Microsoft SharePoint Weak Authentication Vulnerability
Description
Microsoft SharePoint contains a weak authentication vulnerability which allows an unauthorized attacker to bypass a security feature over a network.
What to do
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.
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Details
- Vendor
- Microsoft
- Product
- SharePoint
- CVE
- CVE-2026-55040
- Affected versions
- Microsoft SharePoint Enterprise Server 2016 16.0: from 16.0.0 to 16.0.5561.1001 (excluded) — fixed in 16.0.5561.1001
Microsoft SharePoint Server 2019 16.0: from 16.0.0 to 16.0.10417.20175 (excluded) — fixed in 16.0.10417.20175
Microsoft SharePoint Server Subscription Edition 16.0: from 16.0.0 to 16.0.19725.20434 (excluded) — fixed in 16.0.19725.20434 (from the advisory and NVD; check the exact builds in the official advisory) - CVSS score
- 9.1
- Actively exploited
- Yes, listed in the CISA Known Exploited Vulnerabilities catalog
- CISA due date
- August 21, 2026 (deadline for US federal agencies: a good benchmark for you too)
- Source
- CISA KEV – original advisory
- Published
- August 18, 2026
The description and the recommended action are quoted from the public advisory; severity, exploitation status and affected versions are compiled automatically from public sources and may contain errors. The vendor's original advisory prevails: check it before taking action. This information is provided without warranty and does not replace a professional assessment.