Catalog).
Official advisory · high-confidence parse· fetched 1 month ago·verify at source
Discussion(0)
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