Occurred Aug 18, 2026, 12:00:00 AM UTC

First published Oct 27, 2026, 8:14:15 PM UTC · Last updated Oct 27, 2026, 8:14:15 PM UTC

CVE-2026-55040: Microsoft SharePoint Weak Authentication Vulnerability

Reported by CISA Known Exploited Vulnerabilities

A Microsoft SharePoint weak-authentication flaw can let an unauthorized attacker bypass a security feature over a network. The source recommends applying vendor mitigations, following CISA guidance, or discontinuing use if mitigations are unavailable.

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Why it matters

The source calls for stakeholders to assess internet exposure and apply the specified mitigation or patching guidance.

Generated scores

Scores are based on the cited reporting and use a 1–10 scale. Read the methodology.

Confidence: 6/10How certain the assessment is based on the clarity and evidence in the cited reporting.
Geographic reach: 2/10How widely the event reaches, from a local area (1) to worldwide impact (10).
Global importance: 3/10The event's broader significance, from limited importance (1) to major global importance (10).
Impact magnitude: 3/10The scale or severity of the real-world impact, from minor (1) to extreme (10).
Urgency: 5/10How time-sensitive the event is, from low urgency (1) to immediate attention needed (10).

Primary official sources

CISA Known Exploited Vulnerabilities CVE-2026-55040: Microsoft SharePoint Weak Authentication Vulnerability

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