CRITICAL Actively exploited CWE-1390
CVE-2026-55040
Microsoft SharePoint Server Security Feature Bypass Vulnerability
Microsoft·SharePoint
9.1/ 10
CVSS 3.1
Critical severity
70%
EPSS exploit odds
Chance of exploitation in the next 30 days
Higher than 99.4% of all CVEs
Listed
CISA KEV catalog
- Added
- Aug 18, 2026
- Fix due
- Aug 21, 2026
- Ransomware
- Not known
Timeline
- Published
- Jul 14, 2026
- Updated
- Nov 1, 2026
- First covered
- Jul 17, 2026
- Latest story
- 1 month ago
Summary
Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.
CWE-1390Weak Authentication
Attack profile
Attack vectorNetwork
ComplexityLow
PrivilegesNone
User interactionNone
ScopeUnchanged
ConfidentialityHigh
IntegrityHigh
AvailabilityNone
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N/E:U/RL:O/RC:CCISA 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.
Affected products
- Microsoft SharePoint Enterprise Server 201616.0.0 to before 16.0.5561.1001
- Microsoft SharePoint Server 201916.0.0 to before 16.0.10417.20175
- Microsoft SharePoint Server Subscription Edition16.0.0 to before 16.0.19725.20434